openSUSE Leap 42.2


Publication Date: November 15, 2016
About This Guide
Available Documentation
Documentation Conventions
About the Making of This Documentation
Source Code
I Advanced Administration
1 YaST in Text Mode
1.1 Navigation in Modules
1.2 Restriction of Key Combinations
1.3 YaST Command Line Options
2 Managing Software with Command Line Tools
2.1 Using Zypper
2.2 RPM—the Package Manager
3 System Recovery and Snapshot Management with Snapper
3.1 Default Setup
3.2 Using Snapper to Undo Changes
3.3 System Rollback by Booting from Snapshots
3.4 Creating and Modifying Snapper Configurations
3.5 Manually Creating and Managing Snapshots
3.6 Automatic Snapshot Clean-Up
3.7 Frequently Asked Questions
4 Remote Access with VNC
4.1 The vncviewer Client
4.2 One-time VNC Sessions
4.3 Persistent VNC Sessions
5 Advanced Disk Setup
5.1 Using the YaST Partitioner
5.2 LVM Configuration
5.3 Soft RAID Configuration with YaST
6 Installing Multiple Kernel Versions
6.1 Enabling and Configuring Multiversion Support
6.2 Installing/Removing Multiple Kernel Versions with YaST
6.3 Installing/Removing Multiple Kernel Versions with Zypper
7 GNOME Configuration for Administrators
7.1 Starting Applications Automatically
7.2 Automounting and Managing Media Devices
7.3 Changing Preferred Applications
7.4 Adding Document Templates
7.5 For More Information
II System
8 32-Bit and 64-Bit Applications in a 64-Bit System Environment
8.1 Runtime Support
8.2 Software Development
8.3 Software Compilation on Biarch Platforms
8.4 Kernel Specifications
9 Booting a Linux System
9.1 The Linux Boot Process
9.2 initramfs
9.3 Init on initramfs
10 The systemd Daemon
10.1 The systemd Concept
10.2 Basic Usage
10.3 System Start and Target Management
10.4 Managing Services with YaST
10.5 Customization of systemd
10.6 Advanced Usage
10.7 More Information
11 journalctl: Query the systemd Journal
11.1 Making the Journal Persistent
11.2 journalctl Useful Switches
11.3 Filtering the Journal Output
11.4 Investigating systemd Errors
11.5 Journald Configuration
11.6 Using YaST to Filter the systemd Journal
12 The Boot Loader GRUB 2
12.1 Main Differences between GRUB Legacy and GRUB 2
12.2 Configuration File Structure
12.3 Configuring the Boot Loader with YaST
12.4 Differences in Terminal Usage on z Systems
12.5 Helpful GRUB 2 Commands
12.6 More Information
13 Basic Networking
13.1 IP Addresses and Routing
13.2 IPv6—The Next Generation Internet
13.3 Name Resolution
13.4 Configuring a Network Connection with YaST
13.5 NetworkManager
13.6 Configuring a Network Connection Manually
13.7 Basic Router Setup
13.8 Setting Up Bonding Devices
13.9 Setting Up Team Devices for Network Teaming
13.10 Software-Defined Networking with Open vSwitch
14 UEFI (Unified Extensible Firmware Interface)
14.1 Secure Boot
14.2 For More Information
15 Special System Features
15.1 Information about Special Software Packages
15.2 Virtual Consoles
15.3 Keyboard Mapping
15.4 Language and Country-Specific Settings
16 Dynamic Kernel Device Management with udev
16.1 The /dev Directory
16.2 Kernel uevents and udev
16.3 Drivers, Kernel Modules and Devices
16.4 Booting and Initial Device Setup
16.5 Monitoring the Running udev Daemon
16.6 Influencing Kernel Device Event Handling with udev Rules
16.7 Persistent Device Naming
16.8 Files used by udev
16.9 For More Information
III Services
17 SLP
17.1 The SLP Front-End slptool
17.2 Providing Services via SLP
17.3 For More Information
18 Time Synchronization with NTP
18.1 Configuring an NTP Client with YaST
18.2 Manually Configuring NTP in the Network
18.3 Dynamic Time Synchronization at Runtime
18.4 Setting Up a Local Reference Clock
19 The Domain Name System
19.1 DNS Terminology
19.2 Installation
19.3 Configuration with YaST
19.4 Starting the BIND Name Server
19.5 The /etc/named.conf Configuration File
19.6 Zone Files
19.7 Dynamic Update of Zone Data
19.8 Secure Transactions
19.9 DNS Security
19.10 For More Information
20.1 Configuring a DHCP Server with YaST
20.2 DHCP Software Packages
20.3 The DHCP Server dhcpd
20.4 For More Information
21 Samba
21.1 Terminology
21.2 Installing a Samba Server
21.3 Starting and Stopping Samba
21.4 Configuring a Samba Server
21.5 Configuring Clients
21.6 Samba as Login Server
21.7 Samba Server in the Network with Active Directory
21.8 Advanced Topics
21.9 For More Information
22 Sharing File Systems with NFS
22.1 Terminology
22.2 Installing NFS Server
22.3 Configuring NFS Server
22.4 Configuring Clients
22.5 For More Information
23 On-Demand Mounting with Autofs
23.1 Installation
23.2 Configuration
23.3 Operation and Debugging
23.4 Auto-Mounting an NFS Share
23.5 Advanced Topics
24 The Apache HTTP Server
24.1 Quick Start
24.2 Configuring Apache
24.3 Starting and Stopping Apache
24.4 Installing, Activating, and Configuring Modules
24.5 Enabling CGI Scripts
24.6 Setting Up a Secure Web Server with SSL
24.7 Running Multiple Apache Instances on the Same Server
24.8 Avoiding Security Problems
24.9 Troubleshooting
24.10 For More Information
25 Setting Up an FTP Server with YaST
25.1 Starting the FTP Server
25.2 FTP General Settings
25.3 FTP Performance Settings
25.4 Authentication
25.5 Expert Settings
25.6 For More Information
26 The Proxy Server Squid
26.1 Some Facts about Proxy Caches
26.2 System Requirements
26.3 Basic Usage of Squid
26.4 The /etc/squid/squid.conf Configuration File
26.5 Configuring a Transparent Proxy
26.6 Using the Squid Cache Manager CGI Interface (cachemgr.cgi)
26.7 squidGuard
26.8 Cache Report Generation with Calamaris
26.9 For More Information
IV Mobile Computers
27 Mobile Computing with Linux
27.1 Laptops
27.2 Mobile Hardware
27.3 Cellular Phones and PDAs
27.4 For More Information
28 Using NetworkManager
28.1 Use Cases for NetworkManager
28.2 Enabling or Disabling NetworkManager
28.3 Configuring Network Connections
28.4 NetworkManager and Security
28.5 Frequently Asked Questions
28.6 Troubleshooting
28.7 For More Information
29 Power Management
29.1 Power Saving Functions
29.2 Advanced Configuration and Power Interface (ACPI)
29.3 Rest for the Hard Disk
29.4 Troubleshooting
29.5 For More Information
A An Example Network
B GNU Licenses
B.1 GNU Free Documentation License
List of Figures
1.1 Main Window of YaST in Text Mode
1.2 The Software Installation Module
3.1 Boot Loader: Snapshots
4.1 vncviewer
5.1 The YaST Partitioner
5.2 Btrfs Subvolumes in YaST Partitioner
5.3 Creating a Volume Group
5.4 Logical Volume Management
5.5 RAID Partitions
6.1 The YaST Software Manager: Multiversion View
10.1 Services Manager
11.1 YaST systemd Journal
12.1 GRUB 2 Boot Editor
12.2 Boot Code Options
12.3 Boot loader Options
12.4 Kernel Parameters
12.5 Code Options
13.1 Simplified Layer Model for TCP/IP
13.2 TCP/IP Ethernet Packet
13.3 Configuring Network Settings
13.4 wicked architecture
14.1 Secure Boot Support
14.2 UEFI: Secure Boot Process
18.1 YaST: NTP Server
18.2 Advanced NTP Configuration: Security Settings
19.1 DNS Server Installation: Forwarder Settings
19.2 DNS Server Installation: DNS Zones
19.3 DNS Server Installation: Finish Wizard
19.4 DNS Server: Logging
19.5 DNS Server: Zone Editor (Basics)
19.6 DNS Server: Zone Editor (NS Records)
19.7 DNS Server: Zone Editor (MX Records)
19.8 DNS Server: Zone Editor (SOA)
19.9 Adding a Record for a Master Zone
19.10 Adding a Reverse Zone
19.11 Adding a Reverse Record
20.1 DHCP Server: Card Selection
20.2 DHCP Server: Global Settings
20.3 DHCP Server: Dynamic DHCP
20.4 DHCP Server: Start-Up
20.5 DHCP Server: Host Management
20.6 DHCP Server: Chroot Jail and Declarations
20.7 DHCP Server: Selecting a Declaration Type
20.8 DHCP Server: Configuring Subnets
20.9 DHCP Server: TSIG Configuration
20.10 DHCP Server: Interface Configuration for Dynamic DNS
20.11 DHCP Server: Network Interface and Firewall
21.1 Determining Windows Domain Membership
21.2 Windows Explorer Advanced Attributes Dialog
21.3 Windows Explorer Directory Listing with Compressed Files
21.4 Adding a New Samba Share with Snapshotting Enabled
21.5 The Previous Versions tab in Windows Explorer
22.1 NFS Server Configuration Tool
24.1 HTTP Server Wizard: Default Host
24.2 HTTP Server Wizard: Summary
24.3 HTTP Server Configuration: Listen Ports and Addresses
24.4 HTTP Server Configuration: Server Modules
25.1 FTP Server Configuration — Start-Up
27.1 Integrating a Mobile Computer in an Existing Environment
28.1 GNOME Network Connections Dialog
List of Examples
2.1 Zypper—List of Known Repositories
2.2 rpm -q -i wget
2.3 Script to Search for Packages
3.1 Keep the Last 10 Important and Regular Snapshots Regardless of Age
3.2 Only Keep Snapshots Younger Than Ten Days
3.3 Example timeline configuration
10.1 List Active Services
10.2 List Failed Services
10.3 List all Processes Belonging to a Service
12.1 Usage of grub2-mkconfig
12.2 Usage of grub2-mkrescue
12.3 Usage of grub2-script-check
12.4 Usage of grub2-once
13.1 Writing IP Addresses
13.2 Linking IP Addresses to the Netmask
13.3 Sample IPv6 Address
13.4 IPv6 Address Specifying the Prefix Length
13.5 Common Network Interfaces and Some Static Routes
13.6 /etc/resolv.conf
13.7 /etc/hosts
13.8 /etc/networks
13.9 /etc/host.conf
13.10 /etc/nsswitch.conf
13.11 Output of the Command ping
13.12 Configuration for Loadbalancing with Network Teaming
13.13 Configuration for DHCP Network Teaming Device
15.1 Entry in /etc/crontab
15.2 /etc/crontab: Remove Time Stamp Files
15.3 Example for /etc/logrotate.conf
15.4 ulimit: Settings in ~/.bashrc
16.1 Example udev Rules
19.1 Forwarding Options in named.conf
19.2 A Basic /etc/named.conf
19.3 Entry to Disable Logging
19.4 Zone Entry for
19.5 Zone Entry for
19.6 The /var/lib/named/ File
19.7 Reverse Lookup
20.1 The Configuration File /etc/dhcpd.conf
20.2 Additions to the Configuration File
21.1 A CD-ROM Share
21.2 [homes] Share
21.3 Global Section in smb.conf
21.4 Using rpcclient to Request a Windows Server 2012 Share Snapshot
24.1 Basic Examples of Name-Based VirtualHost Entries
24.2 Name-Based VirtualHost Directives
24.3 IP-Based VirtualHost Directives
24.4 Basic VirtualHost Configuration
24.5 VirtualHost CGI Configuration
26.1 A Request With squidclient
26.2 Defining ACL Rules

Copyright © 2006– 2016 SUSE LLC and contributors. All rights reserved.

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or (at your option) version 1.3; with the Invariant Section being this copyright notice and license. A copy of the license version 1.2 is included in the section entitled GNU Free Documentation License.

For SUSE trademarks, see All other third-party trademarks are the property of their respective owners. Trademark symbols (®, ™ etc.) denote trademarks of SUSE and its affiliates. Asterisks (*) denote third-party trademarks.

All information found in this book has been compiled with utmost attention to detail. However, this does not guarantee complete accuracy. Neither SUSE LLC, its affiliates, the authors nor the translators shall be held liable for possible errors or the consequences thereof.

About This Guide

This manual gives you a general understanding of openSUSE® Leap. It is intended mainly for system administrators and home users with basic system administration knowledge. Check out the various parts of this manual for a selection of applications needed in everyday life and in-depth descriptions of advanced installation and configuration scenarios.

Advanced Administration

Learn about advanced adminstrations tasks such as using YaST in text mode and managing software from the command line. Find out how to do system roll-backs with Snapper and how to use advanced storage techniques on openSUSE Leap.


Get an introduction to the components of your Linux system and a deeper understanding of their interaction.


Learn how to configure the various network and file services that come with openSUSE Leap.

Mobile Computers

Get an introduction to mobile computing with openSUSE Leap, get to know the various options for wireless computing and power management.

Many chapters in this manual contain links to additional documentation resources. These include additional documentation that is available on the system and documentation available on the Internet.

For an overview of the documentation available for your product and the latest documentation updates, refer to or to the following section.

1 Available Documentation

We provide HTML and PDF versions of our books in different languages. The following manuals for users and administrators are available for this product:

Book “Start-Up

This manual will see you through your initial contact with openSUSE® Leap. Check out the various parts of this manual to learn how to install, use and enjoy your system.


Covers system administration tasks like maintaining, monitoring and customizing an initially installed system.

Book “Virtualization Guide

Describes virtualization technology in general, and introduces libvirt—the unified interface to virtualization—and detailed information on specific hypervisors.

Book “AutoYaST”

AutoYaST is a system for installing one or more openSUSE Leap systems automatically and without user intervention, using an AutoYaST profile that contains installation and configuration data. The manual guides you through the basic steps of auto-installation: preparation, installation, and configuration.

Book “Security Guide

Introduces basic concepts of system security, covering both local and network security aspects. Shows how to use the product inherent security software like AppArmor or the auditing system that reliably collects information about any security-relevant events.

Book “System Analysis and Tuning Guide

An administrator's guide for problem detection, resolution and optimization. Find how to inspect and optimize your system by means of monitoring tools and how to efficiently manage resources. Also contains an overview of common problems and solutions and of additional help and documentation resources.

Book “GNOME User Guide

Introduces the GNOME desktop of openSUSE Leap. It guides you through using and configuring the desktop and helps you perform key tasks. It is intended mainly for end users who want to make efficient use of GNOME as their default desktop.

Find HTML versions of most product manuals in your installed system under /usr/share/doc/manual. The latest documentation updates are available at where you can download the documentation for your product in various formats.

2 Feedback

Several feedback channels are available:

Bugs and Enhancement Requests

For services and support options available for your product, refer to

To report bugs for a product component, go to, log in, and click Create New.

User Comments

We want to hear your comments about and suggestions for this manual and the other documentation included with this product. Use the User Comments feature at the bottom of each page in the online documentation or go to and enter your comments there.


For feedback on the documentation of this product, you can also send a mail to Make sure to include the document title, the product version and the publication date of the documentation. To report errors or suggest enhancements, provide a concise description of the problem and refer to the respective section number and page (or URL).

3 Documentation Conventions

The following notices and typographical conventions are used in this documentation:

  • /etc/passwd: directory names and file names

  • PLACEHOLDER: replace PLACEHOLDER with the actual value

  • PATH: the environment variable PATH

  • ls, --help: commands, options, and parameters

  • user: users or groups

  • package name : name of a package

  • Alt, AltF1: a key to press or a key combination; keys are shown in uppercase as on a keyboard

  • File, File › Save As: menu items, buttons

  • Dancing Penguins (Chapter Penguins, ↑Another Manual): This is a reference to a chapter in another manual.

  • Commands that must be run with root privileges. Often you can also prefix these commands with the sudo command to run them.

    root # command
  • Commands that can be run by non-privileged users.

    tux > command
  • Notices

    Warning: Warning Notice

    Vital information you must be aware of before proceeding. Warns you about security issues, potential loss of data, damage to hardware, or physical hazards.

    Important: Important Notice

    Important information you should be aware of before proceeding.

    Note: Note Notice

    Additional information, for example about differences in software versions.

    Tip: Tip Notice

    Helpful information, like a guideline or a piece of practical advice.

4 About the Making of This Documentation

This documentation is written in SUSEDoc, a subset of DocBook 5. The XML source files were validated by jing (see, processed by xsltproc, and converted into XSL-FO using a customized version of Norman Walsh's stylesheets. The final PDF is formatted through FOP from Apache Software Foundation. The open source tools and the environment used to build this documentation are provided by the DocBook Authoring and Publishing Suite (DAPS). The project's home page can be found at

The XML source code of this documentation can be found at

5 Source Code

The source code of openSUSE Leap is publicly available. Refer to for download links and more information.

6 Acknowledgments

With a lot of voluntary commitment, the developers of Linux cooperate on a global scale to promote the development of Linux. We thank them for their efforts—this distribution would not exist without them. Special thanks, of course, goes to Linus Torvalds.

Part I Advanced Administration

1 YaST in Text Mode

This section is intended for system administrators and experts who do not run an X server on their systems and depend on the text-based installation tool. It provides basic information about starting and operating YaST in text mode.

2 Managing Software with Command Line Tools

This chapter describes Zypper and RPM, two command line tools for managing software. For a definition of the terminology used in this context (for example, repository, patch, or update) refer to Book “Start-Up”, Chapter 9 “Installing or Removing Software”, Section 9.1 “Definition of Terms”.

3 System Recovery and Snapshot Management with Snapper

Being able to do file system snapshots providing the ability to do rollbacks on Linux is a feature that was often requested in the past. Snapper, with the Btrfs file system or thin-provisioned LVM volumes now fills that gap.

Btrfs, a new copy-on-write file system for Linux, supports file system snapshots (a copy of the state of a subvolume at a certain point of time) of subvolumes (one or more separately mountable file systems within each physical partition). Snapshots are also supported on thin-provisioned LVM volumes formatted with XFS, Ext4 or Ext3. Snapper lets you create and manage these snapshots. It comes with a command line and a YaST interface. Starting with SUSE Linux Enterprise Server 12 it is also possible to boot from Btrfs snapshots—see Section 3.3, “System Rollback by Booting from Snapshots” for more information.

4 Remote Access with VNC

Virtual Network Computing (VNC) enables you to control a remote computer via a graphical desktop (as opposed to a remote shell access). VNC is platform-independent and lets you access the remote machine from any operating system.

openSUSE Leap supports two different kinds of VNC sessions: One-time sessions that live as long as the VNC connection from the client is kept up, and persistent sessions that live until they are explicitly terminated.

5 Advanced Disk Setup

Sophisticated system configurations require specific disk setups. All common partitioning tasks can be done with YaST. To get persistent device naming with block devices, use the block devices below /dev/disk/by-id or /dev/disk/by-uuid. Logical Volume Management (LVM) is a disk partitioning scheme t…

6 Installing Multiple Kernel Versions

openSUSE Leap supports the parallel installation of multiple kernel versions. When installing a second kernel, a boot entry and an initrd are automatically created, so no further manual configuration is needed. When rebooting the machine, the newly added kernel is available as an additional boot option.

Using this functionality, you can safely test kernel updates while being able to always fall back to the proven former kernel. To do so, do not use the update tools (such as the YaST Online Update or the updater applet), but instead follow the process described in this chapter.

7 GNOME Configuration for Administrators

This chapter introduces GNOME configuration options which administrators can use to adjust system-wide settings, such as customizing menus, installing themes, configuring fonts, changing preferred applications, and locking down capabilities.

1 YaST in Text Mode

This section is intended for system administrators and experts who do not run an X server on their systems and depend on the text-based installation tool. It provides basic information about starting and operating YaST in text mode.

YaST in text mode uses the ncurses library to provide an easy pseudo-graphical user interface. The ncurses library is installed by default. The minimum supported size of the terminal emulator in which to run YaST is 80x25 characters.

Main Window of YaST in Text Mode
Figure 1.1: Main Window of YaST in Text Mode

When you start YaST in text mode, the YaST control center appears (see Figure 1.1). The main window consists of three areas. The left frame features the categories to which the various modules belong. This frame is active when YaST is started and therefore it is marked by a bold white border. The active category is selected. The right frame provides an overview of the modules available in the active category. The bottom frame contains the buttons for Help and Quit.

When you start the YaST control center, the category Software is selected automatically. Use and to change the category. To select a module from the category, activate the right frame with and then use and to select the module. Keep the arrow keys pressed to scroll through the list of available modules. The selected module is highlighted. Press Enter to start the active module.

Various buttons or selection fields in the module contain a highlighted letter (yellow by default). Use Althighlighted_letter to select a button directly instead of navigating there with →|. Exit the YaST control center by pressing AltQ or by selecting Quit and pressing Enter.

Tip: Refreshing YaST Dialogs

If a YaST dialog gets corrupted or distorted (for example, while resizing the window), press CtrlL to refresh and restore its contents.

1.1 Navigation in Modules

The following description of the control elements in the YaST modules assumes that all function keys and Alt key combinations work and are not assigned to different global functions. Read Section 1.2, “Restriction of Key Combinations” for information about possible exceptions.

Navigation among Buttons and Selection Lists

Use →| to navigate among the buttons and frames containing selection lists. To navigate in reverse order, use Alt→| or Shift→| combinations.

Navigation in Selection Lists

Use the arrow keys ( and ) to navigate among the individual elements in an active frame containing a selection list. If individual entries within a frame exceed its width, use Shift or Shift to scroll horizontally to the right and left. Alternatively, use CtrlE or CtrlA. This combination can also be used if using or results in changing the active frame or the current selection list, as in the control center.

Buttons, Radio Buttons, and Check Boxes

To select buttons with empty square brackets (check boxes) or empty parentheses (radio buttons), press Space or Enter. Alternatively, radio buttons and check boxes can be selected directly with Althighlighted_letter. In this case, you do not need to confirm with Enter. If you navigate to an item with →|, press Enter to execute the selected action or activate the respective menu item.

Function Keys

The F keys (F1 through F12) enable quick access to the various buttons. Available function key combinations (Fx) are shown in the bottom line of the YaST screen. Which function keys are actually mapped to which buttons depend on the active YaST module, because the different modules offer different buttons (Details, Info, Add, Delete, etc.). Use F10 for Accept, OK, Next, and Finish. Press F1 to access the YaST help.

Using Navigation Tree in ncurses Mode

Some YaST modules use a navigation tree in the left part of the window to select configuration dialogs. Use the arrow keys ( and ) to navigate in the tree. Use Space to open or close tree items. In ncurses mode, Enter must be pressed after a selection in the navigation tree to show the selected dialog. This is an intentional behavior to save time consuming redraws when browsing through the navigation tree.

Selecting Software in the Software Installation Module

Use the filters on the left side to limit the amount of displayed packages. Installed packages are marked with the letter i. To change the status of a package, press Space or Enter. Alternatively, use the Actions menu to select the needed status change (install, delete, update, taboo or lock).

The Software Installation Module
Figure 1.2: The Software Installation Module

1.2 Restriction of Key Combinations

If your window manager uses global Alt combinations, the Alt combinations in YaST might not work. Keys like Alt or Shift can also be occupied by the settings of the terminal.

Replacing Alt with Esc

Alt shortcuts can be executed with Esc instead of Alt. For example, EscH replaces AltH. (First press Esc, then press H.)

Backward and Forward Navigation with CtrlF and CtrlB

If the Alt and Shift combinations are occupied by the window manager or the terminal, use the combinations CtrlF (forward) and CtrlB (backward) instead.

Restriction of Function Keys

The F keys are also used for functions. Certain function keys might be occupied by the terminal and may not be available for YaST. However, the Alt key combinations and function keys should always be fully available on a pure text console.

1.3 YaST Command Line Options

Besides the text mode interface, YaST provides a pure command line interface. To get a list of YaST command line options, enter:

yast -h

1.3.1 Starting the Individual Modules

To save time, the individual YaST modules can be started directly. To start a module, enter:

yast <module_name>

View a list of all module names available on your system with yast -l or yast --list. Start the network module, for example, with yast lan.

1.3.2 Installing Packages from the Command Line

If you know a package name and the package is provided by any of your active installation repositories, you can use the command line option -i to install the package:

yast -i <package_name>


yast --install <package_name>

package_name can be a single short package name, for example gvim, which is installed with dependency checking, or the full path to an RPM package, which is installed without dependency checking.

If you need a command line based software management utility with functionality beyond what YaST provides, consider using Zypper. This utility uses the same software management library that is also the foundation for the YaST package manager. The basic usage of Zypper is covered in Section 2.1, “Using Zypper”.

1.3.3 Command Line Parameters of the YaST Modules

To use YaST functionality in scripts, YaST provides command line support for individual modules. Not all modules have command line support. To display the available options of a module, enter:

yast <module_name> help

If a module does not provide command line support, the module is started in text mode and the following message appears:

This YaST module does not support the command line interface.

2 Managing Software with Command Line Tools


This chapter describes Zypper and RPM, two command line tools for managing software. For a definition of the terminology used in this context (for example, repository, patch, or update) refer to Book “Start-Up”, Chapter 9 “Installing or Removing Software”, Section 9.1 “Definition of Terms”.

2.1 Using Zypper

Zypper is a command line package manager for installing, updating and removing packages a well as for managing repositories. It is especially useful for accomplishing remote software management tasks or managing software from shell scripts.

2.1.1 General Usage

The general syntax of Zypper is:

zypper [--global-options] COMMAND  [--command-options] [arguments]

The components enclosed in brackets are not required. See zypper help for a list of general options and all commands. To get help for a specific command, type zypper help COMMAND.

Zypper Commands

The simplest way to execute Zypper is to type its name, followed by a command. For example, to apply all needed patches to the system, use:

sudo zypper patch
Global Options

Additionally, you can choose from one or more global options by typing them immediately before the command:

sudo zypper --non-interactive patch

In the above example, the option --non-interactive means that the command is run without asking anything (automatically applying the default answers).

Command-Specific Options

To use options that are specific to a particular command, type them immediately after the command:

sudo zypper patch --auto-agree-with-licenses

In the above example, --auto-agree-with-licenses is used to apply all needed patches to a system without you being asked to confirm any licenses. Instead, license will be accepted automatically.


Some commands require one or more arguments. For example, when using the command install, you need to specify which package or which packages you want to install:

sudo zypper install mplayer

Some options also require a single argument. The following command will list all known patterns:

zypper search -t pattern

You can combine all of the above. For example, the following command will install the aspell-de and aspell-fr packages from the factory repository while being verbose:

sudo zypper -v install --from factory aspell-de aspell-fr

The --from option makes sure to keep all repositories enabled (for solving any dependencies) while requesting the package from the specified repository.

Most Zypper commands have a dry-run option that does a simulation of the given command. It can be used for test purposes.

sudo zypper remove --dry-run MozillaFirefox

Zypper supports the global --userdata STRING option. You can specify a string with this option, which gets written to Zypper's log files and plug-ins (such as the Btrfs plug-in). It can be used to mark and identify transactions in log files.

sudo zypper --userdata STRING patch

2.1.2 Installing and Removing Software with Zypper

To install or remove packages, use the following commands:

sudo zypper install PACKAGE_NAME
sudo zypper remove PACKAGE_NAME
Warning: Do Not Remove Mandatory System Packages

Do not remove mandatory system packages like glibc , zypper , kernel . If they are removed, the system can become unstable or stop working altogether. Selecting Which Packages to Install or Remove

There are various ways to address packages with the commands zypper install and zypper remove.

By Exact Package Name
sudo zypper install MozillaFirefox
By Exact Package Name and Version Number
sudo zypper install MozillaFirefox-3.5.3
By Repository Alias and Package Name
sudo zypper install mozilla:MozillaFirefox

Where mozilla is the alias of the repository from which to install.

By Package Name Using Wild Cards

You can select all packages that have names starting or ending with a certain string. Use wild cards with care, especially when removing packages. The following command will install all packages starting with Moz:

sudo zypper install 'Moz*'
Tip: Removing all -debuginfo Packages

When debugging a problem, you sometimes need to temporarily install a lot of -debuginfo packages which give you more information about running processes. After your debugging session finishes and you need to clean the environment, run the following:

sudo zypper remove '*-debuginfo'
By Capability

For example, if you want to install a Perl module without knowing the name of the package, capabilities come in handy:

sudo zypper install firefox
By Capability, Hardware Architecture, or Version

Together with a capability, you can specify a hardware architecture and a version:

  • The name of the desired hardware architecture is appended to the capability after a full stop. For example, to specify the AMD64/Intel 64 architectures (which in Zypper is named x86_64), use:

    sudo zypper install 'firefox.x86_64'
  • Versions must be appended to the end of the string and must be preceded by an operator: < (lesser than), <= (lesser than or equal), = (equal), >= (greater than or equal), > (greater than).

    sudo zypper install 'firefox>=3.5.3'
  • You can also combine a hardware architecture and version requirement:

    sudo zypper install 'firefox.x86_64>=3.5.3'
By Path to the RPM file

You can also specify a local or remote path to a package:

sudo zypper install /tmp/install/MozillaFirefox.rpm
sudo zypper install Combining Installation and Removal of Packages

To install and remove packages simultaneously, use the +/- modifiers. To install emacs and simultaneously remove vim , use:

sudo zypper install emacs -vim

To remove emacs and simultaneously install vim , use:

sudo zypper remove emacs +vim

To prevent the package name starting with the - being interpreted as a command option, always use it as the second argument. If this is not possible, precede it with --:

sudo zypper install -emacs +vim       # Wrong
sudo zypper install vim -emacs        # Correct
sudo zypper install -- -emacs +vim    # same as above
sudo zypper remove emacs +vim         # same as above Cleaning Up Dependencies of Removed Packages

If (together with a certain package), you automatically want to remove any packages that become unneeded after removing the specified package, use the --clean-deps option:

sudo zypper rm PACKAGE_NAME --clean-deps Using Zypper in Scripts

By default, Zypper asks for a confirmation before installing or removing a selected package, or when a problem occurs. You can override this behavior using the --non-interactive option. This option must be given before the actual command (install, remove, and patch), as can be seen in the following:

sudo zypper --non-interactive install PACKAGE_NAME

This option allows the use of Zypper in scripts and cron jobs. Installing or Downloading Source Packages

If you want to install the corresponding source package of a package, use:

zypper source-install PACKAGE_NAME

When executed as root, the default location to install source packages is /usr/src/packages/ and ~/rpmbuild when run as user. These values can be changed in your local rpm configuration.

This command will also install the build dependencies of the specified package. If you do not want this, add the switch -D. To install only the build dependencies use -d.

sudo zypper source-install -D PACKAGE_NAME # source package only
sudo zypper source-install -d PACKAGE_NAME # build dependencies only

Of course, this will only work if you have the repository with the source packages enabled in your repository list (it is added by default, but not enabled). See Section 2.1.5, “Managing Repositories with Zypper” for details on repository management.

A list of all source packages available in your repositories can be obtained with:

zypper search -t srcpackage

You can also download source packages for all installed packages to a local directory. To download source packages, use:

zypper source-download

The default download directory is /var/cache/zypper/source-download. You can change it using the --directory option. To only show missing or extraneous packages without downloading or deleting anything, use the --status option. To delete extraneous source packages, use the --delete option. To disable deleting, use the --no-delete option. Installing Packages from Disabled Repositories

Normally you can only install packages from enabled repositories. The --plus-content TAG option helps you specify repositories to be refreshed, temporarily enabled during the current Zypper session, and disabled after it completes.

For example, to enable repositories that may provide additional -debuginfo or -debugsource packages, use --plus-content debug. You can specify this option multiple times.

To temporarily enable such 'debug' repositories to install a specific -debuginfo package, use the option as follows:

sudo zypper --plus-content debug install "debuginfo(build-id)=eb844a5c20c70a59fc693cd1061f851fb7d046f4"

The build-id string is reported by gdb for missing debuginfo packages. Utilities

To verify whether all dependencies are still fulfilled and to repair missing dependencies, use:

zypper verify

In addition to dependencies that must be fulfilled, some packages recommend other packages. These recommended packages are only installed if actually available and installable. In case recommended packages were made available after the recommending package has been installed (by adding additional packages or hardware), use the following command:

sudo zypper install-new-recommends

This command is very useful after plugging in a Web cam or Wi-Fi device. It will install drivers for the device and related software, if available. Drivers and related software are only installable if certain hardware dependencies are fulfilled.

2.1.3 Updating Software with Zypper

There are three different ways to update software using Zypper: by installing patches, by installing a new version of a package or by updating the entire distribution. The latter is achieved with zypper dist-upgrade. Upgrading openSUSE Leap is discussed in Book “Start-Up”, Chapter 12 “Upgrading the System and System Changes”. Installing All Needed Patches

To install all officially released patches that apply to your system, run:

sudo zypper patch

All patches available from repositories configured on your computer are checked for their relevance to your installation. If they are relevant (and not classified as optional or feature), they are installed immediately.

If a patch that is about to be installed includes changes that require a system reboot, you will be warned before.

To install also optional patches, use:

sudo zypper patch --with-optional

To install all patches relating to a specific Bugzilla issue, use:

sudo zypper patch --bugzilla=NUMBER

To install all patches relating to a specific CVE database entry, use:

sudo zypper patch --cve=NUMBER

For example, to install a security patch with the CVE number CVE-2010-2713, execute:

sudo zypper patch --cve=CVE-2010-2713

To install only patches which affect Zypper and the package management itself, use:

sudo zypper patch --updatestack-only Listing Patches

To find out whether patches are available, Zypper allows viewing the following information:

Number of Needed Patches

To list the number of needed patches (patches that apply to your system but are not yet installed), use patch-check:

zypper patch-check
Loading repository data...
Reading installed packages...
5 patches needed (1 security patch)

This command can be combined with the --updatestack-only option to list only the patches which affect Zypper and the package management itself.

List of Needed Patches

To list all needed patches (patches that apply to your system but are not yet installed), use list-patches:

tux > zypper list-patches
Loading repository data...
Reading installed packages...

Repository     | Name        | Version | Category | Status  | Summary
SLES12-Updates | SUSE-2014-8 | 1       | security | needed  | openssl: Update for OpenSSL
List of All Patches

To list all patches available for openSUSE Leap, regardless of whether they are already installed or apply to your installation, use zypper patches.

It is also possible to list and install patches relevant to specific issues. To list specific patches, use the zypper list-patches command with the following options:

By Bugzilla Issues

To list all needed patches that relate to Bugzilla issues, use the option --bugzilla.

To list patches for a specific bug, you can also specify a bug number: --bugzilla=NUMBER. To search for patches relating to multiple Bugzilla issues, add commas between the bug numbers, for example:

zypper list-patches --bugzilla=972197,956917
By CVE Number

To list all needed patches that relate to an entry in the CVE database (Common Vulnerabilities and Exposures), use the option --cve.

To list patches for a specific CVE database entry, you can also specify a CVE number: --cve=NUMBER. To search for patches relating to multiple CVE database entries, add commas between the CVE numbers, for example:

zypper list-patches --bugzilla=CVE-2016-2315,CVE-2016-2324

To list all patches regardless of whether they are needed, use the option --all additionally. For example, to list all patches with a CVE number assigned, use:

tux > zypper list-patches --all --cve
Issue | No.           | Patch             | Category    | Severity  | Status
cve   | CVE-2015-0287 | SUSE-SLE-Module.. | recommended | moderate  | needed
cve   | CVE-2014-3566 | SUSE-SLE-SERVER.. | recommended | moderate  | not needed
[...] Installing New Package Versions

If a repository contains only new packages, but does not provide patches, zypper patch does not show any effect. To update all installed packages with newer available versions (while maintaining system integrity), use:

sudo zypper update

To update individual packages, specify the package with either the update or install command:

sudo zypper update PACKAGE_NAME
sudo zypper install PACKAGE_NAME

A list of all new installable packages can be obtained with the command:

zypper list-updates

Note that this command only lists packages that match the following criteria:

  • has the same vendor like the already installed package,

  • is provided by repositories with at least the same priority than the already installed package,

  • is installable (all dependencies are satisfied).

A list of all new available packages (regardless whether installable or not) can be obtained with:

sudo zypper list-updates --all

To find out why a new package cannot be installed, use the zypper install or zypper update command as described above. Identifying Orphaned Packages

Whenever you remove a repository from Zypper or upgrade your system, some packages can get in an orphaned state. These orphaned packages belong to no active repository anymore. The following command gives you a list of these:

sudo zypper packages --orphaned

With this list, you can decide if a package is still needed or can be removed safely.

2.1.4 Identifying Processes and Services Using Deleted Files

When patching, updating or removing packages, there may be running processes on the system which continue to use files having been deleted by the update or removal. Use zypper ps to list processes using deleted files. In case the process belongs to a known service, the service name is listed, making it easy to restart the service. By default zypper ps shows a table:

tux > zypper ps
PID   | PPID | UID | User  | Command      | Service      | Files
814   | 1    | 481 | avahi | avahi-daemon | avahi-daemon | /lib64/ld-2.19.s->
      |      |     |       |              |              | /lib64/libdl-2.1->
      |      |     |       |              |              | /lib64/libpthrea->
      |      |     |       |              |              | /lib64/libc-2.19->
PID: ID of the process
PPID: ID of the parent process
UID: ID of the user running the process
Login: Login name of the user running the process
Command: Command used to execute the process
Service: Service name (only if command is associated with a system service)
Files: The list of the deleted files

The output format of zypper ps can be controlled as follows:

zypper ps-s

Create a short table not showing the deleted files.

tux > zypper ps -s
PID   | PPID | UID  | User    | Command      | Service
814   | 1    | 481  | avahi   | avahi-daemon | avahi-daemon
817   | 1    | 0    | root    | irqbalance   | irqbalance
1567  | 1    | 0    | root    | sshd         | sshd
1761  | 1    | 0    | root    | master       | postfix
1764  | 1761 | 51   | postfix | pickup       | postfix
1765  | 1761 | 51   | postfix | qmgr         | postfix
2031  | 2027 | 1000 | tux     | bash         |
zypper ps-ss

Show only processes associated with a system service.

PID   | PPID | UID  | User    | Command      | Service
814   | 1    | 481  | avahi   | avahi-daemon | avahi-daemon
817   | 1    | 0    | root    | irqbalance   | irqbalance
1567  | 1    | 0    | root    | sshd         | sshd
1761  | 1    | 0    | root    | master       | postfix
1764  | 1761 | 51   | postfix | pickup       | postfix
1765  | 1761 | 51   | postfix | qmgr         | postfix
zypper ps-sss

Only show system services using deleted files.

zypper ps--print "systemctl status %s"

Show the commands to retrieve status information for services which might need a restart.

systemctl status avahi-daemon
systemctl status irqbalance
systemctl status postfix
systemctl status sshd

For more information about service handling refer to Chapter 10, The systemd Daemon.

2.1.5 Managing Repositories with Zypper

All installation or patch commands of Zypper rely on a list of known repositories. To list all repositories known to the system, use the command:

zypper repos

The result will look similar to the following output:

Example 2.1: Zypper—List of Known Repositories
tux > zypper repos
# | Alias        | Name          | Enabled | Refresh
1 | SLEHA-12-GEO | SLEHA-12-GEO  | Yes     | No
2 | SLEHA-12     | SLEHA-12      | Yes     | No
3 | SLES12       | SLES12        | Yes     | No

When specifying repositories in various commands, an alias, URI or repository number from the zypper repos command output can be used. A repository alias is a short version of the repository name for use in repository handling commands. Note that the repository numbers can change after modifying the list of repositories. The alias will never change by itself.

By default, details such as the URI or the priority of the repository are not displayed. Use the following command to list all details:

zypper repos -d Adding Repositories

To add a repository, run

sudo zypper addrepo URI ALIAS

URI can either be an Internet repository, a network resource, a directory or a CD or DVD (see for details). The ALIAS is a shorthand and unique identifier of the repository. You can freely choose it, with the only exception that it needs to be unique. Zypper will issue a warning if you specify an alias that is already in use. Removing Repositories

If you want to remove a repository from the list, use the command zypper removerepo together with the alias or number of the repository you want to delete. For example, to remove the repository SLEHA-12-GEO from Example 2.1, “Zypper—List of Known Repositories”, use one of the following commands:

sudo zypper removerepo 1
sudo zypper removerepo "SLEHA-12-GEO" Modifying Repositories

Enable or disable repositories with zypper modifyrepo. You can also alter the repository's properties (such as refreshing behavior, name or priority) with this command. The following command will enable the repository named updates, turn on auto-refresh and set its priority to 20:

sudo zypper modifyrepo -er -p 20 'updates'

Modifying repositories is not limited to a single repository—you can also operate on groups:

-a: all repositories
-l: local repositories
-t: remote repositories
-m TYPE: repositories of a certain type (where TYPE can be one of the following: http, https, ftp, cd, dvd, dir, file, cifs, smb, nfs, hd, iso)

To rename a repository alias, use the renamerepo command. The following example changes the alias from Mozilla Firefox to firefox:

sudo zypper renamerepo 'Mozilla Firefox' firefox

2.1.6 Querying Repositories and Packages with Zypper

Zypper offers various methods to query repositories or packages. To get lists of all products, patterns, packages or patches available, use the following commands:

zypper products
zypper patterns
zypper packages
zypper patches

To query all repositories for certain packages, use search. It works on package names, or, optionally, on package summaries and descriptions. String wrapped in / are interpreted as regular expressions. By default, the search is not case-sensitive.

Simple search for a package name containing fire
zypper search "fire"
Simple search for the exact package MozillaFirefox
zypper search --match-exact "MozillaFirefox"
Also search in package descriptions and summaries
zypper search -d fire
Only display packages not already installed
zypper search -u fire
Display packages containing the string fir not followed be e
zypper se "/fir[^e]/"

To search for packages which provide a special capability, use the command what-provides. For example, if you want to know which package provides the Perl module SVN::Core, use the following command:

zypper what-provides 'perl(SVN::Core)'

To query single packages, use info with an exact package name as an argument. It displays detailed information about a package. To also show what is required/recommended by the package, use the options --requires and --recommends:

zypper info --requires MozillaFirefox

The what-provides PACKAGE_NAME is similar to rpm -q --whatprovides PACKAGE_NAME, but RPM is only able to query the RPM database (that is the database of all installed packages). Zypper, on the other hand, will tell you about providers of the capability from any repository, not only those that are installed.

2.1.7 Configuring Zypper

Zypper now comes with a configuration file, allowing you to permanently change Zypper's behavior (either system-wide or user-specific). For system-wide changes, edit /etc/zypp/zypper.conf. For user-specific changes, edit ~/.zypper.conf. If ~/.zypper.conf does not yet exist, you can use /etc/zypp/zypper.conf as a template: copy it to ~/.zypper.conf and adjust it to your liking. Refer to the comments in the file for help about the available options.

2.1.8 Troubleshooting

In case you have problems to access packages from configured repositories (for example, Zypper cannot find a certain package though you know that it exists in one the repositories), it can help to refresh the repositories with:

sudo zypper refresh

If that does not help, try

sudo zypper refresh -fdb

This forces a complete refresh and rebuild of the database, including a forced download of raw metadata.

2.1.9 Zypper Rollback Feature on Btrfs File System

If the Btrfs file system is used on the root partition and snapper is installed, Zypper automatically calls snapper (via script installed by snapper) when committing changes to the file system to create appropriate file system snapshots. These snapshots can be used for reverting any changes made by Zypper. See Chapter 3, System Recovery and Snapshot Management with Snapper for more information.

2.1.10 For More Information

For more information on managing software from the command line, enter zypper help, zypper help  COMMAND or refer to the zypper(8) man page. For a complete and detailed command reference, including cheat sheets with the most important commands, and information on how to use Zypper in scripts and applications, refer to A list of software changes for the latest openSUSE Leap version can be found at versions.

2.2 RPM—the Package Manager

RPM (RPM Package Manager) is used for managing software packages. Its main commands are rpm and rpmbuild. The powerful RPM database can be queried by the users, system administrators and package builders for detailed information about the installed software.

Essentially, rpm has five modes: installing, uninstalling (or updating) software packages, rebuilding the RPM database, querying RPM bases or individual RPM archives, integrity checking of packages and signing packages. rpmbuild can be used to build installable packages from pristine sources.

Installable RPM archives are packed in a special binary format. These archives consist of the program files to install and certain meta information used during the installation by rpm to configure the software package or stored in the RPM database for documentation purposes. RPM archives normally have the extension .rpm.

Tip: Software Development Packages

For several packages, the components needed for software development (libraries, headers, include files, etc.) have been put into separate packages. These development packages are only needed if you want to compile software yourself (for example, the most recent GNOME packages). They can be identified by the name extension -devel, such as the packages alsa-devel and gimp-devel.

2.2.1 Verifying Package Authenticity

RPM packages have a GPG signature. To verify the signature of an RPM package, use the command rpm --checksig  package-1.2.3.rpm to determine whether the package originates from SUSE or from another trustworthy facility. This is especially recommended for update packages from the Internet.

While fixing issues in the operating system, you might need to install a Problem Temporary Fix (PTF) into a production system. The packages provided by SUSE are signed against a special PTF key. However, in contrast to SUSE Linux Enterprise 11, this key is not imported by default on SUSE Linux Enterprise 12 systems. To manually import the key, use the following command:

rpm --import /usr/share/doc/packages/suse-build-key/suse_ptf_key.asc

After importing the key, you can install PTF packages on your system.

2.2.2 Managing Packages: Install, Update, and Uninstall

Normally, the installation of an RPM archive is quite simple: rpm -i package.rpm. With this command the package is installed, but only if its dependencies are fulfilled and if there are no conflicts with other packages. With an error message, rpm requests those packages that need to be installed to meet dependency requirements. In the background, the RPM database ensures that no conflicts arise—a specific file can only belong to one package. By choosing different options, you can force rpm to ignore these defaults, but this is only for experts. Otherwise, you risk compromising the integrity of the system and possibly jeopardize the ability to update the system.

The options -U or --upgrade and -F or --freshen can be used to update a package (for example, rpm -F package.rpm). This command removes the files of the old version and immediately installs the new files. The difference between the two versions is that -U installs packages that previously did not exist in the system, but -F merely updates previously installed packages. When updating, rpm updates configuration files carefully using the following strategy:

  • If a configuration file was not changed by the system administrator, rpm installs the new version of the appropriate file. No action by the system administrator is required.

  • If a configuration file was changed by the system administrator before the update, rpm saves the changed file with the extension .rpmorig or .rpmsave (backup file) and installs the version from the new package (but only if the originally installed file and the newer version are different). If this is the case, compare the backup file (.rpmorig or .rpmsave) with the newly installed file and make your changes again in the new file. Afterwards, be sure to delete all .rpmorig and .rpmsave files to avoid problems with future updates.

  • .rpmnew files appear if the configuration file already exists and if the noreplace label was specified in the .spec file.

Following an update, .rpmsave and .rpmnew files should be removed after comparing them, so they do not obstruct future updates. The .rpmorig extension is assigned if the file has not previously been recognized by the RPM database.

Otherwise, .rpmsave is used. In other words, .rpmorig results from updating from a foreign format to RPM. .rpmsave results from updating from an older RPM to a newer RPM. .rpmnew does not disclose any information to whether the system administrator has made any changes to the configuration file. A list of these files is available in /var/adm/rpmconfigcheck. Some configuration files (like /etc/httpd/httpd.conf) are not overwritten to allow continued operation.

The -U switch is not just an equivalent to uninstalling with the -e option and installing with the -i option. Use -U whenever possible.

To remove a package, enter rpm -e package. This command only deletes the package if there are no unresolved dependencies. It is theoretically impossible to delete Tcl/Tk, for example, as long as another application requires it. Even in this case, RPM calls for assistance from the database. If such a deletion is, for whatever reason, impossible (even if no additional dependencies exist), it may be helpful to rebuild the RPM database using the option --rebuilddb.

2.2.3 Delta RPM Packages

Delta RPM packages contain the difference between an old and a new version of an RPM package. Applying a delta RPM onto an old RPM results in a completely new RPM. It is not necessary to have a copy of the old RPM because a delta RPM can also work with an installed RPM. The delta RPM packages are even smaller in size than patch RPMs, which is an advantage when transferring update packages over the Internet. The drawback is that update operations with delta RPMs involved consume considerably more CPU cycles than plain or patch RPMs.

The makedeltarpm and applydelta binaries are part of the delta RPM suite (package deltarpm) and help you create and apply delta RPM packages. With the following commands, you can create a delta RPM called The following command assumes that old.rpm and new.rpm are present:

makedeltarpm old.rpm new.rpm

Using applydeltarpm, you can reconstruct the new RPM from the file system if the old package is already installed:

applydeltarpm new.rpm

To derive it from the old RPM without accessing the file system, use the -r option:

applydeltarpm -r old.rpm new.rpm

See /usr/share/doc/packages/deltarpm/README for technical details.

2.2.4 RPM Queries

With the -q option rpm initiates queries, making it possible to inspect an RPM archive (by adding the option -p) and to query the RPM database of installed packages. Several switches are available to specify the type of information required. See Table 2.1, “The Most Important RPM Query Options”.

Table 2.1: The Most Important RPM Query Options


Package information


File list


Query the package that contains the file FILE (the full path must be specified with FILE)


File list with status information (implies -l)


List only documentation files (implies -l)


List only configuration files (implies -l)


File list with complete details (to be used with -l, -c, or -d)


List features of the package that another package can request with --requires

--requires, -R

Capabilities the package requires


Installation scripts (preinstall, postinstall, uninstall)

For example, the command rpm -q -i wget displays the information shown in Example 2.2, “rpm -q -i wget.

Example 2.2: rpm -q -i wget
Name        : wget                         Relocations: (not relocatable)
Version     : 1.11.4                            Vendor: openSUSE
Release     : 1.70                          Build Date: Sat 01 Aug 2009 09:49:48 CEST
Install Date: Thu 06 Aug 2009 14:53:24 CEST      Build Host: build18
Group       : Productivity/Networking/Web/Utilities   Source RPM: wget-1.11.4-1.70.src.rpm
Size        : 1525431                          License: GPL v3 or later
Signature   : RSA/8, Sat 01 Aug 2009 09:50:04 CEST, Key ID b88b2fd43dbdc284
Packager    :
URL         :
Summary     : A Tool for Mirroring FTP and HTTP Servers
Description :
Wget enables you to retrieve WWW documents or FTP files from a server.
This can be done in script files or via the command line.

The option -f only works if you specify the complete file name with its full path. Provide as many file names as desired. For example, the following command

rpm -q -f /bin/rpm /usr/bin/wget

results in:


If only part of the file name is known, use a shell script as shown in Example 2.3, “Script to Search for Packages”. Pass the partial file name to the script shown as a parameter when running it.

Example 2.3: Script to Search for Packages
#! /bin/sh
for i in $(rpm -q -a -l | grep $1); do
    echo "\"$i\" is in package:"
    rpm -q -f $i
    echo ""

The command rpm -q --changelog package displays a detailed list of change information about a specific package, sorted by date.

With the installed RPM database, verification checks can be made. Initiate these with -V, or --verify. With this option, rpm shows all files in a package that have been changed since installation. rpm uses eight character symbols to give some hints about the following changes:

Table 2.2: RPM Verify Options


MD5 check sum


File size


Symbolic link


Modification time


Major and minor device numbers






Mode (permissions and file type)

In the case of configuration files, the letter c is printed. For example, for changes to /etc/wgetrc (wget package):

rpm -V wget
S.5....T c /etc/wgetrc

The files of the RPM database are placed in /var/lib/rpm. If the partition /usr has a size of 1 GB, this database can occupy nearly 30 MB, especially after a complete update. If the database is much larger than expected, it is useful to rebuild the database with the option --rebuilddb. Before doing this, make a backup of the old database. The cron script cron.daily makes daily copies of the database (packed with gzip) and stores them in /var/adm/backup/rpmdb. The number of copies is controlled by the variable MAX_RPMDB_BACKUPS (default: 5) in /etc/sysconfig/backup. The size of a single backup is approximately 1 MB for 1 GB in /usr.

2.2.5 Installing and Compiling Source Packages

All source packages carry a .src.rpm extension (source RPM).

Note: Installed Source Packages

Source packages can be copied from the installation medium to the hard disk and unpacked with YaST. They are not, however, marked as installed ([i]) in the package manager. This is because the source packages are not entered in the RPM database. Only installed operating system software is listed in the RPM database. When you install a source package, only the source code is added to the system.

The following directories must be available for rpm and rpmbuild in /usr/src/packages (unless you specified custom settings in a file like /etc/rpmrc):


for the original sources (.tar.bz2 or .tar.gz files, etc.) and for distribution-specific adjustments (mostly .diff or .patch files)


for the .spec files, similar to a meta Makefile, which control the build process


all the sources are unpacked, patched and compiled in this directory


where the completed binary packages are stored


here are the source RPMs

When you install a source package with YaST, all the necessary components are installed in /usr/src/packages: the sources and the adjustments in SOURCES and the relevant .spec file in SPECS.

Warning: System Integrity

Do not experiment with system components (glibc, rpm, etc.), because this endangers the stability of your system.

The following example uses the wget.src.rpm package. After installing the source package, you should have files similar to those in the following list:


rpmbuild -bX /usr/src/packages/SPECS/wget.spec starts the compilation. X is a wild card for various stages of the build process (see the output of --help or the RPM documentation for details). The following is merely a brief explanation:


Prepare sources in /usr/src/packages/BUILD: unpack and patch.


Do the same as -bp, but with additional compilation.


Do the same as -bp, but with additional installation of the built software. Caution: if the package does not support the BuildRoot feature, you might overwrite configuration files.


Do the same as -bi, but with the additional creation of the binary package. If the compile was successful, the binary should be in /usr/src/packages/RPMS.


Do the same as -bb, but with the additional creation of the source RPM. If the compilation was successful, the binary should be in /usr/src/packages/SRPMS.


Skip some steps.

The binary RPM created can now be installed with rpm -i or, preferably, with rpm -U. Installation with rpm makes it appear in the RPM database.

Keep in mind, the BuildRoot directive in the spec file was deprecated since SLE12 and above. If you still need this feature, use the --buildroot option as a workaround. For a more detailed background, see the support database at

2.2.6 Compiling RPM Packages with build

The danger with many packages is that unwanted files are added to the running system during the build process. To prevent this use build, which creates a defined environment in which the package is built. To establish this chroot environment, the build script must be provided with a complete package tree. This tree can be made available on the hard disk, via NFS, or from DVD. Set the position with build --rpms directory. Unlike rpm, the build command looks for the .spec file in the source directory. To build wget (like in the above example) with the DVD mounted in the system under /media/dvd, use the following commands as root:

cd /usr/src/packages/SOURCES/
mv ../SPECS/wget.spec .
build --rpms /media/dvd/suse/ wget.spec

Subsequently, a minimum environment is established at /var/tmp/build-root. The package is built in this environment. Upon completion, the resulting packages are located in /var/tmp/build-root/usr/src/packages/RPMS.

The build script offers several additional options. For example, cause the script to prefer your own RPMs, omit the initialization of the build environment or limit the rpm command to one of the above-mentioned stages. Access additional information with build --help and by reading the build man page.

2.2.7 Tools for RPM Archives and the RPM Database

Midnight Commander (mc) can display the contents of RPM archives and copy parts of them. It represents archives as virtual file systems, offering all usual menu options of Midnight Commander. Display the HEADER with F3. View the archive structure with the cursor keys and Enter. Copy archive components with F5.

A full-featured package manager is available as a YaST module. For details, see Book “Start-Up”, Chapter 9 “Installing or Removing Software”.

3 System Recovery and Snapshot Management with Snapper


Being able to do file system snapshots providing the ability to do rollbacks on Linux is a feature that was often requested in the past. Snapper, with the Btrfs file system or thin-provisioned LVM volumes now fills that gap.

Btrfs, a new copy-on-write file system for Linux, supports file system snapshots (a copy of the state of a subvolume at a certain point of time) of subvolumes (one or more separately mountable file systems within each physical partition). Snapshots are also supported on thin-provisioned LVM volumes formatted with XFS, Ext4 or Ext3. Snapper lets you create and manage these snapshots. It comes with a command line and a YaST interface. Starting with SUSE Linux Enterprise Server 12 it is also possible to boot from Btrfs snapshots—see Section 3.3, “System Rollback by Booting from Snapshots” for more information.

Using Snapper you can perform the following tasks:

3.1 Default Setup

Snapper on openSUSE Leap is set up to serve as an undo and recovery tool for system changes. By default, the root partition (/) of openSUSE Leap is formatted with Btrfs. Taking snapshots is automatically enabled if the root partition (/) is big enough (approximately more than 16 GB). Taking snapshots on partitions other than / is not enabled by default.

Tip: Enabling Snapper in the Installed System

If you have disabled Snapper during the installation, you can enable it at any time later. To do so, create a default Snapper configuration for the root file system by running

sudo snapper -c root create-config /

Afterward enable the different snapshot types as described in Section, “Disabling/Enabling Snapshots”.

Keep in mind that snapshots require a Btrfs root file system with subvolumes set up as proposed by the installer and a partition size of at least 16 GB.

When a snapshot is created, both the snapshot and the original point to the same blocks in the file system. So, initially a snapshot does not occupy additional disk space. If data in the original file system is modified, changed data blocks are copied while the old data blocks are kept for the snapshot. Therefore, a snapshot occupies the same amount of space as the data modified. So, over time, the amount of space a snapshot allocates, constantly grows. As a consequence, deleting files from a Btrfs file system containing snapshots may not free disk space!

Note: Snapshot Location

Snapshots always reside on the same partition or subvolume on which the snapshot has been taken. It is not possible to store snapshots on a different partition or subvolume.

As a result, partitions containing snapshots need to be larger than normal partitions. The exact amount strongly depends on the number of snapshots you keep and the amount of data modifications. As a rule of thumb you should consider using twice the size than you normally would. To prevent disks from running out of space, old snapshots are automatically cleaned up. Refer to Section, “Controlling Snapshot Archiving” for details.

3.1.1 Types of Snapshots

Although snapshots themselves do not differ in a technical sense, we distinguish between three types of snapshots, based on the occasion on which they were taken:

Timeline Snapshots

A single snapshot is created every hour. Old snapshots are automatically deleted. By default, the first snapshot of the last ten days, months, and years are kept. Timeline snapshots are disabled by default.

Installation Snapshots

Whenever one or more packages are installed with YaST or Zypper, a pair of snapshots is created: one before the installation starts (Pre) and another one after the installation has finished (Post). In case an important system component such as the kernel has been installed, the snapshot pair is marked as important (important=yes). Old snapshots are automatically deleted. By default the last ten important snapshots and the last ten regular (including administration snapshots) snapshots are kept. Installation snapshots are enabled by default.

Administration Snapshots

Whenever you administrate the system with YaST, a pair of snapshots is created: one when a YaST module is started (Pre) and another when the module is closed (Post). Old snapshots are automatically deleted. By default the last ten important snapshots and the last ten regular snapshots (including installation snapshots) are kept. Administration snapshots are enabled by default.

3.1.2 Directories That Are Excluded from Snapshots

Some directories need to be excluded from snapshots for different reasons. The following list shows all directories that are excluded:

/boot/grub2/i386-pc, /boot/grub2/x86_64-efi, /boot/grub2/powerpc-ieee1275, /boot/grub2/s390x-emu

A rollback of the boot loader configuration is not supported. The directories listed above are architecture-specific. The first two directories are present on AMD64/Intel 64 machines, the latter two on IBM POWER and on IBM z Systems, respectively.


If /home does not reside on a separate partition, it is excluded to avoid data loss on rollbacks.

/opt, /var/opt

Third-party products usually get installed to /opt. It is excluded to avoid uninstalling these applications on rollbacks.


Contains data for Web and FTP servers. It is excluded to avoid data loss on rollbacks.

/tmp, /var/tmp, /var/cache, /var/crash

All directories containing temporary files and caches are excluded from snapshots.


This directory is used when manually installing software. It is excluded to avoid uninstalling these installations on rollbacks.


The default location for virtual machine images managed with libvirt. Excluded to ensure virtual machine images are not replaced with older versions during a rollback. By default, this subvolume is created with the option no copy on write.

/var/lib/mailman, /var/spool

Directories containing mails or mail queues are excluded to avoid a loss of mails after a rollback.


Contains zone data for the DNS server. Excluded from snapshots to ensure a name server can operate after a rollback.

/var/lib/mariadb, /var/lib/mysql, /var/lib/pgqsl

These directories contain database data. By default, these subvolumes are created with the option no copy on write.


Log file location. Excluded from snapshots to allow log file analysis after the rollback of a broken system.

3.1.3 Customizing the Setup

openSUSE Leap comes with a reasonable default setup, which should be sufficient for most use cases. However, all aspects of taking automatic snapshots and snapshot keeping can be configured according to your needs. Disabling/Enabling Snapshots

Each of the three snapshot types (timeline, installation, administration) can be enabled or disabled independently.

Disabling/Enabling Timeline Snapshots

Enabling.  snapper-c root set-config "TIMELINE_CREATE=yes"

Disabling.  snapper -c root set-config "TIMELINE_CREATE=no"

Timeline snapshots are enabled by default, except for the root partition.

Disabling/Enabling Installation Snapshots

Enabling:  Install the package snapper-zypp-plugin

Disabling:  Uninstall the package snapper-zypp-plugin

Installation snapshots are enabled by default.

Disabling/Enabling Administration Snapshots

Enabling:  Set USE_SNAPPER to yes in /etc/sysconfig/yast2.

Disabling:  Set USE_SNAPPER to no in /etc/sysconfig/yast2.

Administration snapshots are enabled by default. Controlling Installation Snapshots

Taking snapshot pairs upon installing packages with YaST or Zypper is handled by the snapper-zypp-plugin. An XML configuration file, /etc/snapper/zypp-plugin.conf defines, when to make snapshots. By default the file looks like the following:

 1 <?xml version="1.0" encoding="utf-8"?>
 2 <snapper-zypp-plugin-conf>
 3  <solvables>
 4   <solvable match="w"1 important="true"2>kernel-*3</solvable>
 5   <solvable match="w" important="true">dracut</solvable>
 6   <solvable match="w" important="true">glibc</solvable>
 7   <solvable match="w" important="true">systemd*</solvable>
 8   <solvable match="w" important="true">udev</solvable>
 9   <solvable match="w">*</solvable>4
10  </solvables>
11 </snapper-zypp-plugin-conf>


The match attribute defines whether the pattern is a Unix shell-style wild card (w) or a Python regular expression (re).


If the given pattern matches and the corresponding package is marked as important (for example Kernel packages), the snapshot will also be marked as important.


Pattern to match a package name. Based on the setting of the match attribute, special characters are either interpreted as shell wild cards or regular expressions. This pattern matches all package names starting with kernel-.


This line unconditionally matches all packages.

With this configuration snapshot, pairs are made whenever a package is installed (line 9). When Kernel, dracut, glibc, systemd, or udev packages marked as important are installed, the snapshot pair will also be marked as important (lines 4 to 8). All rules are evaluated.

To disable a rule, either delete it or deactivate it using XML comments. To prevent the system from making snapshot pairs for every package installation for example, comment line 9:

 1 <?xml version="1.0" encoding="utf-8"?>
 2 <snapper-zypp-plugin-conf>
 3  <solvables>
 4   <solvable match="w" important="true">kernel-*</solvable>
 5   <solvable match="w" important="true">dracut</solvable>
 6   <solvable match="w" important="true">glibc</solvable>
 7   <solvable match="w" important="true">systemd*</solvable>
 8   <solvable match="w" important="true">udev</solvable>
 9   <!-- <solvable match="w">*</solvable> -->
10  </solvables>
11 </snapper-zypp-plugin-conf> Creating and Mounting New Subvolumes

Creating a new subvolume underneath the /-hierarchy and permanently mounting it is supported. However, you need to make sure not to create it inside a snapshot, since you would not be able to delete snapshots anymore after a rollback.

openSUSE Leap is configured with the /@/ subvolume which serves as an independent root for permanent subvolumes such as /opt, /srv, /home and others. Any new subvolumes you create and permanently mount need to be created in this initial root file system.

To do so, run the following commands. In this example, a new subvolume /usr/important is created from /dev/sda2.

mount /dev/sda2 -o subvol=@ /mnt
btrfs subvolume create /mnt/usr/important
umount /mnt

The corresponding entry in /etc/fstab needs to look like the following:

/dev/sda2 /usr/important btrfs subvol=@/usr/important 0 0 Controlling Snapshot Archiving

Snapshots occupy disk space. To prevent disks from running out of space and thus causing system outages, old snapshots are automatically deleted. By default, up to ten important installation and administration snapshots and up to ten regular installation and administration snapshots are kept. If these snapshots occupy more than 50% of the root file system size, additional snapshots will be deleted. A minimum of four important and two regular snapshots are always kept.

Refer to Section 3.4.1, “Managing Existing Configurations” for instructions on how to change these values. Using Snapper on Thin-Provisioned LVM Volumes

Apart from snapshots on Btrfs file systems, Snapper also supports taking snapshots on thin-provisioned LVM volumes (snapshots on regular LVM volumes are not supported) formatted with XFS, Ext4 or Ext3. For more information and setup instructions on LVM volumes, refer to Section 5.2, “LVM Configuration”.

To use Snapper on a thin-provisioned LVM volume you need to create a Snapper configuration for it. On LVM it is required to specify the file system with --fstype=lvm(FILESYSTEM). ext3, etx4 or xfs are valid values for FILESYSTEM. Example:

snapper -c lvm create-config --fstype="lvm(xfs)" /thin_lvm

You can adjust this configuration according to your needs as described in Section 3.4.1, “Managing Existing Configurations”.

3.2 Using Snapper to Undo Changes

Snapper on openSUSE Leap is preconfigured to serve as a tool that lets you undo changes made by zypper and YaST. For this purpose, Snapper is configured to create a pair of snapshots before and after each run of zypper and YaST. Snapper also lets you restore system files that have been accidentally deleted or modified. Timeline snapshots for the root partition need to be enabled for this purpose—see Section, “Disabling/Enabling Snapshots” for details.

By default, automatic snapshots as described above are configured for the root partition and its subvolumes. To make snapshots available for other partitions such as /home for example, you can create custom configurations.

Important: Undoing Changes Compared to Rollback

When working with snapshots to restore data, it is important to know that there are two fundamentally different scenarios Snapper can handle:

Undoing Changes

When undoing changes as described in the following, two snapshots are being compared and the changes between these two snapshots are made undone. Using this method also allows to explicitly select the files that should be restored.


When doing rollbacks as described in Section 3.3, “System Rollback by Booting from Snapshots”, the system is reset to the state at which the snapshot was taken.

When undoing changes, it is also possible to compare a snapshot against the current system. When restoring all files from such a comparison, this will have the same result as doing a rollback. However, using the method described in Section 3.3, “System Rollback by Booting from Snapshots” for rollbacks should be preferred, since it is faster and allows you to review the system before doing the rollback.

Warning: Data Consistency

There is no mechanism to ensure data consistency when creating a snapshot. Whenever a file (for example, a database) is written at the same time as the snapshot is being created, it will result in a broken or partly written file. Restoring such a file will cause problems. Furthermore, some system files such as /etc/mtab must never be restored. Therefore it is strongly recommended to always closely review the list of changed files and their diffs. Only restore files that really belong to the action you want to revert.

3.2.1 Undoing YaST and Zypper Changes

If you set up the root partition with Btrfs during the installation, Snapper—preconfigured for doing rollbacks of YaST or Zypper changes—will automatically be installed. Every time you start a YaST module or a Zypper transaction, two snapshots are created: a pre-snapshot capturing the state of the file system before the start of the module and a post-snapshot after the module has been finished.

Using the YaST Snapper module or the snapper command line tool, you can undo the changes made by YaST/Zypper by restoring files from the pre-snapshot. Comparing two snapshots the tools also allow you to see which files have been changed. You can also display the differences between two versions of a file (diff).

Procedure 3.1: Undoing Changes Using the YaST Snapper Module
  1. Start the Snapper module from the Miscellaneous section in YaST or by entering yast2 snapper.

  2. Make sure Current Configuration is set to root. This is always the case unless you have manually added own Snapper configurations.

  3. Choose a pair of pre- and post-snapshots from the list. Both, YaST and Zypper snapshot pairs are of the type Pre & Post. YaST snapshots are labeled as zypp(y2base) in the Description column; Zypper snapshots are labeled zypp(zypper).

  4. Click Show Changes to open the list of files that differ between the two snapshots.

  5. Review the list of files. To display a diff between the pre- and post-version of a file, select it from the list.

  6. To restore one or more files, select the relevant files or directories by activating the respective check box. Click Restore Selected and confirm the action by clicking Yes.

    To restore a single file, activate its diff view by clicking its name. Click Restore From First and confirm your choice with Yes.

Procedure 3.2: Undoing Changes Using the snapper Command
  1. Get a list of YaST and Zypper snapshots by running snapper list -t pre-post. YaST snapshots are labeled as yast module_name in the Description column; Zypper snapshots are labeled zypp(zypper).

    root # snapper list -t pre-post
    Pre # | Post # | Pre Date                      | Post Date                     | Description
    311   | 312    | Tue 06 May 2014 14:05:46 CEST | Tue 06 May 2014 14:05:52 CEST | zypp(y2base)
    340   | 341    | Wed 07 May 2014 16:15:10 CEST | Wed 07 May 2014 16:15:16 CEST | zypp(zypper)
    342   | 343    | Wed 07 May 2014 16:20:38 CEST | Wed 07 May 2014 16:20:42 CEST | zypp(y2base)
    344   | 345    | Wed 07 May 2014 16:21:23 CEST | Wed 07 May 2014 16:21:24 CEST | zypp(zypper)
    346   | 347    | Wed 07 May 2014 16:41:06 CEST | Wed 07 May 2014 16:41:10 CEST | zypp(y2base)
    348   | 349    | Wed 07 May 2014 16:44:50 CEST | Wed 07 May 2014 16:44:53 CEST | zypp(y2base)
    350   | 351    | Wed 07 May 2014 16:46:27 CEST | Wed 07 May 2014 16:46:38 CEST | zypp(y2base)
  2. Get a list of changed files for a snapshot pair with snapper status PRE..POST. Files with content changes are marked with c, files that have been added are marked with + and deleted files are marked with -.

    root # snapper status 350..351
    +..... /usr/share/doc/packages/mikachan-fonts
    +..... /usr/share/doc/packages/mikachan-fonts/COPYING
    +..... /usr/share/doc/packages/mikachan-fonts/dl.html
    c..... /usr/share/fonts/truetype/fonts.dir
    c..... /usr/share/fonts/truetype/fonts.scale
    +..... /usr/share/fonts/truetype/みかちゃん-p.ttf
    +..... /usr/share/fonts/truetype/みかちゃん-pb.ttf
    +..... /usr/share/fonts/truetype/みかちゃん-ps.ttf
    +..... /usr/share/fonts/truetype/みかちゃん.ttf
    c..... /var/cache/fontconfig/7ef2298fde41cc6eeb7af42e48b7d293-x86_64.cache-4
    c..... /var/lib/rpm/Basenames
    c..... /var/lib/rpm/Dirnames
    c..... /var/lib/rpm/Group
    c..... /var/lib/rpm/Installtid
    c..... /var/lib/rpm/Name
    c..... /var/lib/rpm/Packages
    c..... /var/lib/rpm/Providename
    c..... /var/lib/rpm/Requirename
    c..... /var/lib/rpm/Sha1header
    c..... /var/lib/rpm/Sigmd5
  3. To display the diff for a certain file, run snapper diff PRE..POST FILENAME. If you do not specify FILENAME, a diff for all files will be displayed.

    root # snapper diff 350..351 /usr/share/fonts/truetype/fonts.scale
    --- /.snapshots/350/snapshot/usr/share/fonts/truetype/fonts.scale       2014-04-23 15:58:57.000000000 +0200
    +++ /.snapshots/351/snapshot/usr/share/fonts/truetype/fonts.scale       2014-05-07 16:46:31.000000000 +0200
    @@ -1,4 +1,4 @@
     ds=y:ai=0.2:luximr.ttf -b&h-luxi mono-bold-i-normal--0-0-0-0-c-0-iso10646-1
     ds=y:ai=0.2:luximr.ttf -b&h-luxi mono-bold-i-normal--0-0-0-0-c-0-iso8859-1
  4. To restore one or more files run snapper -v undochange PRE..POST FILENAMES. If you do not specify a FILENAMES, all changed files will be restored.

    root # snapper -v undochange 350..351
         create:0 modify:13 delete:7
         undoing change...
         deleting /usr/share/doc/packages/mikachan-fonts
         deleting /usr/share/doc/packages/mikachan-fonts/COPYING
         deleting /usr/share/doc/packages/mikachan-fonts/dl.html
         deleting /usr/share/fonts/truetype/みかちゃん-p.ttf
         deleting /usr/share/fonts/truetype/みかちゃん-pb.ttf
         deleting /usr/share/fonts/truetype/みかちゃん-ps.ttf
         deleting /usr/share/fonts/truetype/みかちゃん.ttf
         modifying /usr/share/fonts/truetype/fonts.dir
         modifying /usr/share/fonts/truetype/fonts.scale
         modifying /var/cache/fontconfig/7ef2298fde41cc6eeb7af42e48b7d293-x86_64.cache-4
         modifying /var/lib/rpm/Basenames
         modifying /var/lib/rpm/Dirnames
         modifying /var/lib/rpm/Group
         modifying /var/lib/rpm/Installtid
         modifying /var/lib/rpm/Name
         modifying /var/lib/rpm/Packages
         modifying /var/lib/rpm/Providename
         modifying /var/lib/rpm/Requirename
         modifying /var/lib/rpm/Sha1header
         modifying /var/lib/rpm/Sigmd5
         undoing change done
Warning: Reverting User Additions

Reverting user additions via undoing changes with Snapper is not recommended. Since certain directories are excluded from snapshots, files belonging to these users will remain in the file system. If a user with the same user ID as a deleted user is created, this user will inherit the files. Therefore it is strongly recommended to use the YaST User and Group Management tool to remove users.

3.2.2 Using Snapper to Restore Files

Apart from the installation and administration snapshots, Snapper creates timeline snapshots. You can use these backup snapshots to restore files that have accidentally been deleted or to restore a previous version of a file. By using Snapper's diff feature you can also find out which modifications have been made at a certain point of time.

Being able to restore files is especially interesting for data, which may reside on subvolumes or partitions for which snapshots are not taken by default. To be able to restore files from home directories, for example, create a separate Snapper configuration for /home doing automatic timeline snapshots. See Section 3.4, “Creating and Modifying Snapper Configurations” for instructions.

Warning: Restoring Files Compared to Rollback

Snapshots taken from the root file system (defined by Snapper's root configuration), can be used to do a system rollback. The recommended way to do such a rollback is to boot from the snapshot and then perform the rollback. See Section 3.3, “System Rollback by Booting from Snapshots” for details.

Performing a rollback would also be possible by restoring all files from a root file system snapshot as described below. However, this is not recommended. You may restore single files, for example a configuration file from the /etc directory, but not the complete list of files from the snapshot.

This restriction only affects snapshots taken from the root file system!

Procedure 3.3: Restoring Files Using the YaST Snapper Module
  1. Start the Snapper module from the Miscellaneous section in YaST or by entering yast2 snapper.

  2. Choose the Current Configuration from which to choose a snapshot.

  3. Select a timeline snapshot from which to restore a file and choose Show Changes. Timeline snapshots are of the type Single with a description value of timeline.

  4. Select a file from the text box by clicking the file name. The difference between the snapshot version and the current system is shown. Activate the check box to select the file for restore. Do so for all files you want to restore.

  5. Click Restore Selected and confirm the action by clicking Yes.

Procedure 3.4: Restoring Files Using the snapper Command
  1. Get a list of timeline snapshots for a specific configuration by running the following command:

    snapper -c CONFIG list -t single | grep timeline

    CONFIG needs to be replaced by an existing Snapper configuration. Use snapper list-configs to display a list.

  2. Get a list of changed files for a given snapshot by running the following command:

    snapper -c CONFIG status SNAPSHOT_ID..0

    Replace SNAPSHOT_ID by the ID for the snapshot from which you want to restore the file(s).

  3. Optionally list the differences between the current file version and the one from the snapshot by running

    snapper -c CONFIG diff SNAPSHOT_ID..0 FILE NAME

    If you do not specify <FILE NAME>, the difference for all files are shown.

  4. To restore one or more files, run

    snapper -c CONFIG -v undochange

    If you do not specify file names, all changed files will be restored.

3.3 System Rollback by Booting from Snapshots

The GRUB 2 version included on openSUSE Leap can boot from Btrfs snapshots. Together with Snapper's rollback feature, this allows to recover a misconfigured system. Only snapshots created for the default Snapper configuration (root) are bootable.

Important: Supported Configuration

As of openSUSE Leap 42.2 system rollbacks are only supported if the default subvolume configuration of the root partition has not been changed.

When booting a snapshot, the parts of the file system included in the snapshot are mounted read-only; all other file systems and parts that are excluded from snapshots are mounted read-write and can be modified.

Important: Undoing Changes Compared to Rollback

When working with snapshots to restore data, it is important to know that there are two fundamentally different scenarios Snapper can handle:

Undoing Changes

When undoing changes as described in Section 3.2, “Using Snapper to Undo Changes”, two snapshots are compared and the changes between these two snapshots are reverted. Using this method also allows to explicitly exclude selected files from being restored.


When doing rollbacks as described in the following, the system is reset to the state at which the snapshot was taken.

To do a rollback from a bootable snapshot, the following requirements must be met. When doing a default installation, the system is set up accordingly.

Requirements for a Rollback from a Bootable Snapshot
  • The root file system needs to be Btrfs. Booting from LVM volume snapshots is not supported.

  • The root file system needs to be on a single device, a single partition and a single subvolume. Directories that are excluded from snapshots such as /srv (see Section 3.1.2, “Directories That Are Excluded from Snapshots” for a full list) may reside on separate partitions.

  • The system needs to be bootable via the installed boot loader.

To perform a rollback from a bootable snapshot, do as follows:

  1. Boot the system. In the boot menu choose Bootable snapshots and select the snapshot you want to boot. The list of snapshots is listed by date—the most recent snapshot is listed first.

  2. Log in to the system. Carefully check whether everything works as expected. Note that you cannot write to any directory that is part of the snapshot. Data you write to other directories will not get lost, regardless of what you do next.

  3. Depending on whether you want to perform the rollback or not, choose your next step:

    1. If the system is in a state where you do not want to do a rollback, reboot to boot into the current system state, to choose a different snapshot, or to start the rescue system.

    2. If you want to perform the rollback, run

      sudo snapper rollback

      and reboot afterward. On the boot screen, choose the default boot entry to reboot into the reinstated system.

Tip: Rolling Back to a Specific Installation State

If snapshots are not disabled during installation, an initial bootable snapshot is created at the end of the initial system installation. You can go back to that state at any time by booting this snapshot. The snapshot can be identified by the description after installation.

A bootable snapshot is also created when starting a system upgrade to a service pack or a new major release (provided snapshots are not disabled).

3.3.1 Accessing and Identifying Snapshot Boot Entries

To boot from a snapshot, reboot your machine and choose Start Bootloader from a read-only snapshot. A screen listing all bootable snapshots opens. The most recent snapshot is listed first, the oldest last. Use the keys and to navigate and press Enter to activate the selected snapshot. Activating a snapshot from the boot menu does not reboot the machine immediately, but rather opens the boot loader of the selected snapshot.

Boot Loader: Snapshots
Figure 3.1: Boot Loader: Snapshots

Each snapshot entry in the boot loader follows a naming scheme which makes it possible to identify it easily:



If the snapshot was marked important, the entry is marked with a *.


Operating system label.


Date in the format YYYY-MM-DD.


Time in the format HH:MM.


This field contains a description of the snapshot. In case of a manually created snapshot this is the string created with the option --description or a custom string (see Tip: Setting a Custom Description for Boot Loader Snapshot Entries). In case of an automatically created snapshot, it is the tool that was called, for example zypp(zypper) or yast_sw_single. Long descriptions may be truncated, depending on the size of the boot screen.

Tip: Setting a Custom Description for Boot Loader Snapshot Entries

It is possible to replace the default string in the description field of a snapshot with a custom string. This is for example useful if an automatically created description is not sufficient, or a user-provided description is too long. To set a custom string STRING for snapshot NUMBER, use the following command:

snapper modify --userdata "bootloader=STRING" NUMBER

The description should be no longer than 25 characters—everything that exceeds this size will not be readable on the boot screen.

3.3.2 Limitations

A complete system rollback, restoring the complete system to the identical state as it was in when a snapshot was taken, is not possible. Directories Excluded from Snapshots

Root file system snapshots do not contain all directories. See Section 3.1.2, “Directories That Are Excluded from Snapshots” for details and reasons. As a general consequence, data from these directories is not restored, resulting in the following limitations.

Add-ons and Third Party Software may be Unusable after a Rollback

Applications and add-ons installing data in subvolumes excluded from the snapshot, such as /opt, may not work after a rollback, if others parts of the application data are also installed on subvolumes included in the snapshot. Re-install the application or the add-on to solve this problem.

File Access Problems

If an application had changed file permissions and/or ownership in between snapshot and current system, the application may not be able to access these files. Reset permissions and/or ownership for the affected files after the rollback.

Incompatible Data Formats

If a service or an application has established a new data format in between snapshot and current system, the application may not be able to read the affected data files after a rollback.

Subvolumes with a Mixture of Code and Data

Subvolumes like /srv may contain a mixture of code and data. A rollback may result in non-functional code. A downgrade of the PHP version, for example, may result in broken PHP scripts for the Web server.

User Data

If a rollback removes users from the system, data that is owned by these users in directories excluded from the snapshot, is not removed. If a user with the same user ID is created, this user will inherit the files. Use a tool like find to locate and remove orphaned files. No Rollback of Boot Loader Data

A rollback of the boot loader is not possible, since all stages of the boot loader must fit together. This cannot be guaranteed when doing rollbacks of /boot.

3.4 Creating and Modifying Snapper Configurations

The way Snapper behaves is defined in a configuration file that is specific for each partition or Btrfs subvolume. These configuration files reside under /etc/snapper/configs/.

In case the root file system is big enough (approximately 16 GB), snapshots are automatically enabled for the root file system / upon the installation. The corresponding default configuration is named root. It creates and manages the YaST and Zypper snapshot. See Section, “Configuration Data” for a list of the default values.

You may create your own configurations for other partitions formatted with Btrfs or existing subvolumes on a Btrfs partition. In the following example we will set up a Snapper configuration for backing up the Web server data residing on a separate, Btrfs-formatted partition mounted at /srv/www.

After a configuration has been created, you can either use snapper itself or the YaST Snapper module to restore files from these snapshots. In YaST you need to select your Current Configuration, while you need to specify your configuration for snapper with the global switch -c (for example, snapper -c myconfig list).

To create a new Snapper configuration, run snapper create-config:

snapper -c www-data1 create-config /srv/www2


Name of configuration file.


Mount point of the partition or Btrfs subvolume on which to take snapshots.

This command will create a new configuration file /etc/snapper/configs/www-data with reasonable default values (taken from /etc/snapper/config-templates/default). Refer to Section 3.4.1, “Managing Existing Configurations” for instructions on how to adjust these defaults.

Tip: Configuration Defaults

Default values for a new configuration are taken from /etc/snapper/config-templates/default. To use your own set of defaults, create a copy of this file in the same directory and adjust it to your needs. To use it, specify the -t option with the create-config command:

snapper -c www-data create-config -t my_defaults /srv/www

3.4.1 Managing Existing Configurations

The snapper offers several subcommands for managing existing configurations. You can list, show, delete and modify them:

List Configurations

Use the command snapper list-configs to get all existing configurations:

root # snapper list-configs
Config | Subvolume
root   | /
usr    | /usr
local  | /local
Show a Configuration

Use the subcommand snapper -c CONFIG get-config to display the specified configuration. Config needs to be replaced by a configuration name shown by snapper list-configs. See Section, “Configuration Data” for more information on the configuration options.

To display the default configuration run

snapper -c root get-config
Modify a Configuration

Use the subcommand snapper -c CONFIG set-config OPTION=VALUE to modify an option in the specified configuration. Config needs to be replaced by a configuration name shown by snapper list-configs. Possible values for OPTION and VALUE are listed in Section, “Configuration Data”.

Delete a Configuration

Use the subcommand snapper -c CONFIG delete-config to delete a configuration. Config needs to be replaced by a configuration name shown by snapper list-configs. Configuration Data

Each configuration contains a list of options that can be modified from the command line. The following list provides details for each option. To change a value, run snapper -c CONFIG set-config "KEY=VALUE".


Granting permissions to use snapshots to regular users. See Section, “Using Snapper as Regular User” for more information.

The default value is "".


Defines whether pre and post snapshots should be compared in the background after creation.

The default value is "yes".


Defines the clean-up algorithm for snapshots pairs with identical pre and post snapshots. See Section 3.6.3, “Cleaning Up Snapshot Pairs That Do Not Differ” for details.


File system type of the partition. Do not change.

The default value is "btrfs".


Defines the clean-up algorithm for installation and admin snapshots. See Section 3.6.1, “Cleaning Up Numbered Snapshots” for details.


Adds quota support to the clean-up algorithms. See Section 3.6.5, “Adding Disk Quota Support” for details.


Mount point of the partition or subvolume to snapshot. Do not change.

The default value is "/".


If Snapper is to be used by regular users (see Section, “Using Snapper as Regular User”) the users must be able to access the .snapshot directories and to read files within them. If SYNC_ACL is set to yes, Snapper automatically makes them accessible using ACLs for users and groups from the ALLOW_USERS or ALLOW_GROUPS entries.

The default value is "no".


If set to yes, hourly snapshots are created. Valid values: yes, no.

The default value is "no".


Defines the clean-up algorithm for timeline snapshots. See Section 3.6.2, “Cleaning Up Timeline Screenshots” for details. Using Snapper as Regular User

By default Snapper can only be used by root. However, there are cases in which certain groups or users need to be able to create snapshots or undo changes by reverting to a snapshot:

  • Web site administrators who want to take snapshots of /srv/www

  • Users who want to take a snapshot of their home directory

For these purposes Snapper configurations that grant permissions to users or/and groups can be created. The corresponding .snapshots directory needs to be readable and accessible by the specified users. The easiest way to achieve this is to set the SYNC_ACL option to yes.

Procedure 3.5: Enabling Regular Users to Use Snapper

Note that all steps in this procedure need to be run by root.

  1. If not existing, create a Snapper configuration for the partition or subvolume on which the user should be able to use Snapper. Refer to Section 3.4, “Creating and Modifying Snapper Configurations” for instructions. Example:

    snapper --config web_data create /srv/www
  2. The configuration file is created under /etc/snapper/configs/CONFIG, where CONFIG is the value you specified with -c/--config in the previous step (for example /etc/snapper/configs/web_data). Adjust it according to your needs; see Section 3.4.1, “Managing Existing Configurations” for details.

  3. Set values for ALLOW_USERS and/or ALLOW_GROUPS to grant permissions to users and/or groups, respectively. Multiple entries need to be separated by Space. To grant permissions to the user www_admin for example, run:

    snapper -c web_data set-config "ALLOW_USERS=www_admin" SYNC_ACL="yes"
  4. The given Snapper configuration can now be used by the specified user(s) and/or group(s). You can test it with the list command, for example:

    www_admin:~ > snapper -c web_data list

3.5 Manually Creating and Managing Snapshots

Snapper is not restricted to creating and managing snapshots automatically by configuration; you can also create snapshot pairs (before and after) or single snapshots manually using either the command line tool or the YaST module.

All Snapper operations are carried out for an existing configuration (see Section 3.4, “Creating and Modifying Snapper Configurations” for details). You can only take snapshots of partitions or volumes for which a configuration exists. By default the system configuration (root) is used. If you want to create or manage snapshots for your own configuration you need to explicitly choose it. Use the Current Configuration drop-down box in YaST or specify the -c on the command line (snapper -c MYCONFIG COMMAND).

3.5.1 Snapshot Metadata

Each snapshot consists of the snapshot itself and some metadata. When creating a snapshot you also need to specify the metadata. Modifying a snapshot means changing its metadata—you cannot modify its content. Use snapper list to show existing snapshots and their metadata:

snapper --config home list

Lists snapshots for the configuration home. To list snapshots for the default configuration (root), use snapper -c root list or snapper list.

snapper list -a

Lists snapshots for all existing configurations.

snapper list -t pre-post

Lists all pre and post snapshot pairs for the default (root) configuration.

snapper list -t single

Lists all snapshots of the type single for the default (root) configuration.

The following metadata is available for each snapshot:

  • Type: Snapshot type, see Section, “Snapshot Types” for details. This data cannot be changed.

  • Number: Unique number of the snapshot. This data cannot be changed.

  • Pre Number: Specifies the number of the corresponding pre snapshot. For snapshots of type post only. This data cannot be changed.

  • Description: A description of the snapshot.

  • Userdata: An extended description where you can specify custom data in the form of a comma-separated key=value list: reason=testing, project=foo. This field is also used to mark a snapshot as important (important=yes) and to list the user that created the snapshot (user=tux).

  • Cleanup-Algorithm: Cleanup-algorithm for the snapshot, see Section 3.6, “Automatic Snapshot Clean-Up” for details. Snapshot Types

Snapper knows three different types of snapshots: pre, post, and single. Physically they do not differ, but Snapper handles them differently.


Snapshot of a file system before a modification. Each pre snapshot has got a corresponding post snapshot. Used for the automatic YaST/Zypper snapshots, for example.


Snapshot of a file system after a modification. Each post snapshot has got a corresponding pre snapshot. Used for the automatic YaST/Zypper snapshots, for example.


Stand-alone snapshot. Used for the automatic hourly snapshots, for example. This is the default type when creating snapshots. Cleanup-algorithms

Snapper provides three algorithms to clean up old snapshots. The algorithms are executed in a daily cron-job. It is possible to define the number of different types of snapshots to keep in the Snapper configuration (see Section 3.4.1, “Managing Existing Configurations” for details).


Deletes old snapshots when a certain snapshot count is reached.


Deletes old snapshots having passed a certain age, but keeps several hourly, daily, monthly, and yearly snapshots.


Deletes pre/post snapshot pairs with empty diffs.

3.5.2 Creating Snapshots

Creating a snapshot is done by running snapper create or by clicking Create in the YaST module Snapper. The following examples explain how to create snapshots from the command line. It should be easy to adopt them when using the YaST interface.

Tip: Snapshot Description

You should always specify a meaningful description to later be able to identify its purpose. Even more information can be specified via the user data option.

snapper create --description "Snapshot for week 2 2014"

Creates a stand-alone snapshot (type single) for the default (root) configuration with a description. Because no cleanup-algorithm is specified, the snapshot will never be deleted automatically.

snapper --config home create --description "Cleanup in ~tux"

Creates a stand-alone snapshot (type single) for a custom configuration named home with a description. Because no cleanup-algorithm is specified, the snapshot will never be deleted automatically.

snapper --config home create --description "Daily data backup" --cleanup-algorithm timeline>

Creates a stand-alone snapshot (type single) for a custom configuration named home with a description. The file will automatically be deleted when it meets the criteria specified for the timeline cleanup-algorithm in the configuration.

snapper create --type pre --print-number --description "Before the Apache config cleanup" --userdata "important=yes"

Creates a snapshot of the type pre and prints the snapshot number. First command needed to create a pair of snapshots used to save a before and after state. The snapshot is marked as important.

snapper create --type post --pre-number 30 --description "After the Apache config cleanup" --userdata "important=yes"

Creates a snapshot of the type post paired with the pre snapshot number 30. Second command needed to create a pair of snapshots used to save a before and after state. The snapshot is marked as important.

snapper create --command COMMAND --description "Before and after COMMAND"

Automatically creates a snapshot pair before and after running COMMAND. This option is only available when using snapper on the command line.

3.5.3 Modifying Snapshot Metadata

Snapper allows you to modify the description, the cleanup algorithm, and the user data of a snapshot. All other metadata cannot be changed. The following examples explain how to modify snapshots from the command line. It should be easy to adopt them when using the YaST interface.

To modify a snapshot on the command line, you need to know its number. Use snapper list to display all snapshots and their numbers.

The YaST Snapper module already lists all snapshots. Choose one from the list and click Modify.

snapper modify --cleanup-algorithm "timeline" 10

Modifies the metadata of snapshot 10 for the default (root) configuration. The cleanup algorithm is set to timeline.

snapper --config home modify --description "daily backup" -cleanup-algorithm "timeline" 120

Modifies the metadata of snapshot 120 for a custom configuration named home. A new description is set and the cleanup algorithm is unset.

3.5.4 Deleting Snapshots

To delete a snapshot with the YaST Snapper module, choose a snapshot from the list and click Delete.

To delete a snapshot with the command line tool, you need to know its number. Get it by running snapper list. To delete a snapshot, run snapper delete NUMBER.

When deleting snapshots with Snapper, the freed space will be claimed by a Btrfs process running in the background. Thus the visibility and the availability of free space is delayed. In case you need space freed by deleting a snapshot to be available immediately, use the option --sync with the delete command.

Tip: Deleting Snapshot Pairs

When deleting a pre snapshot, you should always delete its corresponding post snapshot (and vice versa).

snapper delete 65

Deletes snapshot 65 for the default (root) configuration.

snapper -c home delete 89 90

Deletes snapshots 89 and 90 for a custom configuration named home.

snapper delete --sync 23

Deletes snapshot 23 for the default (root) configuration and makes the freed space available immediately.

Tip: Delete Unreferenced Snapshots

Sometimes the Btrfs snapshot is present but the XML file containing the metadata for Snapper is missing. In this case the snapshot is not visible for Snapper and needs to be deleted manually:

btrfs subvolume delete /.snapshots/SNAPSHOTNUMBER/snapshot
rm -rf /.snapshots/SNAPSHOTNUMBER
Tip: Old Snapshots Occupy More Disk Space

If you delete snapshots to free space on your hard disk, make sure to delete old snapshots first. The older a snapshot is, the more disk space it occupies.

Snapshots are also automatically deleted by a daily cron-job. Refer to Section, “Cleanup-algorithms” for details.

3.6 Automatic Snapshot Clean-Up

Snapshots occupy disk space and over time the amount of disk space occupied by the snapshots may become large. To prevent disks from running out of space, Snapper offers algorithms to automatically delete old snapshots. These algorithms differentiate between timeline snapshots and numbered snapshots (administration plus installation snapshot pairs). You can specify the number of snapshots to keep for each type.

In addition to that, you can optionally specify a disk space quota, defining the maximum amount of disk space the snapshots may occupy. It is also possible to automatically delete pre and post snapshots pairs that do not differ.

A clean-up algorithm is always bound to a single Snapper configuration, so you need to configure algorithms for each configuration. In case you want to prevent certain snapshots from being automatically deleted, refer to How to make a snapshot permanent? .

The default setup (root) is configured to do clean-up for numbered snapshots and empty pre and post snapshot pairs. Quota support is enabled—snapshots may not occupy more than 50% of the available disk space of the root partition. Timeline snapshots are disabled by default, therefore the timeline clean-up algorithm is also disabled.

3.6.1 Cleaning Up Numbered Snapshots

Cleaning up for numbered snapshots—administration plus installation snapshot pairs—is controlled by the following parameters of a Snapper configuration.


Enables or disables clean-up of installation and admin snapshot pairs. If enabled, snapshot pairs are deleted when the total snapshot count exceeds a number specified with NUMBER_LIMIT and/or NUMBER_LIMIT_IMPORTANT and an age specified with NUMBER_MIN_AGE. Valid values: yes (enable), no (disable).

The default value is "yes".

Example command to change or set:

snapper -c CONFIG set-config "NUMBER_CLEANUP=no"

Defines how many regular and/or important installation and administration snapshot pairs to keep. Only the youngest snapshots will be kept. Ignored if NUMBER_CLEANUP is set to "no".

The default value is "2-10" for NUMBER_LIMIT and "4-10" for NUMBER_LIMIT_IMPORTANT.

Example command to change or set:

snapper -c CONFIG set-config "NUMBER_LIMIT=10"
Important: Ranged Compared to Constant Values

In case quota support is enabled (see Section 3.6.5, “Adding Disk Quota Support”) the limit needs to be specified as a minimum-maximum range, for example 2-10. If quota support is disabled, a constant value, for example 10, needs to be provided, otherwise cleaning-up will fail with an error.


Defines the minimum age in seconds a snapshot must have before it can automatically be deleted. Snapshots younger than the value specified here will not be deleted, regardless of how many exist.

The default value is "1800".

Example command to change or set:

snapper -c CONFIG set-config "NUMBER_MIN_AGE=864000"
Note: Limit and Age

NUMBER_LIMIT, NUMBER_LIMIT_IMPORTANT and NUMBER_MIN_AGE are always evaluated. Snapshots are only deleted when all conditions are met.

If you always want to keep the number of snapshots defined with NUMBER_LIMIT* regardless of their age, set NUMBER_MIN_AGE to 0.

Example 3.1: Keep the Last 10 Important and Regular Snapshots Regardless of Age

On the other hand, if you do not want to keep snapshots beyond a certain age, set NUMBER_LIMIT* to 0 and provide the age with NUMBER_MIN_AGE.

Example 3.2: Only Keep Snapshots Younger Than Ten Days

3.6.2 Cleaning Up Timeline Screenshots

Cleaning up for timeline snapshots is controlled by the following parameters of a Snapper configuration.


Enables or disables clean-up of timeline snapshots. If enabled, snapshots are deleted when the total snapshot count exceeds a number specified with TIMELINE_LIMIT_* and an age specified with TIMELINE_MIN_AGE. Valid values: yes, no.

The default value is "yes".

Example command to change or set:

snapper -c CONFIG set-config "TIMELINE_CLEANUP=yes"

Number of snapshots to keep for hour, day, month, week, and year.

The default value for each entry is "10", except for TIMELINE_LIMIT_WEEKLY, which is set to "0" by default.


Defines the minimum age in seconds a snapshot must have before it can automatically be deleted.

The default value is "1800".

Example 3.3: Example timeline configuration

This example configuration enables hourly snapshots which are automatically cleaned up. TIMELINE_MIN_AGE and TIMELINE_LIMIT_* are always both evaluated. In this example, the minimum age of a snapshot before it can be deleted is set to 30 minutes (1800 seconds). Since we create hourly snapshots, this ensures that only the latest snapshots are kept. If TIMELINE_LIMIT_DAILY is set to not zero, this means that the first snapshot of the day is kept, too.

Snapshots to be Kept
  • Hourly: The last 24 snapshots that have been made.

  • Daily: The first daily snapshot that has been made is kept from the last seven days.

  • Monthly: The first snapshot made on the last day of the month is kept for the last twelve months.

  • Weekly: The first snapshot made on the last day of the week is kept from the last four weeks.

  • Yearly: The first snapshot made on the last day of the year is kept for the last two years.

3.6.3 Cleaning Up Snapshot Pairs That Do Not Differ

As explained in Section 3.1.1, “Types of Snapshots”, whenever you run a YaST module or execute Zypper, a pre snapshot is created on start-up and a post snapshot is created when exiting. In case you have not made any changes there will be no difference between the pre and post snapshots. Such empty snapshot pairs can be automatically be deleted by setting the following parameters in a Snapper configuration:


If set to yes, pre and post snapshot pairs that do not differ will be deleted.

The default value is "yes".


Defines the minimum age in seconds a pre and post snapshot pair that does not differ must have before it can automatically be deleted.

The default value is "1800".

3.6.4 Cleaning Up Manually Created Snapshots

Snapper does not offer custom clean-up algorithms for manually created snapshots. However, you can assign the number or timeline clean-up algorithm to a manually created snapshot. If you do so, the snapshot will join the clean-up queue for the algorithm you specified. You can specify a clean-up algorithm when creating a snapshot, or by modifying an existing snapshot:

snapper create --description "Test" --cleanup-algorithm number

Creates a stand-alone snapshot (type single) for the default (root) configuration and assigns the number clean-up algorithm.

snapper modify --cleanup-algorithm "timeline" 25

Modifies the snapshot with the number 25 and assigns the clean-up algorithm timeline.

3.6.5 Adding Disk Quota Support

In addition to the number and/or timeline clean-up algorithms described above, Snapper supports quotas. You can define what percentage of the available space snapshots are allowed to occupy. This percentage value always applies to the Btrfs subvolume defined in the respective Snapper configuration.

If Snapper was enabled during the installation, quota support is automatically enabled. In case you manually enable Snapper at a later point in time, you can enable quota support by running snapper setup-quota. This requires a valid configuration (see Section 3.4, “Creating and Modifying Snapper Configurations” for more information).

Quota support is controlled by the following parameters of a Snapper configuration.


The Btrfs quota group used by Snapper. If not set, run snapper setup-quota. If already set, only change if you are familiar with man 8 btrfs-qgroup. This value is set with snapper setup-quota and should not be changed.


Limit of space snapshots are allowed to use in fractions of 1 (100%). Valid values range from 0 to 1 (0.1 = 10%, 0.2 = 20%, ...).

The following limitations and guidelines apply:

  • Quotas are only activated in addition to an existing number and/or timeline clean-up algorithm. If no clean-up algorithm is active, quota restrictions are not applied.

  • With quota support enabled, Snapper will perform two clean-up runs if required. The first run will apply the rules specified for number and timeline snapshots. Only if the quota is exceeded after this run, the quota-specific rules will be applied in a second run.

  • Even if quota support is enabled, Snapper will always keep the number of snapshots specified with the NUMBER_LIMIT* and TIMELINE_LIMIT* values, even if the quota will be exceeded. It is therefore recommended to specify ranged values (min-max) for NUMBER_LIMIT* and TIMELINE_LIMIT* to ensure the quota can be applied.

    If, for example, NUMBER_LIMIT=5-20 is set, Snapper will perform a first clean up run and reduce the number of regular numbered snapshots to 20. In case these 20 snapshots exceed the quota, Snapper will delete the oldest ones in a second run until the quota is met. A minimum of five snapshots will always be kept, regardless of the amount of space they occupy.

3.7 Frequently Asked Questions

Why does Snapper Never Show Changes in /var/log, /tmp and Other Directories?

For some directories we decided to exclude them from snapshots. See Section 3.1.2, “Directories That Are Excluded from Snapshots” for a list and reasons. To exclude a path from snapshots we create a subvolume for that path.

How much disk space is used by snapshots? How to free disk space?

Displaying the amount of disk space a snapshot allocates is currently not supported by the Btrfs tools. However, if you have quota enabled, it is possible to determine how much space would be freed if all snapshots would be deleted:

  1. Get the quota group ID (1/0 in the following example):

    root # snapper -c root get-config | grep QGROUP
    QGROUP                 | 1/0
  2. Rescan the subvolume quotas:

    btrfs quota rescan -w /
  3. Show the data of the quota group (1/0 in the following example):

    root # btrfs qgroup show / | grep "1/0"
    1/0           4.80GiB    108.82MiB

    The third column shows the amount of space that would be freed when deleting all snapshots (108.82MiB).

To free space on a Btrfs partition containing snapshots you need to delete unneeded snapshots rather than files. Older snapshots occupy more space than recent ones. See Section, “Controlling Snapshot Archiving” for details.

Doing an upgrade from one service pack to another results in snapshots occupying a lot of disk space on the system subvolumes, because a lot of data gets changed (package updates). Manually deleting these snapshots after they are no longer needed is recommended. See Section 3.5.4, “Deleting Snapshots” for details.

Can I Boot a Snapshot from the Boot Loader?

Yes—refer to Section 3.3, “System Rollback by Booting from Snapshots” for details.

How to make a snapshot permanent?

Currently Snapper does not offer means to prevent a snapshot from being deleted manually. However, you can prevent snapshots from being automatically deleted by clean-up algorithms. Manually created snapshots (see Section 3.5.2, “Creating Snapshots”) have no clean-up algorithm assigned unless you specify one with --cleanup-algorithm. Automatically created snapshots always either have the number or timeline algorithm assigned. To remove such an assignment from one or more snapshots, proceed as follows:

  1. List all available snapshots:

    snapper list -a
  2. Memorize the number of the snapshot(s) you want to prevent from being deleted.

  3. Run the following command and replace the number placeholders with the number(s) you memorized:

    snapper modify --cleanup-algorithm "" #1 #2 #n
  4. Check the result by running snapper list -a again. The entry in the column Cleanup should now be empty for the snapshots you modified.

Where can I get more information on Snapper?

See the Snapper home page at

4 Remote Access with VNC


Virtual Network Computing (VNC) enables you to control a remote computer via a graphical desktop (as opposed to a remote shell access). VNC is platform-independent and lets you access the remote machine from any operating system.

openSUSE Leap supports two different kinds of VNC sessions: One-time sessions that live as long as the VNC connection from the client is kept up, and persistent sessions that live until they are explicitly terminated.

Note: Session Types

A machine can offer both kinds of sessions simultaneously on different ports, but an open session cannot be converted from one type to the other.

4.1 The vncviewer Client

To connect to a VNC service provided by a server, a client is needed. The default in openSUSE Leap is vncviewer, provided by the tigervnc package.

4.1.1 Connecting Using the vncviewer CLI

To start your VNC viewer and initiate a session with the server, use the command:


Instead of the VNC display number you can also specify the port number with two colons:

Note: Note: Display and Port Number

The actual display or port number you specify in the VNC client must be the same as the display or port number picked by the vncserver command on the target machine. See Section 4.3, “Persistent VNC Sessions” for further info.

4.1.2 Connecting Using the vncviewer GUI

By running vncviewer without specifying --listen or a host to connect to, it will show a window to ask for connection details. Enter the host into the VNC server field like in Section 4.1.1, “Connecting Using the vncviewer CLI” and click Connect.

vncviewer asking for connection details
Figure 4.1: vncviewer

4.1.3 Notification of Unencrypted Connections

The VNC protocol supports different kinds of encrypted connections, not to be confused with password authentication. If a connection does not use TLS, the text (Connection not encrypted!) can be seen in the window title of the VNC viewer.

4.2 One-time VNC Sessions

A one-time session is initiated by the remote client. It starts a graphical login screen on the server. This way you can choose the user which starts the session and, if supported by the login manager, the desktop environment. When you terminate the client connection to such a VNC session, all applications started within that session will be terminated, too. One-time VNC sessions cannot be shared, but it is possible to have multiple sessions on a single host at the same time.

Procedure 4.1: Enabling One-time VNC Sessions
  1. Start YaST › Network Services › Remote Administration (VNC).

  2. Check Allow Remote Administration.

  3. If necessary, also check Open Port in Firewall (for example, when your network interface is configured to be in the External Zone). If you have more than one network interface, restrict opening the firewall ports to a specific interface via Firewall Details.

  4. Confirm your settings with Finish.

  5. In case not all needed packages are available yet, you need to approve the installation of missing packages.

4.2.1 Available Configurations

The default configuration on openSUSE Leap serves sessions with a resolution of 1024x768 pixels at a color depth of 16-bit. The sessions are available on ports 5901 for regular VNC viewers (equivalent to VNC display 1) and on port 5801 for Web browsers.

Other configurations can be made available on different ports, see Section 4.2.3, “Configuring One-time VNC Sessions”.

VNC display numbers and X display numbers are independent in one-time sessions. A VNC display number is manually assigned to every configuration that the server supports (:1 in the example above). Whenever a VNC session is initiated with one of the configurations, it automatically gets a free X display number.

By default, both the VNC client and server try to communicate securely via a self-signed SSL certificate, which is generated after installation. You can either use the default one, or replace it with your own. When using the self-signed certificate, you need to confirm its signature before the first connection—both in the VNC viewer and the Web browser. The Java client is served over HTTPS, using the same certificate as VNC.

4.2.2 Initiating a One-time VNC Session

To connect to a persistent VNC session, a VNC viewer must be installed, see also Section 4.1, “The vncviewer Client”. Alternatively use a Java-capable Web browser to view the VNC session by entering the following URL:

4.2.3 Configuring One-time VNC Sessions

You can skip this section, if you do not need or want to modify the default configuration.

One-time VNC sessions are started via the xinetd daemon. A configuration file is located at /etc/xinetd.d/vnc. By default it offers six configuration blocks: three for VNC viewers (vnc1 to vnc3), and three serving a Java applet (vnchttpd1 to vnchttpd3). By default only vnc1 and vnchttpd1 are active.

To activate a configuration, comment the line disable = yes with a # character in the first column, or remove that line completely. To deactivate a configuration uncomment or add that line.

The Xvnc server can be configured via the server_args option—see Xnvc --help for a list of options.

When adding custom configurations, make sure they are not using ports that are already in use by other configurations, other services, or existing persistent VNC sessions on the same host.

Activate configuration changes by entering the following command:

sudo systemctl reload xinetd
Important: Firewall and VNC Ports

When activating Remote Administration as described in Procedure 4.1, “Enabling One-time VNC Sessions”, the ports 5801 and 5901 are opened in the firewall. If the network interface serving the VNC sessions is protected by a firewall, you need to manually open the respective ports when activating additional ports for VNC sessions. See Book “Security Guide”, Chapter 15 “Masquerading and Firewalls” for instructions.

4.3 Persistent VNC Sessions

A persistent VNC session is initiated on the server. The session and all applications started in this session run regardless of client connections until the session is terminated.

A persistent session can be accessed from multiple clients simultaneously. This is ideal for demonstration purposes where one client has full access and all other clients have view-only access. Another use case are trainings where the trainer might need access to the trainee's desktop. However, most of the times you probably do not want to share your VNC session.

In contrast to one-time sessions that start a display manager, a persistent session starts a ready-to-operate desktop that runs as the user that started the VNC session. Access to persistent sessions is protected by a password.

Access to persistent sessions is protected by two possible types of passwords:

  • a regular password that grants full access or

  • an optional view-only password that grants a non-interactive (view-only) access.

A session can have multiple client connections of both kinds at once.

Procedure 4.2: Starting a Persistent VNC Session
  1. Open a shell and make sure you are logged in as the user that should own the VNC session.

  2. If the network interface serving the VNC sessions is protected by a firewall, you need to manually open the port used by your session in the firewall. If starting multiple sessions you may alternatively open a range of ports. See Book “Security Guide”, Chapter 15 “Masquerading and Firewalls” for details on how to configure the firewall.

    vncserver uses the ports 5901 for display :1, 5902 for display :2, and so on. For persistent sessions, the VNC display and the X display usually have the same number.

  3. To start a session with a resolution of 1024x769 pixel and with a color depth of 16-bit, enter the following command:

    vncserver -geometry 1024x768 -depth 16

    The vncserver command picks an unused display number when none is given and prints its choice. See man 1 vncserver for more options.

When running vncserver for the first time, it asks for a password for full access to the session. If needed, you can also provide a password for view-only access to the session.

The password(s) you are providing here are also used for future sessions started by the same user. They can be changed with the vncpasswd command.

Important: Security Considerations

Make sure to use strong passwords of significant length (eight or more characters). Do not share these passwords.

VNC connections are unencrypted, so people who can sniff the network(s) between the two machines can read the password when it gets transferred at the beginning of a session.

To terminate the session shut down the desktop environment that runs inside the VNC session from the VNC viewer as you would shut it down if it was a regular local X session.

If you prefer to manually terminate a session, open a shell on the VNC server and make sure you are logged in as the user that owns the VNC session you want to terminate. Run the following command to terminate the session that runs on display :1: vncserver -kill :1

4.3.1 Connecting to a Persistent VNC Session

To connect to a persistent VNC session, a VNC viewer must be installed, see also Section 4.1, “The vncviewer Client”. Alternatively use a Java-capable Web browser to view the VNC session by entering the following URL:

4.3.2 Configuring Persistent VNC Sessions

Persistent VNC sessions can be configured by editing $HOME/.vnc/xstartup. By default this shell script starts the same GUI/window manager it was started from. In openSUSE Leap this will either be GNOME or IceWM. If you want to start your session with a window manager of your choice, set the variable WINDOWMANAGER:

WINDOWMANAGER=gnome vncserver -geometry 1024x768
WINDOWMANAGER=icewm vncserver -geometry 1024x768
Note: One Configuration for Each User

Persistent VNC sessions are configured in a single per-user configuration. Multiple sessions started by the same user will all use the same start-up and password files.

5 Advanced Disk Setup

Sophisticated system configurations require specific disk setups. All common partitioning tasks can be done with YaST. To get persistent device naming with block devices, use the block devices below /dev/disk/by-id or /dev/disk/by-uuid. Logical Volume Management (LVM) is a disk partitioning scheme that is designed to be much more flexible than the physical partitioning used in standard setups. Its snapshot functionality enables easy creation of data backups. Redundant Array of Independent Disks (RAID) offers increased data integrity, performance, and fault tolerance. openSUSE Leap also supports multipath I/O , and there is also the option to use iSCSI as a networked disk.

5.1 Using the YaST Partitioner

With the expert partitioner, shown in Figure 5.1, “The YaST Partitioner”, manually modify the partitioning of one or several hard disks. You can add, delete, resize, and edit partitions, or access the soft RAID, and LVM configuration.

Warning: Repartitioning the Running System

Although it is possible to repartition your system while it is running, the risk of making a mistake that causes data loss is very high. Try to avoid repartitioning your installed system and always do a complete backup of your data before attempting to do so.

The YaST Partitioner
Figure 5.1: The YaST Partitioner

All existing or suggested partitions on all connected hard disks are displayed in the list of Available Storage in the YaST Expert Partitioner dialog. Entire hard disks are listed as devices without numbers, such as /dev/sda. Partitions are listed as parts of these devices, such as /dev/sda1. The size, type, encryption status, file system, and mount point of the hard disks and their partitions are also displayed. The mount point describes where the partition appears in the Linux file system tree.

Several functional views are available on the left hand System View. Use these views to gather information about existing storage configurations, or to configure functions like RAID, Volume Management, Crypt Files, or view file systems with additional features, such as Btrfs, NFS, or TMPFS.

If you run the expert dialog during installation, any free hard disk space is also listed and automatically selected. To provide more disk space to openSUSE® Leap, free the needed space starting from the bottom toward the top of the list (starting from the last partition of a hard disk toward the first).

5.1.1 Partition Types

Every hard disk has a partition table with space for four entries. Every entry in the partition table corresponds to a primary partition or an extended partition. Only one extended partition entry is allowed, however.

A primary partition simply consists of a continuous range of cylinders (physical disk areas) assigned to a particular operating system. With primary partitions you would be limited to four partitions per hard disk, because more do not fit in the partition table. This is why extended partitions are used. Extended partitions are also continuous ranges of disk cylinders, but an extended partition may be divided into logical partitions itself. Logical partitions do not require entries in the partition table. In other words, an extended partition is a container for logical partitions.

If you need more than four partitions, create an extended partition as the fourth partition (or earlier). This extended partition should occupy the entire remaining free cylinder range. Then create multiple logical partitions within the extended partition. The maximum number of logical partitions is 63, independent of the disk type. It does not matter which types of partitions are used for Linux. Primary and logical partitions both function normally.

Tip: GPT Partition Table

If you need to create more than 4 primary partitions on one hard disk, you need to use the GPT partition type. This type removes the primary partitions number restriction, and supports partitions bigger than 2 TB as well.

To use GPT, run the YaST Partitioner, click the relevant disk name in the System View and choose Expert › Create New Partition Table › GPT.

5.1.2 Creating a Partition

To create a partition from scratch select Hard Disks and then a hard disk with free space. The actual modification can be done in the Partitions tab:

  1. Select Add and specify the partition type (primary or extended). Create up to four primary partitions or up to three primary partitions and one extended partition. Within the extended partition, create several logical partitions (see Section 5.1.1, “Partition Types”).

  2. Specify the size of the new partition. You can either choose to occupy all the free unpartitioned space, or enter a custom size.

  3. Select the file system to use and a mount point. YaST suggests a mount point for each partition created. To use a different mount method, like mount by label, select Fstab Options. For more information on supported file systems, see root.

  4. Specify additional file system options if your setup requires them. This is necessary, for example, if you need persistent device names. For details on the available options, refer to Section 5.1.3, “Editing a Partition”.

  5. Click Finish to apply your partitioning setup and leave the partitioning module.

    If you created the partition during installation, you are returned to the installation overview screen. Btrfs Partitioning

The default file system for the root partition is Btrfs (see Chapter 3, System Recovery and Snapshot Management with Snapper for more information on Btrfs). The root file system is the default subvolume and it is not listed in the list of created subvolumes. As a default Btrfs subvolume, it can be mounted as a normal file system.

Important: Btrfs on an Encrypted Root Partition

The default partitioning setup suggests the root partition as Btrfs with /boot being a directory. If you need to have the root partition encrypted in this setup, make sure to use the GPT partition table type instead of the default MSDOS type. Otherwise the GRUB2 boot loader may not have enough space for the second stage loader.

It is possible to create snapshots of Btrfs subvolumes—either manually, or automatically based on system events. For example when making changes to the file system, zypper invokes the snapper command to create snapshots before and after the change. This is useful if you are not satisfied with the change zypper made and want to restore the previous state. As snapper invoked by zypper snapshots the root file system by default, it is reasonable to exclude specific directories from being snapshot, depending on the nature of data they hold. And that is why YaST suggests creating the following separate subvolumes.

/boot/grub2/i386-pc, /boot/grub2/x86_64-efi, /boot/grub2/powerpc-ieee1275, /boot/grub2/s390x-emu

A rollback of the boot loader configuration is not supported. The directories listed above are architecture-specific. The first two directories are present on AMD64/Intel 64 machines, the latter two on IBM POWER and on IBM z Systems, respectively.


If /home does not reside on a separate partition, it is excluded to avoid data loss on rollbacks.

/opt, /var/opt

Third-party products usually get installed to /opt. It is excluded to avoid uninstalling these applications on rollbacks.


Contains data for Web and FTP servers. It is excluded to avoid data loss on rollbacks.

/tmp, /var/tmp, /var/cache, /var/crash

All directories containing temporary files and caches are excluded from snapshots.


This directory is used when manually installing software. It is excluded to avoid uninstalling these installations on rollbacks.


The default location for virtual machine images managed with libvirt. Excluded to ensure virtual machine images are not replaced with older versions during a rollback. By default, this subvolume is created with the option no copy on write.

/var/lib/mailman, /var/spool

Directories containing mails or mail queues are excluded to avoid a loss of mails after a rollback.


Contains zone data for the DNS server. Excluded from snapshots to ensure a name server can operate after a rollback.

/var/lib/mariadb, /var/lib/mysql, /var/lib/pgqsl

These directories contain database data. By default, these subvolumes are created with the option no copy on write.


Log file location. Excluded from snapshots to allow log file analysis after the rollback of a broken system.

Tip: Size of Btrfs Partition

Because saved snapshots require more disk space, it is recommended to reserve more space for Btrfs partition than for a partition not capable of snapshotting (such as Ext3). Recommended size for a root Btrfs partition with suggested subvolumes is 20GB. Managing Btrfs Subvolumes using YaST

Subvolumes of a Btrfs partition can be now managed with the YaST Expert partitioner module. You can add new or remove existing subvolumes.

Procedure 5.1: Btrfs Subvolumes with YaST
  1. Start the YaST Expert Partitioner with System › Partitioner.

  2. Choose Btrfs in the left System View pane.

  3. Select the Btrfs partition whose subvolumes you need to manage and click Edit.

  4. Click Subvolume Handling. You can see a list off all existing subvolumes of the selected Btrfs partition. You can notice several @/.snapshots/xyz/snapshot entries—each of these subvolumes belongs to one existing snapshot.

  5. Depending on whether you want to add or remove subvolumes, do the following:

    1. To remove a subvolume, select it from the list of Exisitng Subvolumes and click Remove.

    2. To add a new subvolume, enter its name to the New Subvolume text box and click Add new.

      Btrfs Subvolumes in YaST Partitioner
      Figure 5.2: Btrfs Subvolumes in YaST Partitioner
  6. Confirm with OK and Finish.

  7. Leave the partitioner with Finish.

5.1.3 Editing a Partition

When you create a new partition or modify an existing partition, you can set various parameters. For new partitions, the default parameters set by YaST are usually sufficient and do not require any modification. To edit your partition setup manually, proceed as follows:

  1. Select the partition.

  2. Click Edit to edit the partition and set the parameters:

    File System ID

    Even if you do not want to format the partition at this stage, assign it a file system ID to ensure that the partition is registered correctly. Typical values are Linux, Linux swap, Linux LVM, and Linux RAID.

    File System

    To change the partition file system, click Format Partition and select file system type in the File System list.

    openSUSE Leap supports several types of file systems. Btrfs is the Linux file system of choice for the root partition because of its advanced features. It supports copy-on-write functionality, creating snapshots, multi-device spanning, subvolumes, and other useful techniques. XFS, Ext3 and JFS are journaling file systems. These file systems can restore the system very quickly after a system crash, using write processes logged during the operation. Ext2 is not a journaling file system, but it is adequate for smaller partitions because it does not require much disk space for management.

    The default file system for the root partition is Btrfs. The default file system for additional partitions is XFS.

    Swap is a special format that allows the partition to be used as a virtual memory. Create a swap partition of at least 256 MB. However, if you use up your swap space, consider adding more memory to your system instead of adding more swap space.

    Warning: Changing the File System

    Changing the file system and reformatting partitions irreversibly deletes all data from the partition.

    For details on the various file systems, refer to Storage Administration Guide.

    Encrypt Device

    If you activate the encryption, all data is written to the hard disk in encrypted form. This increases the security of sensitive data, but reduces the system speed, as the encryption takes some time to process. More information about the encryption of file systems is provided in Book “Security Guide”, Chapter 11 “Encrypting Partitions and Files”.

    Mount Point

    Specify the directory where the partition should be mounted in the file system tree. Select from YaST suggestions or enter any other name.

    Fstab Options

    Specify various parameters contained in the global file system administration file (/etc/fstab). The default settings should suffice for most setups. You can, for example, change the file system identification from the device name to a volume label. In the volume label, use all characters except / and space.

    To get persistent devices names, use the mount option Device ID, UUID or LABEL. In openSUSE Leap, persistent device names are enabled by default.

    If you prefer to mount the partition by its label, you need to define one in the Volume label text entry. For example, you could use the partition label HOME for a partition intended to mount to /home.

    If you intend to use quotas on the file system, use the mount option Enable Quota Support. This must be done before you can define quotas for users in the YaST User Management module. For further information on how to configure user quota, refer to Book “Start-Up”, Chapter 3 “Managing Users with YaST”, Section 3.3.4 “Managing Quotas”.

  3. Select Finish to save the changes.

Note: Resize File Systems

To resize an existing file system, select the partition and use Resize. Note, that it is not possible to resize partitions while mounted. To resize partitions, unmount the relevant partition before running the partitioner.

5.1.4 Expert Options

After you select a hard disk device (like sda) in the System View pane, you can access the Expert menu in the lower right part of the Expert Partitioner window. The menu contains the following commands:

Create New Partition Table

This option helps you create a new partition table on the selected device.

Warning: Creating a New Partition Table

Creating a new partition table on a device irreversibly removes all the partitions and their data from that device.

Clone This Disk

This option helps you clone the device partition layout (but not the data) to other available disk devices.

5.1.5 Advanced Options

After you select the host name of the computer (the top-level of the tree in the System View pane), you can access the Configure menu in the lower right part of the Expert Partitioner window. The menu contains the following commands:

Configure iSCSI

To access SCSI over IP block devices, you first need to configure iSCSI. This results in additionally available devices in the main partition list.

Configure Multipath

Selecting this option helps you configure the multipath enhancement to the supported mass storage devices.

5.1.6 More Partitioning Tips

The following section includes a few hints and tips on partitioning that should help you make the right decisions when setting up your system.

Tip: Cylinder Numbers

Note, that different partitioning tools may start counting the cylinders of a partition with 0 or with 1. When calculating the number of cylinders, you should always use the difference between the last and the first cylinder number and add one. Using swap

Swap is used to extend the available physical memory. It is then possible to use more memory than physical RAM available. The memory management system of kernels before 2.4.10 needed swap as a safety measure. Then, if you did not have twice the size of your RAM in swap, the performance of the system suffered. These limitations no longer exist.

Linux uses a page called Least Recently Used (LRU) to select pages that might be moved from memory to disk. Therefore, running applications have more memory available and caching works more smoothly.

If an application tries to allocate the maximum allowed memory, problems with swap can arise. There are three major scenarios to look at:

System with no swap

The application gets the maximum allowed memory. All caches are freed, and thus all other running applications are slowed. After a few minutes, the kernel's out-of-memory kill mechanism activates and kills the process.

System with medium sized swap (128 MB–512 MB)

At first, the system slows like a system without swap. After all physical RAM has been allocated, swap space is used as well. At this point, the system becomes very slow and it becomes impossible to run commands from remote. Depending on the speed of the hard disks that run the swap space, the system stays in this condition for about 10 to 15 minutes until the out-of-memory kill mechanism resolves the issue. Note that you will need a certain amount of swap if the computer needs to perform a suspend to disk. In that case, the swap size should be large enough to contain the necessary data from memory (512 MB–1GB).

System with lots of swap (several GB)

It is better to not have an application that is out of control and swapping excessively in this case. If you use such application, the system will need many hours to recover. In the process, it is likely that other processes get timeouts and faults, leaving the system in an undefined state, even after terminating the faulty process. In this case, do a hard machine reboot and try to get it running again. Lots of swap is only useful if you have an application that relies on this feature. Such applications (like databases or graphics manipulation programs) often have an option to directly use hard disk space for their needs. It is advisable to use this option instead of using lots of swap space.

If your system is not out of control, but needs more swap after some time, it is possible to extend the swap space online. If you prepared a partition for swap space, add this partition with YaST. If you do not have a partition available, you can also use a swap file to extend the swap. Swap files are generally slower than partitions, but compared to physical RAM, both are extremely slow so the actual difference is negligible.

Procedure 5.2: Adding a Swap File Manually

To add a swap file in the running system, proceed as follows:

  1. Create an empty file in your system. For example, if you want to add a swap file with 128 MB swap at /var/lib/swap/swapfile, use the commands:

    mkdir -p /var/lib/swap
    dd if=/dev/zero of=/var/lib/swap/swapfile bs=1M count=128
  2. Initialize this swap file with the command

    mkswap /var/lib/swap/swapfile
    Note: Changed UUID for Swap Partitions when Formatting via mkswap

    Do not reformat existing swap partitions with mkswap if possible. Reformatting with mkswap will change the UUID value of the swap partition. Either reformat via YaST (will update /etc/fstab) or adjust /etc/fstab manually.

  3. Activate the swap with the command

    swapon /var/lib/swap/swapfile

    To disable this swap file, use the command

    swapoff /var/lib/swap/swapfile
  4. Check the current available swap spaces with the command

    cat /proc/swaps

    Note that at this point, it is only temporary swap space. After the next reboot, it is no longer used.

  5. To enable this swap file permanently, add the following line to /etc/fstab:

    /var/lib/swap/swapfile swap swap defaults 0 0

5.1.7 Partitioning and LVM

From the Expert partitioner, access the LVM configuration by clicking the Volume Management item in the System View pane. However, if a working LVM configuration already exists on your system, it is automatically activated upon entering the initial LVM configuration of a session. In this case, all disks containing a partition (belonging to an activated volume group) cannot be repartitioned. The Linux kernel cannot reread the modified partition table of a hard disk when any partition on this disk is in use. If you already have a working LVM configuration on your system, physical repartitioning should not be necessary. Instead, change the configuration of the logical volumes.

At the beginning of the physical volumes (PVs), information about the volume is written to the partition. To reuse such a partition for other non-LVM purposes, it is advisable to delete the beginning of this volume. For example, in the VG system and PV /dev/sda2, do this with the command dd if=/dev/zero of=/dev/sda2 bs=512 count=1.

Warning: File System for Booting

The file system used for booting (the root file system or /boot) must not be stored on an LVM logical volume. Instead, store it on a normal physical partition.

In case you want to change your /usr or swap, refer to Procedure 9.1, “Updating Init RAM Disk When Switching to Logical Volumes”.

5.2 LVM Configuration

This section explains specific steps to take when configuring LVM.

Warning: Back up Your Data

Using LVM is sometimes associated with increased risk such as data loss. Risks also include application crashes, power failures, and faulty commands. Save your data before implementing LVM or reconfiguring volumes. Never work without a backup.

5.2.1 LVM Configuration with YaST

The YaST LVM configuration can be reached from the YaST Expert Partitioner (see Section 5.1, “Using the YaST Partitioner”) within the Volume Management item in the System View pane. The Expert Partitioner allows you to edit and delete existing partitions and create new ones that need to be used with LVM. The first task is to create PVs that provide space to a volume group:

  1. Select a hard disk from Hard Disks.

  2. Change to the Partitions tab.

  3. Click Add and enter the desired size of the PV on this disk.

  4. Use Do not format partition and change the File System ID to 0x8E Linux LVM. Do not mount this partition.

  5. Repeat this procedure until you have defined all the desired physical volumes on the available disks. Creating Volume Groups

If no volume group exists on your system, you must add one (see Figure 5.3, “Creating a Volume Group”). It is possible to create additional groups by clicking Volume Management in the System View pane, and then on Add Volume Group. One single volume group is usually sufficient.

  1. Enter a name for the VG, for example, system.

  2. Select the desired Physical Extend Size. This value defines the size of a physical block in the volume group. All the disk space in a volume group is handled in blocks of this size.

  3. Add the prepared PVs to the VG by selecting the device and clicking Add. Selecting several devices is possible by holding Ctrl while selecting the devices.

  4. Select Finish to make the VG available to further configuration steps.

Creating a Volume Group
Figure 5.3: Creating a Volume Group

If you have multiple volume groups defined and want to add or remove PVs, select the volume group in the Volume Management list and click Resize. In the following window, you can add or remove PVs to the selected volume group. Configuring Logical Volumes

After the volume group has been filled with PVs, define the LVs which the operating system should use in the next dialog. Choose the current volume group and change to the Logical Volumes tab. Add, Edit, Resize, and Delete LVs as needed until all space in the volume group has been occupied. Assign at least one LV to each volume group.

Logical Volume Management
Figure 5.4: Logical Volume Management

Click Add and go through the wizard-like pop-up that opens:

  1. Enter the name of the LV. For a partition that should be mounted to /home, a name like HOME could be used.

  2. Select the type of the LV. It can be either Normal Volume, Thin Pool, or Thin Volume. Note that you need to create a thin pool first, which can store individual thin volumes. The big advantage of thin provisioning is that the total sum of all thin volumes stored in a thin pool can exceed the size of the pool itself.

  3. Select the size and the number of stripes of the LV. If you have only one PV, selecting more than one stripe is not useful.

  4. Choose the file system to use on the LV and the mount point.

By using stripes it is possible to distribute the data stream in the LV among several PVs (striping). However, striping a volume can only be done over different PVs, each providing at least the amount of space of the volume. The maximum number of stripes equals to the number of PVs, where Stripe "1" means "no striping". Striping only makes sense with PVs on different hard disks, otherwise performance will decrease.

Warning: Striping

YaST cannot, at this point, verify the correctness of your entries concerning striping. Any mistake made here is apparent only later when the LVM is implemented on disk.

If you have already configured LVM on your system, the existing logical volumes can also be used. Before continuing, assign appropriate mount points to these LVs. With Finish, return to the YaST Expert Partitioner and finish your work there.

5.3 Soft RAID Configuration with YaST

This section describes actions required to create and configure various types of RAID. .

5.3.1 Soft RAID Configuration with YaST

The YaST RAID configuration can be reached from the YaST Expert Partitioner, described in Section 5.1, “Using the YaST Partitioner”. This partitioning tool enables you to edit and delete existing partitions and create new ones to be used with soft RAID:

  1. Select a hard disk from Hard Disks.

  2. Change to the Partitions tab.

  3. Click Add and enter the desired size of the raid partition on this disk.

  4. Use Do not Format the Partition and change the File System ID to 0xFD Linux RAID. Do not mount this partition.

  5. Repeat this procedure until you have defined all the desired physical volumes on the available disks.

For RAID 0 and RAID 1, at least two partitions are needed—for RAID 1, usually exactly two and no more. If RAID 5 is used, at least three partitions are required, RAID 6 and RAID 10 require at least four partitions. It is recommended to use partitions of the same size only. The RAID partitions should be located on different hard disks to decrease the risk of losing data if one is defective (RAID 1 and 5) and to optimize the performance of RAID 0. After creating all the partitions to use with RAID, click RAID › Add RAID to start the RAID configuration.

In the next dialog, choose between RAID levels 0, 1, 5, 6 and 10. Then, select all partitions with either the Linux RAID or Linux native type that should be used by the RAID system. No swap or DOS partitions are shown.

Tip: Classify Disks

For RAID types where the order of added disks matters, you can mark individual disks with one of the letters A to E. Click the Classify button, select the disk and click of the Class X buttons, where X is the letter you want to assign to the disk. Assign all available RAID disks this way, and confirm with OK. You can easily sort the classified disks with the Sorted or Interleaved buttons, or add a sort pattern from a text file with Pattern File.

RAID Partitions
Figure 5.5: RAID Partitions

To add a previously unassigned partition to the selected RAID volume, first click the partition then Add. Assign all partitions reserved for RAID. Otherwise, the space on the partition remains unused. After assigning all partitions, click Next to select the available RAID Options.

In this last step, set the file system to use, encryption and the mount point for the RAID volume. After completing the configuration with Finish, see the /dev/md0 device and others indicated with RAID in the expert partitioner.

5.3.2 Troubleshooting

Check the file /proc/mdstat to find out whether a RAID partition has been damaged. If Th system fails, shut down your Linux system and replace the defective hard disk with a new one partitioned the same way. Then restart your system and enter the command mdadm /dev/mdX --add /dev/sdX. Replace 'X' with your particular device identifiers. This integrates the hard disk automatically into the RAID system and fully reconstructs it.

Note that although you can access all data during the rebuild, you may encounter some performance issues until the RAID has been fully rebuilt.

5.3.3 For More Information

Configuration instructions and more details for soft RAID can be found in the HOWTOs at:

Linux RAID mailing lists are available, such as

6 Installing Multiple Kernel Versions


openSUSE Leap supports the parallel installation of multiple kernel versions. When installing a second kernel, a boot entry and an initrd are automatically created, so no further manual configuration is needed. When rebooting the machine, the newly added kernel is available as an additional boot option.

Using this functionality, you can safely test kernel updates while being able to always fall back to the proven former kernel. To do so, do not use the update tools (such as the YaST Online Update or the updater applet), but instead follow the process described in this chapter.

Warning: Support Entitlement

Be aware that you lose your entire support entitlement for the machine when installing a self-compiled or a third-party kernel. Only kernels shipped with openSUSE Leap and kernels delivered via the official update channels for openSUSE Leap are supported.

Tip: Check Your Boot Loader Configuration Kernel

It is recommended to check your boot loader configuration after having installed another kernel to set the default boot entry of your choice. See Section 12.3, “Configuring the Boot Loader with YaST” for more information.

6.1 Enabling and Configuring Multiversion Support

Installing multiple versions of a software package (multiversion support) is enabled by default on SUSE Linux Enterprise 12. To verify this setting, proceed as follows:

  1. Open /etc/zypp/zypp.conf with the editor of your choice as root.

  2. Search for the string multiversion. If multiversion is enabled for all kernel packages capable of this feature, the following line appears uncommented:

    multiversion = provides:multiversion(kernel)
  3. To restrict multiversion support to certain kernel flavors, add the package names as a comma-separated list to the multiversion option in /etc/zypp/zypp.conf—for example

    multiversion = kernel-default,kernel-default-base,kernel-source
  4. Save your changes.

Warning: Kernel Module Packages (KMP)

Make sure that required vendor provided kernel modules (Kernel Module Packages) are also installed for the new updated kernel. The kernel update process will not warn about eventually missing kernel modules because package requirements are still fulfilled by the old kernel that is kept on the system.

6.1.1 Automatically Deleting Unused Kernels

When frequently testing new kernels with multiversion support enabled, the boot menu quickly becomes confusing. Since a /boot partition usually has limited space you also might run into trouble with /boot overflowing. While you may delete unused kernel versions manually with YaST or Zypper (as described below), you can also configure libzypp to automatically delete kernels no longer used. By default no kernels are deleted.

  1. Open /etc/zypp/zypp.conf with the editor of your choice as root.

  2. Search for the string multiversion.kernels and activate this option by uncommenting the line. This option takes a comma-separated list of the following values:

    3.12.24-7.1 keep the kernel with the specified version number

    latest keep the kernel with the highest version number

    latest-N keep the kernel with the Nth highest version number

    running keep the running kernel

    oldest keep the kernel with the lowest version number (the one that was originally shipped with openSUSE Leap)

    oldest+N keep the kernel with the Nth lowest version number

    Here are some examples

    multiversion.kernels = latest,running

    Keep the latest kernel and the one currently running. This is similar to not enabling the multiversion feature, except that the old kernel is removed after the next reboot and not immediately after the installation.

    multiversion.kernels = latest,latest-1,running

    Keep the last two kernels and the one currently running.

    multiversion.kernels = latest,running,3.12.25.rc7-test

    Keep the latest kernel, the one currently running, and 3.12.25.rc7-test.

    Tip: Keep the running Kernel

    Unless using special setups, you probably always want to keep the running Kernel. If not keeping the running Kernel, it will be deleted in case of a Kernel update. This in turn makes it necessary to immediately reboot the system after the update, since modules for the Kernel that is currently running can no longer be loaded since they have been deleted.

6.2 Installing/Removing Multiple Kernel Versions with YaST

  1. Start YaST and open the software manager via Software › Software Management.

  2. List all packages capable of providing multiple versions by choosing View › Package Groups › Multiversion Packages.

    The YaST Software Manager: Multiversion View
    Figure 6.1: The YaST Software Manager: Multiversion View
  3. Select a package and open its Version tab in the bottom pane on the left.

  4. To install a package, click its check box. A green check mark indicates it is selected for installation.

    To remove an already installed package (marked with a white check mark), click its check box until a red X indicates it is selected for removal.

  5. Click Accept to start the installation.

6.3 Installing/Removing Multiple Kernel Versions with Zypper

  1. Use the command zypper se -s 'kernel*' to display a list of all kernel packages available:

    S | Name           | Type       | Version         | Arch   | Repository        
    v | kernel-default | package    | | x86_64 | Alternative Kernel
    i | kernel-default | package    |  | x86_64 | (System Packages) 
      | kernel-default | srcpackage | | noarch | Alternative Kernel
    i | kernel-default | package    |  | x86_64 | (System Packages)
  2. Specify the exact version when installing:

    zypper in kernel-default-
  3. When uninstalling a kernel, use the commands zypper se -si 'kernel*' to list all kernels installed and zypper rm PACKAGENAME-VERSION to remove the package.

7 GNOME Configuration for Administrators

This chapter introduces GNOME configuration options which administrators can use to adjust system-wide settings, such as customizing menus, installing themes, configuring fonts, changing preferred applications, and locking down capabilities.

These configuration options are stored in the GConf system. Access the GConf system with tools such as the gconftool-2 command line interface or the gconf-editor GUI tool.

7.1 Starting Applications Automatically

To automatically start applications in GNOME, use one of the following methods:

  • To run applications for each user:  Put .desktop files in /usr/share/gnome/autostart.

  • To run applications for an individual user:  Put .desktop files in ~/.config/autostart.

To disable an application that starts automatically, add X-Autostart-enabled=false to the .desktop file.

7.2 Automounting and Managing Media Devices

GNOME Files (nautilus) monitors volume-related events and responds with a user-specified policy. You can use GNOME Files to automatically mount hotplugged drives and inserted removable media, automatically run programs, and play audio CDs or video DVDs. GNOME Files can also automatically import photos from a digital camera.

System administrators can set system-wide defaults. For more information, see Section 7.3, “Changing Preferred Applications”.

7.3 Changing Preferred Applications

To change users' preferred applications, edit /etc/gnome_defaults.conf. Find further hints within this file.

For more information about MIME types, see

7.4 Adding Document Templates

To add document templates for users, fill in the Templates directory in a user's home directory. You can do this manually for each user by copying the files into ~/Templates, or system-wide by adding a Templates directory with documents to /etc/skel before the user is created.

A user creates a new document from a template by right-clicking the desktop and selecting Create Document.

7.5 For More Information

For more information, see

Part II System

8 32-Bit and 64-Bit Applications in a 64-Bit System Environment

openSUSE® Leap is available for 64-bit platforms. This does not necessarily mean that all the applications included have already been ported to 64-bit platforms. openSUSE Leap supports the use of 32-bit applications in a 64-bit system environment. This chapter offers a brief overview of how this sup…

9 Booting a Linux System

Booting a Linux system involves different components and tasks. The hardware itself is initialized by the BIOS or the UEFI, which starts the Kernel by means of a boot loader. After this point, the boot process is completely controlled by the operating system and handled by systemd. systemd provides a set of targets that boot setups for everyday usage, maintenance or emergencies.

10 The systemd Daemon

The program systemd is the process with process ID 1. It is responsible for initializing the system in the required way. systemd is started directly by the Kernel and resists signal 9, which normally terminates processes. All other programs are either started directly by systemd or by one of its chi…

11 journalctl: Query the systemd Journal

When systemd replaced traditional init scripts in SUSE Linux Enterprise 12 (see Chapter 10, The systemd Daemon), it introduced its own logging system called journal. There is no need to run a syslog based service anymore, as all system events are written in the journal.

12 The Boot Loader GRUB 2

This chapter describes how to configure GRUB 2, the boot loader used in openSUSE® Leap. It is the successor of the traditional GRUB boot loader—now called GRUB Legacy. A YaST module is available for configuring the most important settings. The boot procedure as a whole is outlined in Chapter 9, Booting a Linux System. For details on Secure Boot support for UEFI machines, see Chapter 14, UEFI (Unified Extensible Firmware Interface).

13 Basic Networking

Linux offers the necessary networking tools and features for integration into all types of network structures. Network access using a network card can be configured with YaST. Manual configuration is also possible. In this chapter only the fundamental mechanisms and the relevant network configuration files are covered.

14 UEFI (Unified Extensible Firmware Interface)

UEFI (Unified Extensible Firmware Interface) is the interface between the firmware that comes with the system hardware, all the hardware components of the system, and the operating system.

15 Special System Features

This chapter starts with information about various software packages, the virtual consoles and the keyboard layout. We talk about software components like bash, cron and logrotate, because they were changed or enhanced during the last release cycles. Even if they are small or considered of minor importance, users should change their default behavior, because these components are often closely coupled with the system. The chapter concludes with a section about language and country-specific settings (I18N and L10N).

16 Dynamic Kernel Device Management with udev

The kernel can add or remove almost any device in a running system. Changes in the device state (whether a device is plugged in or removed) need to be propagated to user space. Devices need to be configured as soon as they are plugged in and recognized. Users of a certain device need to be informed …

8 32-Bit and 64-Bit Applications in a 64-Bit System Environment

openSUSE® Leap is available for 64-bit platforms. This does not necessarily mean that all the applications included have already been ported to 64-bit platforms. openSUSE Leap supports the use of 32-bit applications in a 64-bit system environment. This chapter offers a brief overview of how this support is implemented on 64-bit openSUSE Leap platforms. It explains how 32-bit applications are executed (runtime support) and how 32-bit applications should be compiled to enable them to run both in 32-bit and 64-bit system environments. Additionally, find information about the kernel API and an explanation of how 32-bit applications can run under a 64-bit kernel.

openSUSE Leap for the 64-bit platforms amd64 and Intel 64 is designed so that existing 32-bit applications run in the 64-bit environment out-of-the-box. This support means that you can continue to use your preferred 32-bit applications without waiting for a corresponding 64-bit port to become available.

8.1 Runtime Support

Important: Conflicts Between Application Versions

If an application is available both for 32-bit and 64-bit environments, parallel installation of both versions is bound to lead to problems. In such cases, decide on one of the two versions and install and use this.

An exception to this rule is PAM (pluggable authentication modules). openSUSE Leap uses PAM in the authentication process as a layer that mediates between user and application. On a 64-bit operating system that also runs 32-bit applications it is necessary to always install both versions of a PAM module.

To be executed correctly, every application requires a range of libraries. Unfortunately, the names for the 32-bit and 64-bit versions of these libraries are identical. They must be differentiated from each other in another way.

To retain compatibility with the 32-bit version, the libraries are stored at the same place in the system as in the 32-bit environment. The 32-bit version of is located under /lib/ in both the 32-bit and 64-bit environments.

All 64-bit libraries and object files are located in directories called lib64. The 64-bit object files that you would normally expect to find under /lib and /usr/lib are now found under /lib64 and /usr/lib64. This means that there is space for the 32-bit libraries under /lib and /usr/lib, so the file name for both versions can remain unchanged.

Subdirectories of 32-bit /lib directories which contain data content that does not depend on the word size are not moved. This scheme conforms to LSB (Linux Standards Base) and FHS (File System Hierarchy Standard).

8.2 Software Development

All 64-bit architectures support the development of 64-bit objects. The level of support for 32-bit compiling depends on the architecture. These are the various implementation options for the toolchain from GCC (GNU Compiler Collection) and binutils, which include the assembler as and the linker ld:

Both 32-bit and 64-bit objects can be generated with a biarch development toolchain. A biarch development toolchain allows generation of 32-bit and 64-bit objects. The compilation of 64-bit objects is the default on almost all platforms. 32-bit objects can be generated if special flags are used. This special flag is -m32 for GCC. The flags for the binutils are architecture-dependent, but GCC transfers the correct flags to linkers and assemblers. A biarch development toolchain currently exists for amd64 (supports development for x86 and amd64 instructions), for z Systems and for POWER. 32-bit objects are normally created on the POWER platform. The -m64 flag must be used to generate 64-bit objects.

All header files must be written in an architecture-independent form. The installed 32-bit and 64-bit libraries must have an API (application programming interface) that matches the installed header files. The normal openSUSE Leap environment is designed according to this principle. In the case of manually updated libraries, resolve these issues yourself.

8.3 Software Compilation on Biarch Platforms

To develop binaries for the other architecture on a biarch architecture, the respective libraries for the second architecture must additionally be installed. These packages are called rpmname-32bit. You also need the respective headers and libraries from the rpmname-devel packages and the development libraries for the second architecture from rpmname-devel-32bit.

For example, to compile a program that uses libaio on a system whose second architecture is a 32-bit architecture (x86_64), you need the following RPMs:


32-bit runtime package


Headers and libraries for 32-bit development


64-bit runtime package


64-bit development headers and libraries

Most open source programs use an autoconf-based program configuration. To use autoconf for configuring a program for the second architecture, overwrite the normal compiler and linker settings of autoconf by running the configure script with additional environment variables.

The following example refers to an x86_64 system with x86 as the second architecture.

  1. Use the 32-bit compiler:

    CC="gcc -m32"
  2. Instruct the linker to process 32-bit objects (always use gcc as the linker front-end):

    LD="gcc -m32"
  3. Set the assembler to generate 32-bit objects:

    AS="gcc -c -m32"
  4. Specify linker flags, such as the location of 32-bit libraries, for example:

  5. Specify the location for the 32-bit object code libraries:

  6. Specify the location for the 32-bit X libraries:


Not all of these variables are needed for every program. Adapt them to the respective program.

An example configure call to compile a native 32-bit application on x86_64 could appear as follows:

CC="gcc -m32"
./configure --prefix=/usr --libdir=/usr/lib --x-libraries=/usr/lib
make install

8.4 Kernel Specifications

The 64-bit kernels for AMD64/Intel 64 offer both a 64-bit and a 32-bit kernel ABI (application binary interface). The latter is identical with the ABI for the corresponding 32-bit kernel. This means that the 32-bit application can communicate with the 64-bit kernel in the same way as with the 32-bit kernel.

The 32-bit emulation of system calls for a 64-bit kernel does not support all the APIs used by system programs. This depends on the platform. For this reason, few applications, like lspci, must be compiled.

A 64-bit kernel can only load 64-bit kernel modules that have been specially compiled for this kernel. It is not possible to use 32-bit kernel modules.

Tip: Kernel-loadable Modules

Some applications require separate kernel-loadable modules. If you intend to use such a 32-bit application in a 64-bit system environment, contact the provider of this application and SUSE to make sure that the 64-bit version of the kernel-loadable module and the 32-bit compiled version of the kernel API are available for this module.

9 Booting a Linux System


Booting a Linux system involves different components and tasks. The hardware itself is initialized by the BIOS or the UEFI, which starts the Kernel by means of a boot loader. After this point, the boot process is completely controlled by the operating system and handled by systemd. systemd provides a set of targets that boot setups for everyday usage, maintenance or emergencies.

9.1 The Linux Boot Process

The Linux boot process consists of several stages, each represented by a different component. The following list briefly summarizes the boot process and features all the major components involved:

  1. BIOS/UEFI.  After turning on the computer, the BIOS or the UEFI initializes the screen and keyboard, and tests the main memory. Up to this stage, the machine does not access any mass storage media. Subsequently, the information about the current date, time, and the most important peripherals are loaded from the CMOS values. When the first hard disk and its geometry are recognized, the system control passes from the BIOS to the boot loader. If the BIOS supports network booting, it is also possible to configure a boot server that provides the boot loader. On AMD64/Intel 64 systems, PXE boot is needed. Other architectures commonly use the BOOTP protocol to get the boot loader.

  2. Boot Loader.  The first physical 512-byte data sector of the first hard disk is loaded into the main memory and the boot loader that resides at the beginning of this sector takes over. The commands executed by the boot loader determine the remaining part of the boot process. Therefore, the first 512 bytes on the first hard disk are called the Master Boot Record (MBR). The boot loader then passes control to the actual operating system, in this case, the Linux Kernel. More information about GRUB 2, the Linux boot loader, can be found in Chapter 12, The Boot Loader GRUB 2. For a network boot, the BIOS acts as the boot loader. It gets the boot image from the boot server and starts the system. This is completely independent of local hard disks.

    If the root file system fails to mount from within the boot environment, it must be checked and repaired before the boot can continue. The file system checker will be automatically started for Ext3 and Ext4 file systems. The repair process is not automated for XFS and Btrfs file systems and the user will be presented with information describing the options available to repair the file system. Once the file system has been successfully repaired, exiting the boot environment will cause the system to retry mounting the root file system and, if successful, the boot will continue normally.

  3. Kernel and initramfs To pass system control, the boot loader loads both the Kernel and an initial RAM-based file system (initramfs) into memory. The contents of the initramfs can be used by the Kernel directly. initramfs contains a small executable called init that handles the mounting of the real root file system. If special hardware drivers are needed before the mass storage can be accessed, they must be in initramfs. For more information about initramfs, refer to Section 9.2, “initramfs. If the system does not have a local hard disk, the initramfs must provide the root file system for the Kernel. This can be done using a network block device like iSCSI or SAN, but it is also possible to use NFS as the root device.

    Note: The init Process Naming

    Two different programs are commonly named init:

    1. the initramfs process mounting the root file system

    2. the operating system process setting up the system

    In this chapter we will therefore refer to them as init on initramfs and systemd, respectively.

  4. init on initramfs This program performs all actions needed to mount the proper root file system. It provides Kernel functionality for the needed file system and device drivers for mass storage controllers with udev. After the root file system has been found, it is checked for errors and mounted. If this is successful, the initramfs is cleaned and the systemd daemon on the root file system is executed. For more information about init on initramfs, refer to Section 9.3, “Init on initramfs. Find more information about udev in Chapter 16, Dynamic Kernel Device Management with udev.

  5. systemd By starting services and mounting file systems, systemd handles the actual booting of the system. systemd is described in Chapter 10, The systemd Daemon.

9.2 initramfs

initramfs is a small cpio archive that the Kernel can load into a RAM disk. It provides a minimal Linux environment that enables the execution of programs before the actual root file system is mounted. This minimal Linux environment is loaded into memory by BIOS or UEFI routines and does not have specific hardware requirements other than sufficient memory. The initramfs archive must always provide an executable named init that executes the systemd daemon on the root file system for the boot process to proceed.

Before the root file system can be mounted and the operating system can be started, the Kernel needs the corresponding drivers to access the device on which the root file system is located. These drivers may include special drivers for certain kinds of hard disks or even network drivers to access a network file system. The needed modules for the root file system may be loaded by init on initramfs. After the modules are loaded, udev provides the initramfs with the needed devices. Later in the boot process, after changing the root file system, it is necessary to regenerate the devices. This is done by the systemd unit udev.service with the command udevtrigger.

If you need to change hardware (for example, hard disks) in an installed system and this hardware requires different drivers to be in the Kernel at boot time, you must update the initramfs file. This is done by calling dracut -f (the option -f overwrites the existing initramfs file). To add a driver for the new hardware, edit /etc/dracut.conf.d/01-dist.conf and add the following line.


Replace driver1 with the module name of the driver. If you need to add more than one driver, list them space-separated (driver1 driver2).

Important: Updating initramfs or init

The boot loader loads initramfs or init in the same way as the Kernel. It is not necessary to re-install GRUB 2 after updating initramfs or init, because GRUB 2 searches the directory for the right file when booting.

Tip: Changing Kernel Variables

If you change the values of some kernel variables via the sysctl interface by editing related files (/etc/sysctl.conf or /etc/sysctl.d/*.conf), the change will be lost on the next system reboot. Even if you load the values with sysctl --system at runtime, the changes are not saved into the initramfs file. You need to update it by calling dracut -f (the option -f overwrites the existing initramfs file).

9.3 Init on initramfs

The main purpose of init on initramfs is to prepare the mounting of and access to the real root file system. Depending on your system configuration, init on initramfs is responsible for the following tasks.

Loading Kernel Modules

Depending on your hardware configuration, special drivers may be needed to access the hardware components of your computer (the most important component being your hard disk). To access the final root file system, the Kernel needs to load the proper file system drivers.

Providing Block Special Files

For each loaded module, the Kernel generates device events. udev handles these events and generates the required special block files on a RAM file system in /dev. Without those special files, the file system and other devices would not be accessible.

Managing RAID and LVM Setups

If you configured your system to hold the root file system under RAID or LVM, init on initramfs sets up LVM or RAID to enable access to the root file system later.

In case you want to change your /usr or swap partitions directly without the help of YaST, further actions are needed. If you forget these steps, your system will start in emergency mode. To avoid starting in emergency mode, perform the following steps:

Procedure 9.1: Updating Init RAM Disk When Switching to Logical Volumes
  1. Edit the corresponding entry in /etc/fstab and replace your previous partitions with the logical volume.

  2. Execute the following commands:

    root # mount -a
    root # swapon -a
  3. Regenerate your initial RAM disk (initramfs) with mkinitrd or dracut.

  4. For z Systems, additionally run grub2-install.

Find more information about RAID and LVM in Chapter 5, Advanced Disk Setup.

Managing Network Configuration

If you configured your system to use a network-mounted root file system (mounted via NFS), init on initramfs must make sure that the proper network drivers are loaded and that they are set up to allow access to the root file system.

If the file system resides on a network block device like iSCSI or SAN, the connection to the storage server is also set up by init on initramfs. openSUSE Leap supports booting from a secondary iSCSI target if the primary target is not available. .

When init on initramfs is called during the initial boot as part of the installation process, its tasks differ from those mentioned above:

Finding the Installation Medium

When starting the installation process, your machine loads an installation Kernel and a special init containing the YaST installer. The YaST installer is running in a RAM file system and needs to have information about the location of the installation medium to access it for installing the operating system.

Initiating Hardware Recognition and Loading Appropriate Kernel Modules

As mentioned in Section 9.2, “initramfs, the boot process starts with a minimum set of drivers that can be used with most hardware configurations. init starts an initial hardware scanning process that determines the set of drivers suitable for your hardware configuration. These drivers are used to generate a custom initramfs that is needed to boot the system. If the modules are not needed for boot but for coldplug, the modules can be loaded with systemd; for more information, see Section 10.6.4, “Loading Kernel Modules”.

Loading the Installation System

When the hardware is properly recognized, the appropriate drivers are loaded. The udev program creates the special device files and init starts the installation system with the YaST installer.

Starting YaST

Finally, init starts YaST, which starts package installation and system configuration.

10 The systemd Daemon

The program systemd is the process with process ID 1. It is responsible for initializing the system in the required way. systemd is started directly by the Kernel and resists signal 9, which normally terminates processes. All other programs are either started directly by systemd or by one of its child processes.

Starting with openSUSE Leap 12 systemd is a replacement for the popular System V init daemon. systemd is fully compatible with System V init (by supporting init scripts). One of the main advantages of systemd is that it considerably speeds up boot time by aggressively paralleling service starts. Furthermore, systemd only starts a service when it is really needed. Daemons are not started unconditionally at boot time, but rather when being required for the first time. systemd also supports Kernel Control Groups (cgroups), snapshotting and restoring the system state and more. See for details.

10.1 The systemd Concept

This section will go into detail about the concept behind systemd.

10.1.1 What Is systemd

systemd is a system and session manager for Linux, compatible with System V and LSB init scripts. The main features are:

  • provides aggressive parallelization capabilities

  • uses socket and D-Bus activation for starting services

  • offers on-demand starting of daemons

  • keeps track of processes using Linux cgroups

  • supports snapshotting and restoring of the system state

  • maintains mount and automount points

  • implements an elaborate transactional dependency-based service control logic

10.1.2 Unit File

A unit configuration file encodes information about a service, a socket, a device, a mount point, an automount point, a swap file or partition, a start-up target, a watched file system path, a timer controlled and supervised by systemd, a temporary system state snapshot, a resource management slice or a group of externally created processes. Unit file is a generic term used by systemd for the following:

  • Service.  Information about a process (for example running a daemon); file ends with .service

  • Targets.  Used for grouping units and as synchronization points during start-up; file ends with .target

  • Sockets.  Information about an IPC or network socket or a file system FIFO, for socket-based activation (like inetd); file ends with .socket

  • Path.  Used to trigger other units (for example running a service when files change); file ends with .path

  • Timer.  Information about a timer controlled, for timer-based activation; file ends with .timer

  • Mount point.  Usually auto-generated by the fstab generator; file ends with .mount

  • Automount point.  Information about a file system automount point; file ends with .automount

  • Swap.  Information about a swap device or file for memory paging; file ends with .swap

  • Device.  Information about a device unit as exposed in the sysfs/udev(7) device tree; file ends with .device

  • Scope / Slice.  A concept for hierarchically managing resources of a group of processes; file ends with .scope/.slice

For more information about systemd.unit see

10.2 Basic Usage

The System V init system uses several commands to handle services—the init scripts, insserv, telinit and others. systemd makes it easier to manage services, since there is only one command to memorize for the majority of service-handling tasks: systemctl. It uses the command plus subcommand notation like git or zypper:

systemctl [general OPTIONS] subcommand [subcommand OPTIONS]

See man 1 systemctl for a complete manual.

Tip: Terminal Output and Bash Completion

If the output goes to a terminal (and not to a pipe or a file, for example) systemd commands send long output to a pager by default. Use the --no-pager option to turn off paging mode.

systemd also supports bash-completion, allowing you to enter the first letters of a subcommand and then press →| to automatically complete it. This feature is only available in the bash shell and requires the installation of the package bash-completion.

10.2.1 Managing Services in a Running System

Subcommands for managing services are the same as for managing a service with System V init (start, stop, ...). The general syntax for service management commands is as follows:

systemctl reload|restart|start|status|stop|... <my_service(s)>
System V init
rc<my_service(s)> reload|restart|start|status|stop|...

systemd allows you to manage several services in one go. Instead of executing init scripts one after the other as with System V init, execute a command like the following:

systemctl start <my_1st_service> <my_2nd_service>

If you want to list all services available on the system:

systemctl list-unit-files --type=service

The following table lists the most important service management commands for systemd and System V init:

Table 10.1: Service Management Commands


systemd Command

System V init Command





Restarting.  Shuts down services and starts them afterward. If a service is not yet running it will be started.


Restarting conditionally.  Restarts services if they are currently running. Does nothing for services that are not running.


Reloading.  Tells services to reload their configuration files without interrupting operation. Use case: Tell Apache to reload a modified httpd.conf configuration file. Note that not all services support reloading.


Reloading or restarting.  Reloads services if reloading is supported, otherwise restarts them. If a service is not yet running it will be started.


Reloading or restarting conditionally.  Reloads services if reloading is supported, otherwise restarts them if currently running. Does nothing for services that are not running.


Getting detailed status information.  Lists information about the status of services. The systemd command shows details such as description, executable, status, cgroup, and messages last issued by a service (see Section 10.6.8, “Debugging Services”). The level of details displayed with the System V init differs from service to service.


Getting short status information.  Shows whether services are active or not.


10.2.2 Permanently Enabling/Disabling Services

The service management commands mentioned in the previous section let you manipulate services for the current session. systemd also lets you permanently enable or disable services, so they are automatically started when requested or are always unavailable. You can either do this by using YaST, or on the command line. Enabling/Disabling Services on the Command Line

The following table lists enabling and disabling commands for systemd and System V init:

Important: Service Start

When enabling a service on the command line, it is not started automatically. It is scheduled to be started with the next system start-up or runlevel/target change. To immediately start a service after having enabled it, explicitly run systemctl start <my_service> or rc <my_service> start.

Table 10.2: Commands for Enabling and Disabling Services


systemd Command

System V init Command


systemctl enable <my_service(s)>

insserv <my_service(s)>


systemctl disable <my_service(s)>.service

insserv -r <my_service(s)>

Checking.  Shows whether a service is enabled or not.

systemctl is-enabled <my_service>


Re-enabling.  Similar to restarting a service, this command first disables and then enables a service. Useful to re-enable a service with its defaults.

systemctl reenable <my_service>


Masking.  After disabling a service, it can still be started manually. To completely disable a service, you need to mask it. Use with care.

systemctl mask <my_service>


Unmasking.  A service that has been masked can only be used again after it has been unmasked.

systemctl unmask <my_service>


10.3 System Start and Target Management

The entire process of starting the system and shutting it down is maintained by systemd. From this point of view, the Kernel can be considered a background process to maintain all other processes and adjust CPU time and hardware access according to requests from other programs.

10.3.1 Targets Compared to Runlevels

With System V init the system was booted into a so-called Runlevel. A runlevel defines how the system is started and what services are available in the running system. Runlevels are numbered; the most commonly known ones are 0 (shutting down the system), 3 (multiuser with network) and 5 (multiuser with network and display manager).

systemd introduces a new concept by using so-called target units. However, it remains fully compatible with the runlevel concept. Target units are named rather than numbered and serve specific purposes. For example, the targets and mount local file systems and swap spaces.

The target provides a multiuser system with network and display manager capabilities and is equivalent to runlevel 5. Complex targets, such as act as meta targets by combining a subset of other targets. Since systemd makes it easy to create custom targets by combining existing targets, it offers great flexibility.

The following list shows the most important systemd target units. For a full list refer to man 7 systemd.special.

Selected systemd Target Units

The target that is booted by default. Not a real target, but rather a symbolic link to another target like Can be permanently changed via YaST (see Section 10.4, “Managing Services with YaST”). To change it for a session, use the Kernel command line option systemd.unit=<my_target>.target at the boot prompt.

Starts an emergency shell on the console. Only use it at the boot prompt as

Starts a system with network, multiuser support and a display manager.

Shuts down the system.

Starts all services necessary for sending and receiving mails.

Starts a multiuser system with network.

Reboots the system.

Starts a single-user system without network.

To remain compatible with the System V init runlevel system, systemd provides special targets named mapping the corresponding runlevels numbered X.

If you want to know the current target, use the command: systemctl get-default

Table 10.3: System V Runlevels and systemd Target Units

System V runlevel

systemd target



System shutdown

1, S,,

Single-user mode


Local multiuser without remote network


Full multiuser with network




Full multiuser with network and display manager


System reboot

Important: systemd Ignores /etc/inittab

The runlevels in a System V init system are configured in /etc/inittab. systemd does not use this configuration. Refer to Section 10.5.3, “Creating Custom Targets” for instructions on how to create your own bootable target. Commands to Change Targets

Use the following commands to operate with target units:


systemd Command

System V init Command

Change the current target/runlevel

systemctl isolate <my_target>.target

telinit X

Change to the default target/runlevel

systemctl default


Get the current target/runlevel

systemctl list-units --type=target

With systemd there is usually more than one active target. The command lists all currently active targets.

who -r



persistently change the default runlevel

Use the Services Manager or run the following command:

ln -sf /usr/lib/systemd/system/ <my_target>.target /etc/systemd/system/

Use the Services Manager or change the line

id: X:initdefault:

in /etc/inittab

Change the default runlevel for the current boot process

Enter the following option at the boot prompt

systemd.unit= <my_target>.target

Enter the desired runlevel number at the boot prompt.

Show a target's/runlevel's dependencies

systemctl show -p "Requires" <my_target>.target

systemctl show -p "Wants" <my_target>.target

Requires lists the hard dependencies (the ones that must be resolved), whereas Wants lists the soft dependencies (the ones that get resolved if possible).


10.3.2 Debugging System Start-Up

systemd offers the means to analyze the system start-up process. You can conveniently review the list of all services and their status (rather than having to parse /varlog/). systemd also allows you to scan the start-up procedure to find out how much time each service start-up consumes. Review Start-Up of Services

To review the complete list of services that have been started since booting the system, enter the command systemctl. It lists all active services like shown below (shortened). To get more information on a specific service, use systemctl status <my_service>.

Example 10.1: List Active Services
root # systemctl
UNIT                        LOAD   ACTIVE SUB       JOB DESCRIPTION
iscsi.service               loaded active exited    Login and scanning of iSC+
kmod-static-nodes.service   loaded active exited    Create list of required s+
libvirtd.service            loaded active running   Virtualization daemon
nscd.service                loaded active running   Name Service Cache Daemon
ntpd.service                loaded active running   NTP Server Daemon
polkit.service              loaded active running   Authorization Manager
postfix.service             loaded active running   Postfix Mail Transport Ag+
rc-local.service            loaded active exited    /etc/init.d/boot.local Co+
rsyslog.service             loaded active running   System Logging Service
LOAD   = Reflects whether the unit definition was properly loaded.
ACTIVE = The high-level unit activation state, i.e. generalization of SUB.
SUB    = The low-level unit activation state, values depend on unit type.

161 loaded units listed. Pass --all to see loaded but inactive units, too.
To show all installed unit files use 'systemctl list-unit-files'.

To restrict the output to services that failed to start, use the --failed option:

Example 10.2: List Failed Services
root # systemctl --failed
apache2.service        loaded failed failed     apache
NetworkManager.service loaded failed failed     Network Manager
plymouth-start.service loaded failed failed     Show Plymouth Boot Screen

[...] Debug Start-Up Time

To debug system start-up time, systemd offers the systemd-analyze command. It shows the total start-up time, a list of services ordered by start-up time and can also generate an SVG graphic showing the time services took to start in relation to the other services.

Listing the System Start-Up Time
root # systemd-analyze
Startup finished in 2666ms (kernel) + 21961ms (userspace) = 24628ms
Listing the Services Start-Up Time
root # systemd-analyze blame
  6472ms systemd-modules-load.service
  5833ms remount-rootfs.service
  4597ms network.service
  4254ms systemd-vconsole-setup.service
  4096ms postfix.service
  2998ms xdm.service
  2483ms localnet.service
  2470ms SuSEfirewall2_init.service
  2189ms avahi-daemon.service
  2120ms systemd-logind.service
  1210ms xinetd.service
  1080ms ntp.service
    75ms fbset.service
    72ms purge-kernels.service
    47ms dev-vda1.swap
    38ms bluez-coldplug.service
    35ms splash_early.service
Services Start-Up Time Graphics
root # systemd-analyze plot > Review the Complete Start-Up Process

The above-mentioned commands let you review the services that started and the time it took to start them. If you need to know more details, you can tell systemd to verbosely log the complete start-up procedure by entering the following parameters at the boot prompt:

systemd.log_level=debug systemd.log_target=kmsg

Now systemd writes its log messages into the kernel ring buffer. View that buffer with dmesg:

dmesg -T | less

10.3.3 System V Compatibility

systemd is compatible with System V, allowing you to still use existing System V init scripts. However, there is at least one known issue where a System V init script does not work with systemd out of the box: starting a service as a different user via su or sudo in init scripts will result in a failure of the script, producing an Access denied error.

When changing the user with su or sudo, a PAM session is started. This session will be terminated after the init script is finished. As a consequence, the service that has been started by the init script will also be terminated. To work around this error, proceed as follows:

  1. Create a service file wrapper with the same name as the init script plus the file name extension .service:

    ExecStart=PATH TO INIT SCRIPT start
    ExecStop=PATH TO INIT SCRIPT stop
    ExecStopPost=/usr/bin/rm -f PATH TO PID FILE1

    Replace all values written in UPPERCASE LETTERS with appropriate values.


    Optional—only use if the init script starts a daemon.

    2 also starts the init script when booting into If it should only be started when booting into the display manager, user here.

  2. Start the daemon with systemctl start APPLICATION.

10.4 Managing Services with YaST

Basic service management can also be done with the YaST Services Manager module. It supports starting, stopping, enabling and disabling services. It also lets you show a service's status and change the default target. Start the YaST module with YaST › System › Services Manager.

Services Manager
Figure 10.1: Services Manager
Changing the Default System Target

To change the target the system boots into, choose a target from the Default System Target drop-down box. The most often used targets are Graphical Interface (starting a graphical login screen) and Multi-User (starting the system in command line mode).

Starting or Stopping a Service

Select a service from the table. The Active column shows whether it is currently running (Active) or not (Inactive). Toggle its status by choosing Start/Stop.

Starting or stopping a service changes its status for the currently running session. To change its status throughout a reboot, you need to enable or disable it.

Enabling or Disabling a Service

Select a service from the table. The Enabled column shows whether it is currently Enabled or Disabled. Toggle its status by choosing Enable/Disable.

By enabling or disabling a service you configure whether it is started during booting (Enabled) or not (Disabled). This setting will not affect the current session. To change its status in the current session, you need to start or stop it.

View a Status Messages

To view the status message of a service, select it from the list and choose Show Details. The output you will see is identical to the one generated by the command systemctl -l status <my_service>.

Warning: Faulty Runlevel Settings May Damage Your System

Faulty runlevel settings may make your system unusable. Before applying your changes, make absolutely sure that you know their consequences.

10.5 Customization of systemd

The following sections contain some examples for systemd customization.

Warning: Avoiding Overwritten Customization

Always do systemd customization in /etc/systemd/, never in /usr/lib/systemd/. Otherwise your changes will be overwritten by the next update of systemd.

10.5.1 Customizing Service Files

The systemd service files are located in /usr/lib/systemd/system. If you want to customize them, proceed as follows:

  1. Copy the files you want to modify from /usr/lib/systemd/system to /etc/systemd/system. Keep the file names identical to the original ones.

  2. Modify the copies in /etc/systemd/system according to your needs.

  3. For an overview of your configuration changes, use the systemd-delta command. It can compare and identify configuration files that override other configuration files. For details, refer to the systemd-delta man page.

The modified files in /etc/systemd will take precedence over the original files in /usr/lib/systemd/system, provided that their file name is the same.

10.5.2 Creating Drop-in Files

If you only want to add a few lines to a configuration file or modify a small part of it, you can use so-called drop-in files. Drop-in files let you extend the configuration of unit files without having to edit or override the unit files themselves.

For example, to change one value for the foobar service located in /usr/lib/systemd/system/foobar.service, proceed as follows:

  1. Create a directory called /etc/systemd/system/<my_service>.service.d/.

    Note the .d suffix. The directory must otherwise be named like the service that you want to patch with the drop-in file.

  2. In that directory, create a file whatevermodification.conf.

    Make sure it only contains the line with the value that you want to modify.

  3. Save your changes to the file. It will be used as an extension of the original file.

10.5.3 Creating Custom Targets

On System V init SUSE systems, runlevel 4 is unused to allow administrators to create their own runlevel configuration. systemd allows you to create any number of custom targets. It is suggested to start by adapting an existing target such as

  1. Copy the configuration file /usr/lib/systemd/system/ to /etc/systemd/system/<my_target>.target and adjust it according to your needs.

  2. The configuration file copied in the previous step already covers the required (hard) dependencies for the target. To also cover the wanted (soft) dependencies, create a directory /etc/systemd/system/<my_target>.target.wants.

  3. For each wanted service, create a symbolic link from /usr/lib/systemd/system into /etc/systemd/system/<my_target>.target.wants.

  4. Once you have finished setting up the target, reload the systemd configuration to make the new target available:

    systemctl daemon-reload

10.6 Advanced Usage

The following sections cover advanced topics for system administrators. For even more advanced systemd documentation, refer to Lennart Pöttering's series about systemd for administrators at

10.6.1 Cleaning Temporary Directories

systemd supports cleaning temporary directories regularly. The configuration from the previous system version is automatically migrated and active. tmpfiles.d—which is responsible for managing temporary files—reads its configuration from /etc/tmpfiles.d/*.conf , /run/tmpfiles.d/*.conf, and /usr/lib/tmpfiles.d/*.conf files. Configuration placed in /etc/tmpfiles.d/*.conf overrides related configurations from the other two directories (/usr/lib/tmpfiles.d/*.conf is where packages store their configuration files).

The configuration format is one line per path containing action and path, and optionally mode, ownership, age and argument fields, depending on the action. The following example unlinks the X11 lock files:

Type Path               Mode UID  GID  Age Argument
r    /tmp/.X[0-9]*-lock

To get the status the tmpfile timer:

systemctl status systemd-tmpfiles-clean.timer
systemd-tmpfiles-clean.timer - Daily Cleanup of Temporary Directories
 Loaded: loaded (/usr/lib/systemd/system/systemd-tmpfiles-clean.timer; static)
 Active: active (waiting) since Tue 2014-09-09 15:30:36 CEST; 1 weeks 6 days ago
   Docs: man:tmpfiles.d(5)

Sep 09 15:30:36 jupiter systemd[1]: Starting Daily Cleanup of Temporary Directories.
Sep 09 15:30:36 jupiter systemd[1]: Started Daily Cleanup of Temporary Directories.

For more information on temporary files handling, see man 5 tmpfiles.d.

10.6.2 System Log

Section 10.6.8, “Debugging Services” explains how to view log messages for a given service. However, displaying log messages is not restricted to service logs. You can also access and query the complete log messages written by systemd—the so-called Journal. Use the command systemd-journalctl to display the complete log messages starting with the oldest entries. Refer to man 1 systemd-journalctl for options such as applying filters or changing the output format.

10.6.3 Snapshots

You can save the current state of systemd to a named snapshot and later revert to it with the isolate subcommand. This is useful when testing services or custom targets, because it allows you to return to a defined state at any time. A snapshot is only available in the current session and will automatically be deleted on reboot. A snapshot name must end in .snapshot.

Create a Snapshot
systemctl snapshot <my_snapshot>.snapshot
Delete a Snapshot
systemctl delete <my_snapshot>.snapshot
View a Snapshot
systemctl show <my_snapshot>.snapshot
Activate a Snapshot
systemctl isolate <my_snapshot>.snapshot

10.6.4 Loading Kernel Modules

With systemd, kernel modules can automatically be loaded at boot time via a configuration file in /etc/modules-load.d. The file should be named module.conf and have the following content:

# load module module at boot time

In case a package installs a configuration file for loading a Kernel module, the file gets installed to /usr/lib/modules-load.d. If two configuration files with the same name exist, the one in /etc/modules-load.d tales precedence.

For more information, see the modules-load.d(5) man page.

10.6.5 Performing Actions Before Loading a Service

With System V init actions that need to be performed before loading a service, needed to be specified in /etc/init.d/before.local . This procedure is no longer supported with systemd. If you need to do actions before starting services, do the following:

Loading Kernel Modules

Create a drop-in file in /etc/modules-load.d directory (see man modules-load.d for the syntax)

Creating Files or Directories, Cleaning-up Directories, Changing Ownership

Create a drop-in file in /etc/tmpfiles.d (see man tmpfiles.d for the syntax)

Other Tasks

Create a system service file, for example /etc/systemd/system/before.service, from the following template:

# beware, executable is run directly, not through a shell, check the man pages
# systemd.service and systemd.unit for full syntax
# target in which to start the service

When the service file is created, you should run the following commands (as root):

systemctl daemon-reload
systemctl enable before

Every time you modify the service file, you need to run:

systemctl daemon-reload

10.6.6 Kernel Control Groups (cgroups)

On a traditional System V init system it is not always possible to clearly assign a process to the service that spawned it. Some services, such as Apache, spawn a lot of third-party processes (for example CGI or Java processes), which themselves spawn more processes. This makes a clear assignment difficult or even impossible. Additionally, a service may not terminate correctly, leaving some children alive.

systemd solves this problem by placing each service into its own cgroup. cgroups are a Kernel feature that allows aggregating processes and all their children into hierarchical organized groups. systemd names each cgroup after its service. Since a non-privileged process is not allowed to leave its cgroup, this provides an effective way to label all processes spawned by a service with the name of the service.

To list all processes belonging to a service, use the command systemd-cgls. The result will look like the following (shortened) example:

Example 10.3: List all Processes Belonging to a Service
root # systemd-cgls --no-pager
├─1 /usr/lib/systemd/systemd --switched-root --system --deserialize 20
│ └─user-1000.slice
│   ├─session-102.scope
│   │ ├─12426 gdm-session-worker [pam/gdm-password]
│   │ ├─15831 gdm-session-worker [pam/gdm-password]
│   │ ├─15839 gdm-session-worker [pam/gdm-password]
│   │ ├─15858 /usr/lib/gnome-terminal-server


  │ └─17616 /usr/lib/systemd/systemd-hostnamed
  │ └─1689 /usr/sbin/cron -n
  │ └─1328 /usr/sbin/ntpd -p /var/run/ntp/ -g -u ntp:ntp -c /etc/ntp.conf
  │ ├─ 1676 /usr/lib/postfix/master -w
  │ ├─ 1679 qmgr -l -t fifo -u
  │ └─15590 pickup -l -t fifo -u
  │ └─1436 /usr/sbin/sshd -D


See Book “System Analysis and Tuning Guide”, Chapter 9 “Kernel Control Groups” for more information about cgroups.

10.6.7 Terminating Services (Sending Signals)

As explained in Section 10.6.6, “Kernel Control Groups (cgroups)”, it is not always possible to assign a process to its parent service process in a System V init system. This makes it difficult to terminate a service and all of its children. Child processes that have not been terminated will remain as zombie processes.

systemd's concept of confining each service into a cgroup makes it possible to clearly identify all child processes of a service and therefore allows you to send a signal to each of these processes. Use systemctl kill to send signals to services. For a list of available signals refer to man 7 signals.

Sending SIGTERM to a Service

SIGTERM is the default signal that is sent.

systemctl kill <my_service>
Sending SIGNAL to a Service

Use the -s option to specify the signal that should be sent.

systemctl kill -s SIGNAL <my_service>
Selecting Processes

By default the kill command sends the signal to all processes of the specified cgroup. You can restrict it to the control or the main process. The latter is for example useful to force a service to reload its configuration by sending SIGHUP:

systemctl kill -s SIGHUP --kill-who=main <my_service>

10.6.8 Debugging Services

By default, systemd is not overly verbose. If a service was started successfully, no output will be produced. In case of a failure, a short error message will be displayed. However, systemctl status provides means to debug start-up and operation of a service.

systemd comes with its own logging mechanism (The Journal) that logs system messages. This allows you to display the service messages together with status messages. The status command works similar to tail and can also display the log messages in different formats, making it a powerful debugging tool.

Show Service Start-Up Failure

Whenever a service fails to start, use systemctl status <my_service> to get a detailed error message:

root # systemctl start apache2
Job failed. See system journal and 'systemctl status' for details.
root # systemctl status apache2
   Loaded: loaded (/usr/lib/systemd/system/apache2.service; disabled)
   Active: failed (Result: exit-code) since Mon, 04 Jun 2012 16:52:26 +0200; 29s ago
   Process: 3088 ExecStart=/usr/sbin/start_apache2 -D SYSTEMD -k start (code=exited, status=1/FAILURE)
   CGroup: name=systemd:/system/apache2.service

Jun 04 16:52:26 g144 start_apache2[3088]: httpd2-prefork: Syntax error on line
205 of /etc/apache2/httpd.conf: Syntax error on li...alHost>
Show Last n Service Messages

The default behavior of the status subcommand is to display the last ten messages a service issued. To change the number of messages to show, use the --lines=n parameter:

systemctl status ntp
systemctl --lines=20 status ntp
Show Service Messages in Append Mode

To display a live stream of service messages, use the --follow option, which works like tail -f:

systemctl --follow status ntp
Messages Output Format

The --output=mode parameter allows you to change the output format of service messages. The most important modes available are:


The default format. Shows the log messages with a human readable time stamp.


Full output with all fields.


Terse output without time stamps.

10.7 More Information

For more information on systemd refer to the following online resources:


systemd for Administrators

Lennart Pöttering, one of the systemd authors, has written a series of blog entries (13 at the time of writing this chapter). Find them at

11 journalctl: Query the systemd Journal

When systemd replaced traditional init scripts in SUSE Linux Enterprise 12 (see Chapter 10, The systemd Daemon), it introduced its own logging system called journal. There is no need to run a syslog based service anymore, as all system events are written in the journal.

The journal itself is a system service managed by systemd. Its full name is systemd-journald.service. It collects and stores logging data by maintaining structured indexed journals based on logging information received from the kernel, from user processes, from standard input and from system service errors. The systemd-journald service is on by default:

# systemctl status systemd-journald
systemd-journald.service - Journal Service
   Loaded: loaded (/usr/lib/systemd/system/systemd-journald.service; static)
   Active: active (running) since Mon 2014-05-26 08:36:59 EDT; 3 days ago
     Docs: man:systemd-journald.service(8)
 Main PID: 413 (systemd-journal)
   Status: "Processing requests..."
   CGroup: /system.slice/systemd-journald.service
           └─413 /usr/lib/systemd/systemd-journald

11.1 Making the Journal Persistent

The journal stores log data in /run/log/journal/ by default. Because the /run/ directory is volatile by nature, log data is lost at reboot. To make the log data persistent, the directory /var/log/journal/ with correct ownership and permissions must exist, where the systemd-journald service can store its data. systemd will create the directory for you—and switch to persistent logging—if you do the following:

  1. As root, open /etc/systemd/journald.conf for editing.

    # vi /etc/systemd/journald.conf
  2. Uncomment the line containing Storage= and change it to

  3. Save the file and restart systemd-journald:

    systemctl restart systemd-journald

11.2 journalctl Useful Switches

This section introduces several common useful options to enhance the default journalctl behavior. All switches are described in the journalctl manual page, man 1 journalctl.

Tip: Messages Related to a Specific Executable

To show all journal messages related to a specific executable, specify the full path to the executable:

journalctl /usr/lib/systemd/systemd

Shows only the most recent journal messages, and prints new log entries as they are added to the journal.


Prints the messages and jumps to the end of the journal, so that the latest entries are visible within the pager.


Prints the messages of the journal in reverse order, so that the latest entries are listed first.


Shows only kernel messages. This is equivalent to the field match _TRANSPORT=kernel (see Section 11.3.3, “Filtering Based on Fields”).


Shows only messages for the specified systemd unit. This is equivalent to the field match _SYSTEMD_UNIT=UNIT (see Section 11.3.3, “Filtering Based on Fields”).

# journalctl -u apache2
Jun 03 10:07:11 pinkiepie systemd[1]: Starting The Apache Webserver...
Jun 03 10:07:12 pinkiepie systemd[1]: Started The Apache Webserver.

11.3 Filtering the Journal Output

When called without switches, journalctl shows the full content of the journal, the oldest entries listed first. The output can be filtered by specific switches and fields.

11.3.1 Filtering Based on a Boot Number

journalctl can filter messages based on a specific system boot. To list all available boots, run

# journalctl --list-boots
-1 097ed2cd99124a2391d2cffab1b566f0 Mon 2014-05-26 08:36:56 EDT—Fri 2014-05-30 05:33:44 EDT
 0 156019a44a774a0bb0148a92df4af81b Fri 2014-05-30 05:34:09 EDT—Fri 2014-05-30 06:15:01 EDT

The first column lists the boot offset: 0 for the current boot, -1 for the previous, -2 for the prior to that, etc. The second column contains the boot ID, and then the limiting time stamps of the specific boot follow.

Show all messages from the current boot:

# journalctl -b

If you need to see journal messages from the previous boot, add an offset parameter. The following example outputs the previous boot messages:

# journalctl -b -1

Another way is to list boot messages based on the boot ID. For this purpose, use the _BOOT_ID field:

# journalctl _BOOT_ID=156019a44a774a0bb0148a92df4af81b

11.3.2 Filtering Based on Time Interval

You can filter the output of journalctl by specifying the starting and/or ending date. The date specification should be of the format "2014-06-30 9:17:16". If the time part is omitted, midnight is assumed. If seconds are omitted, ":00" is assumed. If the date part is omitted, the current day is assumed. Instead of numeric expression, you can specify the keywords "yesterday", "today", or "tomorrow", which refer to midnight of the day before the current day, of the current day, or of the day after the current day. If you specify "now", it refers to the current time. You can also specify relative times prefixed with - or +, referring to times before or after the current time.

Show only new messages since now, and update the output continuously:

# journalctl --since "now" -f

Show all messages since last midnight till 3:20am:

# journalctl --since "today" --until "3:20"

11.3.3 Filtering Based on Fields

You can filter the output of the journal by specific fields. The syntax of a field to be matched is FIELD_NAME=MATCHED_VALUE, such as _SYSTEMD_UNIT=httpd.service. You can specify multiple matches in a single query to filter the output messages even more. See man 7 systemd.journal-fields for a list of default fields.

Show messages produced by a specific process ID:

# journalctl _PID=1039

Show messages belonging to a specific user ID:

# journalctl _UID=1000

Show messages from the kernel ring buffer (the same as dmesg produces):

# journalctl _TRANSPORT=kernel

Show messages from the service's standard or error output:

# journalctl _TRANSPORT=stdout

Show messages produced by a specified service only:

# journalctl _SYSTEMD_UNIT=avahi-daemon.service

If two different fields are specified, only entries that match both expressions at the same time are shown:

# journalctl _SYSTEMD_UNIT=avahi-daemon.service _PID=1488

If two matches refer to the same field, all entries matching either expression are shown:

# journalctl _SYSTEMD_UNIT=avahi-daemon.service _SYSTEMD_UNIT=dbus.service

You can use the '+' separator to combine two expressions in a logical 'OR'. The following example shows all messages from the Avahi service process with the process ID 1480 together with all messages from the D-Bus service:

# journalctl _SYSTEMD_UNIT=avahi-daemon.service _PID=1480 + _SYSTEMD_UNIT=dbus.service

11.4 Investigating systemd Errors

This section introduces a simple example to illustrate how to find and fix the error reported by systemd during apache2 start-up.

  1. Try to start the apache2 service:

    # systemctl start apache2
    Job for apache2.service failed. See 'systemctl status apache2' and 'journalctl -xn' for details.
  2. Let us see what the service's status says:

    # systemctl status apache2
    apache2.service - The Apache Webserver
       Loaded: loaded (/usr/lib/systemd/system/apache2.service; disabled)
       Active: failed (Result: exit-code) since Tue 2014-06-03 11:08:13 CEST; 7min ago
      Process: 11026 ExecStop=/usr/sbin/start_apache2 -D SYSTEMD -DFOREGROUND \
               -k graceful-stop (code=exited, status=1/FAILURE)

    The ID of the process causing the failure is 11026.

  3. Show the verbose version of messages related to process ID 11026:

    # journalctl -o verbose _PID=11026
    MESSAGE=AH00526: Syntax error on line 6 of /etc/apache2/default-server.conf:
    MESSAGE=Invalid command 'DocumenttRoot', perhaps misspelled or defined by a module
  4. Fix the typo inside /etc/apache2/default-server.conf, start the apache2 service, and print its status:

    # systemctl start apache2 && systemctl status apache2
    apache2.service - The Apache Webserver
       Loaded: loaded (/usr/lib/systemd/system/apache2.service; disabled)
       Active: active (running) since Tue 2014-06-03 11:26:24 CEST; 4ms ago
      Process: 11026 ExecStop=/usr/sbin/start_apache2 -D SYSTEMD -DFOREGROUND
               -k graceful-stop (code=exited, status=1/FAILURE)
     Main PID: 11263 (httpd2-prefork)
       Status: "Processing requests..."
       CGroup: /system.slice/apache2.service
               ├─11263 /usr/sbin/httpd2-prefork -f /etc/apache2/httpd.conf -D [...]
               ├─11280 /usr/sbin/httpd2-prefork -f /etc/apache2/httpd.conf -D [...]
               ├─11281 /usr/sbin/httpd2-prefork -f /etc/apache2/httpd.conf -D [...]
               ├─11282 /usr/sbin/httpd2-prefork -f /etc/apache2/httpd.conf -D [...]
               ├─11283 /usr/sbin/httpd2-prefork -f /etc/apache2/httpd.conf -D [...]
               └─11285 /usr/sbin/httpd2-prefork -f /etc/apache2/httpd.conf -D [...]

11.5 Journald Configuration

The behavior of the systemd-journald service can be adjusted by modifying /etc/systemd/journald.conf. This section introduces only basic option settings. For a complete file description, see man 5 journald.conf. Note that you need to restart the journal for the changes to take effect with

# systemctl restart systemd-journald

11.5.1 Changing the Journal Size Limit

If the journal log data is saved to a persistent location (see Section 11.1, “Making the Journal Persistent”), it uses up to 10% of the file system the /var/log/journal resides on. For example, if /var/log/journal is located on a 30 GB /var partition, the journal may use up to 3 GB of the disk space. To change this limit, change (and uncomment) the SystemMaxUse option:


11.5.2 Forwarding the Journal to /dev/ttyX

You can forward the journal to a terminal device to inform you about system messages on a preferred terminal screen, for example /dev/tty12. Change the following journald options to


11.5.3 Forwarding the Journal to Syslog Facility

Journald is backward compatible with traditional syslog implementations such as rsyslog. Make sure the following is valid:

  • rsyslog is installed.

    # rpm -q rsyslog
  • rsyslog service is enabled.

    # systemctl is-enabled rsyslog
  • Forwarding to syslog is enabled in /etc/systemd/journald.conf.


11.6 Using YaST to Filter the systemd Journal

For an easy way of filtering the systemd journal (without having to deal with the journalctl syntax), you can use the YaST journal module. After installing it with sudo zypper in yast2-journal, start it from YaST by selecting System › Systemd Journal. Alternatively, start it from command line by entering sudo yast2 journal.

YaST systemd Journal
Figure 11.1: YaST systemd Journal

The module displays the log entries in a table. The search box on top allows you to search for entries that contain certain characters, similar to using grep. To filter the entries by date and time, unit, file, or priority, click Change filters and set the respective options.

12 The Boot Loader GRUB 2


This chapter describes how to configure GRUB 2, the boot loader used in openSUSE® Leap. It is the successor of the traditional GRUB boot loader—now called GRUB Legacy. A YaST module is available for configuring the most important settings. The boot procedure as a whole is outlined in Chapter 9, Booting a Linux System. For details on Secure Boot support for UEFI machines, see Chapter 14, UEFI (Unified Extensible Firmware Interface).

12.1 Main Differences between GRUB Legacy and GRUB 2

  • The configuration is stored in different files.

  • More file systems are supported (for example, Btrfs).

  • Can directly read files stored on LVM or RAID devices.

  • The user interface can be translated and altered with themes.

  • Includes a mechanism for loading modules to support additional features, such as file systems, etc.

  • Automatically searches for and generates boot entries for other kernels and operating systems, such as Windows.

  • Includes a minimal Bash-like console.

12.2 Configuration File Structure

The configuration of GRUB 2 is based on the following files:


This file contains the configuration of the GRUB 2 menu items. It replaces menu.lst used in GRUB Legacy. grub.cfg is automatically generated by the grub2-mkconfig command, and should not be edited.


This optional file is directly sourced by grub.cfg at boot time and can be used to add custom items to the boot menu. Starting with openSUSE Leap Leap 42.2 these entries will also be parsed when using grub-once.


This file controls the user settings of GRUB 2 and usually includes additional environmental settings such as backgrounds and themes.

Scripts under /etc/grub.d/

The scripts in this directory are read during execution of the grub2-mkconfig command. Their instructions are integrated into the main configuration file /boot/grub/grub.cfg.


This configuration file is used when configuring the boot loader with YaST and every time a new kernel is installed. It is evaluated by the perl-bootloader which modifies the boot loader configuration file (for example /boot/grub2/grub.cfg for GRUB 2) accordingly. /etc/sysconfig/bootloader is not a GRUB 2-specific configuration file—the values are applied to any boot loader installed on openSUSE Leap.

/boot/grub2/x86_64-efi, ,

These configuration files contain architecture-specific options.

GRUB 2 can be controlled in various ways. Boot entries from an existing configuration can be selected from the graphical menu (splash screen). The configuration is loaded from the file /boot/grub2/grub.cfg which is compiled from other configuration files (see below). All GRUB 2 configuration files are considered system files, and you need root privileges to edit them.

Note: Activating Configuration Changes

After having manually edited GRUB 2 configuration files, you need to run grub2-mkconfig to activate the changes. However, this is not necessary when changing the configuration with YaST, since it will automatically run grub2-mkconfig .

12.2.1 The File /boot/grub2/grub.cfg

The graphical splash screen with the boot menu is based on the GRUB 2 configuration file /boot/grub2/grub.cfg, which contains information about all partitions or operating systems that can be booted by the menu.

Every time the system is booted, GRUB 2 loads the menu file directly from the file system. For this reason, GRUB 2 does not need to be re-installed after changes to the configuration file. grub.cfg is automatically rebuilt with kernel installations or removals.

grub.cfg is compiled by the grub2-mkconfig from the file /etc/default/grub and scripts found in the /etc/grub.d/ directory. Therefore you should never edit the file manually. Instead, edit the related source files or use the YaST Boot Loader module to modify the configuration as described in Section 12.3, “Configuring the Boot Loader with YaST”.

12.2.2 The File /etc/default/grub

More general options of GRUB 2 belong here, such as the time the menu is displayed, or the default OS to boot. To list all available options, see the output of the following command:

grep "export GRUB_DEFAULT" -A50 /usr/sbin/grub2-mkconfig | grep GRUB_

In addition to already defined variables, the user may introduce their own variables, and use them later in the scripts found in the /etc/grub.d directory.

After having edited /etc/default/grub, run grub2-mkconfig to update the main configuration file.

Note: Scope

All options set in this file are general options that affect all boot entries. Specific options for Xen Kernels or the Xen hypervisor can be set via the GRUB_*_XEN_* configuration options. See below for details.


Sets the boot menu entry that is booted by default. Its value can be a numeric value, the complete name of a menu entry, or saved.

GRUB_DEFAULT=2 boots the third (counted from zero) boot menu entry.

GRUB_DEFAULT="2>0" boots the first submenu entry of the third top-level menu entry.

GRUB_DEFAULT="Example boot menu entry" boots the menu entry with the title Example boot menu entry.

GRUB_DEFAULT=saved boots the entry specified by the grub2-reboot or grub2-set-default commands. While grub2-reboot sets the default boot entry for the next reboot only, grub2-set-default sets the default boot entry until changed.


Waits the specified number of seconds for the user to press a key. During the period no menu is shown unless the user presses a key. If no key is pressed during the time specified, the control is passed to GRUB_TIMEOUT. GRUB_HIDDEN_TIMEOUT=0 first checks whether Shift is pressed and shows the boot menu if yes, otherwise immediately boots the default menu entry. This is the default when only one bootable OS is identified by GRUB 2.


If false is specified, a countdown timer is displayed on a blank screen when the GRUB_HIDDEN_TIMEOUT feature is active.


Time period in seconds the boot menu is displayed before automatically booting the default boot entry. If you press a key, the timeout is cancelled and GRUB 2 waits for you to make the selection manually. GRUB_TIMEOUT=-1 will cause the menu to be displayed until you select the boot entry manually.


Entries on this line are added at the end of the boot entries for normal and recovery mode. Use it to add kernel parameters to the boot entry.


Same as GRUB_CMDLINE_LINUX but the entries are appended in the normal mode only.


Same as GRUB_CMDLINE_LINUX but the entries are appended in the recovery mode only.


This entry will completely replace the GRUB_CMDLINE_LINUX parameters for all Xen boot entries.


Same as GRUB_CMDLINE_LINUX_XEN_REPLACE but it will only replace parameters ofGRUB_CMDLINE_LINUX_DEFAULT.


This entry specifies the kernel parameters for the Xen guest kernel only—the operation principle is the same as for GRUB_CMDLINE_LINUX.


Same as GRUB_CMDLINE_XEN—the operation principle is the same as for GRUB_CMDLINE_LINUX_DEFAULT.


Enables and specifies an input/output terminal device. Can be console (PC BIOS and EFI consoles), serial (serial terminal), ofconsole (Open Firmware console), or the default gfxterm (graphics-mode output). It is also possible to enable more than one device by quoting the required options, for example GRUB_TERMINAL="console serial".


The resolution used for the gfxterm graphical terminal. Note that you can only use modes supported by your graphics card (VBE). The default is ‘auto’, which tries to select a preferred resolution. You can display the screen resolutions available to GRUB 2 by typing vbeinfo in the GRUB 2 command line. The command line is accessed by typing C when the GRUB 2 boot menu screen is displayed.

You can also specify a color depth by appending it to the resolution setting, for example GRUB_GFXMODE=1280x1024x24.


Set a background image for the gfxterm graphical terminal. The image must be a file readable by GRUB 2 at boot time, and it must end with the .png, .tga, .jpg, or .jpeg suffix. If necessary, the image will be scaled to fit the screen.


If this option is set to true, automatic searching for other operating systems is disabled. Only the kernel images in /boot/ and the options from your own scripts in /etc/grub.d/ are detected.


If this option is set to true, GRUB 2 can boot directly into Snapper snapshots. For more information, see Section 3.3, “System Rollback by Booting from Snapshots”.

Note: Parameter Handling

All *_DEFAULT parameters can be configured manually or with YaST.

For a complete list of options, see the GNU GRUB manual. For a complete list of possible parameters, see

12.2.3 Scripts in /etc/grub.d

The scripts in this directory are read during execution of the grub2-mkconfig command, and their instructions are incorporated into /boot/grub2/grub.cfg. The order of menu items in grub.cfg is determined by the order in which the files in this directory are run. Files with a leading numeral are executed first, beginning with the lowest number. 00_header is run before 10_linux, which would run before 40_custom. If files with alphabetic names are present, they are executed after the numerically-named files. Only executable files generate output to grub.cfg during execution of grub2-mkconfig. By default all files in the /etc/grub.d directory are executable. The most important scripts are:


Sets environmental variables such as system file locations, display settings, themes, and previously saved entries. It also imports preferences stored in the /etc/default/grub. Normally you do not need to make changes to this file.


Identifies Linux kernels on the root device and creates relevant menu entries. This includes the associated recovery mode option if enabled. Only the latest kernel is displayed on the main menu page, with additional kernels included in a submenu.


This script uses OS-prober to search for Linux and other operating systems and places the results in the GRUB 2 menu. There are sections to identify specific other operating systems, such as Windows or macOS.


This file provides a simple way to include custom boot entries into grub.cfg. Make sure that you do not change the exec tail -n +3 $0 part at the beginning.


This is a special script that copies a corresponding part of the grub.cfg file and outputs it back unchanged. This way you can modify that part of grub.cfg directly and the change survives the execution of grub2-mkconfig .

The processing sequence is set by the preceding numbers with the lowest number being executed first. If scripts are preceded by the same number the alphabetical order of the complete name decides the order.

12.2.4 Mapping between BIOS Drives and Linux Devices

In GRUB Legacy, the configuration file was used to derive Linux device names from BIOS drive numbers. The mapping between BIOS drives and Linux devices cannot always be guessed correctly. For example, GRUB Legacy would get a wrong order if the boot sequence of IDE and SCSI drives is exchanged in the BIOS configuration.

GRUB 2 avoids this problem by using device ID strings (UUIDs) or file system labels when generating grub.cfg. GRUB 2 utilities create a temporary device map on the fly, which is usually sufficient, particularly in the case of single-disk systems.

However, if you need to override the GRUB 2's automatic device mapping mechanism, create your custom mapping file /boot/grub2/ The following example changes the mapping to make DISK 3 the boot disk. Note that GRUB 2 partition numbers start with 1 and not with 0 as in GRUB Legacy.

(hd1)  /dev/disk-by-id/DISK3 ID
(hd2)  /dev/disk-by-id/DISK1 ID
(hd3)  /dev/disk-by-id/DISK2 ID

12.2.5 Editing Menu Entries during the Boot Procedure

Being able to directly edit menu entries is useful when the system does not boot anymore because of a faulty configuration. It can also be used to test new settings without altering the system configuration.

  1. In the graphical boot menu, select the entry you want to edit with the arrow keys.

  2. Press E to open the text-based editor.

  3. Use the arrow keys to move to the line you want to edit.

    GRUB 2 Boot Editor
    Figure 12.1: GRUB 2 Boot Editor

    Now you have two options:

    1. Add space-separated parameters to the end of the line starting with linux or linuxefi to edit the kernel parameters. A complete list of parameters is available at

    2. Or edit the general options to change for example the kernel version. The →| key suggests all possible completions.

  4. Press F10 to boot the system with the changes you made or press Esc to discard your edits and return to the GRUB 2 menu.

Changes made this way only apply to the current boot process and are not saved permanently.

Important: Keyboard Layout During the Boot Procedure

The US keyboard layout is the only one available when booting. See Book “Start-Up”, Chapter 16 “Common Problems and Their Solutions”, Section 16.2.3 “Booting from Installation Media Fails”, US Keyboard Layout.

Note: Boot Loader on the Installation Media

The Boot Loader of the installation media on systems with a traditional BIOS is still GRUB Legacy. To add boot options, select an entry and start typing. Additions you make to the installation boot entry will be permanently saved in the installed system.

12.2.6 Setting a Boot Password

Even before the operating system is booted, GRUB 2 enables access to file systems. Users without root permissions can access files in your Linux system to which they have no access after the system is booted. To block this kind of access or to prevent users from booting certain menu entries, set a boot password.

Important: Booting Requires Password

If set, the boot password is required on every boot, which means the system does not boot automatically.

Proceed as follows to set a boot password. Alternatively use YaST (Protect Boot Loader with Password ).

  1. Encrypt the password using grub2-mkpasswd-pbkdf2:

    tux >  sudo grub2-mkpasswd-pbkdf2
    Password: ****
    Reenter password: ****
    PBKDF2 hash of your password is grub.pbkdf2.sha512.10000.9CA4611006FE96BC77A...
  2. Paste the resulting string into the file /etc/grub.d/40_custom together with the set superusers command.

    set superusers="root"
    password_pbkdf2 root grub.pbkdf2.sha512.10000.9CA4611006FE96BC77A...
  3. Run grub2-mkconfig to import the changes into the main configuration file.

After you reboot, you will be prompted for a user name and a password when trying to boot a menu entry. Enter root and the password you typed during the grub2-mkpasswd-pbkdf2 command. If the credentials are correct, the system will boot the selected boot entry.

For more information, see

12.3 Configuring the Boot Loader with YaST

The easiest way to configure general options of the boot loader in your openSUSE Leap system is to use the YaST module. In the YaST Control Center, select System › Boot Loader. The module shows the current boot loader configuration of your system and allows you to make changes.

Use the Boot Code Options tab to view and change settings related to type, location and advanced loader settings. You can choose whether to use GRUB 2 in standard or EFI mode.

Boot Code Options
Figure 12.2: Boot Code Options
Important: EFI Systems require GRUB2-EFI

If you have an EFI system you can only install GRUB2-EFI, otherwise your system is no longer bootable.

Important: Reinstalling the Boot Loader

To reinstall the boot loader, make sure to change a setting in YaST and then change it back. For example, to reinstall GRUB2-EFI, select GRUB2 first and then immediately switch back to GRUB2-EFI.

Otherwise, the boot loader may only be partially reinstalled.

Note: Custom Boot Loader

To use a boot loader other than the ones listed, select Do Not Install Any Boot Loader. Read the documentation of your boot loader carefully before choosing this option.

12.3.1 Modifying the Boot Loader Location

To modify the location of the boot loader, follow these steps:

Procedure 12.1: Changing the Boot Loader Location
  1. Select the Boot Code Options tab and then choose one of the following options for Boot Loader Location:

    Boot from Master Boot Record

    This installs the boot loader in the MBR of the first disk (according to the boot sequence preset in the BIOS).

    Boot from Root Partition

    This installs the boot loader in the boot sector of the / partition (this is the default).

    Custom Boot Partition

    Use this option to specify the location of the boot loader manually.

  2. Click OK to apply your changes.

12.3.2 Adjusting the Disk Order

If your computer has more than one hard disk, you can specify the boot sequence of the disks. For more information, see Section 12.2.4, “Mapping between BIOS Drives and Linux Devices”.

Procedure 12.2: Setting the Disk Order
  1. Open the Boot Code Options tab.

  2. Click Boot Loader Installation Details.

  3. If more than one disk is listed, select a disk and click Up or Down to reorder the displayed disks.

  4. Click OK two times to save the changes.

12.3.3 Configuring Advanced Options

Advanced boot options can be configured via the Boot Loader Options tab. Boot Loader Options Tab

Boot loader Options
Figure 12.3: Boot loader Options
Boot Loader Time-Out

Change the value of Time-Out in Seconds by typing in a new value and clicking the appropriate arrow key with your mouse.

Probe Foreign OS

When selected, the boot loader searches for other systems like Windows or other Linux installations.

Hide Menu on Boot

Hides the boot menu and boots the default entry.

Adjusting the Default Boot Entry

Select the desired entry from the Default Boot Section list. Note that the > sign in the boot entry name delimits the boot section and its subsection.

Protect Boot Loader with Password

Protects the boot loader and the system with an additional password. For more information, see Section 12.2.6, “Setting a Boot Password”. Kernel Parameters Tab

Kernel Parameters
Figure 12.4: Kernel Parameters
VGA Mode

The VGA Mode option specifies the default screen resolution during the boot process.

Kernel Command Line Parameter

The optional kernel parameters are added at the end of the default parameters. For a list of all possible parameters, see

Use graphical console

When checked, the boot menu appears on a graphical splash screen rather than in a text mode. The resolution of the boot screen can be then set from the Console resolution list, and graphical theme definition file can be specified with the Console theme file-chooser.

Use Serial Console

If your machine is controlled via a serial console, activate this option and specify which COM port to use at which speed. See info grub or Boot Code Options Tab

Code Options
Figure 12.5: Code Options
Set Active Flag in Partition Table for Boot Partition

Activates the partition that contains the boot loader. Some legacy operating systems (such as Windows) can only boot from an active partition.

Write Generic Boot Code to MBR

Replaces the current MBR with generic, operating system independent code.

Enable Trusted Boot Support

Starts TrustedGRUB2 which supports trusted computing functionality (Trusted Platform Module (TPM)). For more information refer to

12.4 Differences in Terminal Usage on z Systems

On 3215 and 3270 terminals there are some differences and limitations on how to move the cursor and how to issue editing commands within GRUB 2.

12.4.1 Limitations


Interactivity is strongly limited. Typing often does not result in visual feedback. To see where the cursor is, type an underscore (_).

Note: 3270 Compared to 3215

The 3270 terminal is much better at displaying and refreshing screens than the 3215 terminal.

Cursor Movement

Traditional cursor movement is not possible. Alt, Meta, Ctrl and the cursor keys do not work. To move the cursor, use the key combinations listed in Section 12.4.2, “Key Combinations”.


The caret (^) is used as a control character. To type a literal ^ followed by a letter, type ^, ^, LETTER.


The Enter key does not work, use ^J instead.

12.4.2 Key Combinations

Common Substitutes:


engage (Enter)


abort, return to previous state


tab completion (in edit and shell mode)

Keys Available in Menu Mode:


first entry


last entry


previous entry


next entry


previous page


next page


boot selected entry or enter submenu (same as ^J)


edit selected entry


enter GRUB-Shell

Keys Available in Edit Mode:


previous line


next line


backward char


forward char


beginning of line


end of line






kill line




open line


refresh screen


boot entry


enter GRUB-Shell

Keys Available in Command Line Mode:


previous command


next command from history


beginning of line


end of line


backward char


forward char






kill line


discard line



12.5 Helpful GRUB 2 Commands


Generates a new /boot/grub2/grub.cfg based on /etc/default/grub and the scripts from /etc/grub.d/.

Example 12.1: Usage of grub2-mkconfig
grub2-mkconfig -o /boot/grub2/grub.cfg
Tip: Syntax Check

Running grub2-mkconfig without any parameters prints the configuration to STDOUT where it can be reviewed. Use grub2-script-check after /boot/grub2/grub.cfg has been written to check its syntax.

Important: grub2-mkconfig Cannot Repair UEFI Secure Boot Tables

If you are using UEFI Secure Boot and your system is not reaching GRUB 2 correctly anymore, you may need to additionally reinstall Shim and regenerate the UEFI boot table. To do so, use:

root # shim-install --config-file=/boot/grub2/grub.cfg

Creates a bootable rescue image of your installed GRUB 2 configuration.

Example 12.2: Usage of grub2-mkrescue
grub2-mkrescue -o save_path/name.iso iso

Checks the given file for syntax errors.

Example 12.3: Usage of grub2-script-check
grub2-check-config /boot/grub2/grub.cfg

Set the default boot entry for the next boot only. To get the list of available boot entries use the --list option.

Example 12.4: Usage of grub2-once
grub2-once number_of_the_boot_entry
Tip: grub2-once Help

Call the program without any option to get a full list of all possible options.

12.6 More Information

Extensive information about GRUB 2 is available at Also refer to the grub info page. You can also search for the keyword GRUB 2 in the Technical Information Search at to get information about special issues.

13 Basic Networking


Linux offers the necessary networking tools and features for integration into all types of network structures. Network access using a network card can be configured with YaST. Manual configuration is also possible. In this chapter only the fundamental mechanisms and the relevant network configuration files are covered.

Linux and other Unix operating systems use the TCP/IP protocol. It is not a single network protocol, but a family of network protocols that offer various services. The protocols listed in Several Protocols in the TCP/IP Protocol Family, are provided for exchanging data between two machines via TCP/IP. Networks combined by TCP/IP, comprising a worldwide network, are also called the Internet.

RFC stands for Request for Comments. RFCs are documents that describe various Internet protocols and implementation procedures for the operating system and its applications. The RFC documents describe the setup of Internet protocols. For more information about RFCs, see

Several Protocols in the TCP/IP Protocol Family

Transmission Control Protocol: a connection-oriented secure protocol. The data to transmit is first sent by the application as a stream of data and converted into the appropriate format by the operating system. The data arrives at the respective application on the destination host in the original data stream format it was initially sent. TCP determines whether any data has been lost or jumbled during the transmission. TCP is implemented wherever the data sequence matters.


User Datagram Protocol: a connectionless, insecure protocol. The data to transmit is sent in the form of packets generated by the application. The order in which the data arrives at the recipient is not guaranteed and data loss is possible. UDP is suitable for record-oriented applications. It features a smaller latency period than TCP.


Internet Control Message Protocol: Essentially, this is not a protocol for the end user, but a special control protocol that issues error reports and can control the behavior of machines participating in TCP/IP data transfer. In addition, it provides a special echo mode that can be viewed using the program ping.


Internet Group Management Protocol: This protocol controls machine behavior when implementing IP multicast.

As shown in Figure 13.1, “Simplified Layer Model for TCP/IP”, data exchange takes place in different layers. The actual network layer is the insecure data transfer via IP (Internet protocol). On top of IP, TCP (transmission control protocol) guarantees, to a certain extent, security of the data transfer. The IP layer is supported by the underlying hardware-dependent protocol, such as Ethernet.

Simplified Layer Model for TCP/IP
Figure 13.1: Simplified Layer Model for TCP/IP

The diagram provides one or two examples for each layer. The layers are ordered according to abstraction levels. The lowest layer is very close to the hardware. The uppermost layer, however, is almost a complete abstraction from the hardware. Every layer has its own special function. The special functions of each layer are mostly implicit in their description. The data link and physical layers represent the physical network used, such as Ethernet.

Almost all hardware protocols work on a packet-oriented basis. The data to transmit is collected into packets (it cannot be sent all at once). The maximum size of a TCP/IP packet is approximately 64 KB. Packets are normally quite smaller, as the network hardware can be a limiting factor. The maximum size of a data packet on an Ethernet is about fifteen hundred bytes. The size of a TCP/IP packet is limited to this amount when the data is sent over an Ethernet. If more data is transferred, more data packets need to be sent by the operating system.

For the layers to serve their designated functions, additional information regarding each layer must be saved in the data packet. This takes place in the header of the packet. Every layer attaches a small block of data, called the protocol header, to the front of each emerging packet. A sample TCP/IP data packet traveling over an Ethernet cable is illustrated in Figure 13.2, “TCP/IP Ethernet Packet”. The proof sum is located at the end of the packet, not at the beginning. This simplifies things for the network hardware.

TCP/IP Ethernet Packet
Figure 13.2: TCP/IP Ethernet Packet

When an application sends data over the network, the data passes through each layer, all implemented in the Linux Kernel except the physical layer. Each layer is responsible for preparing the data so it can be passed to the next layer. The lowest layer is ultimately responsible for sending the data. The entire procedure is reversed when data is received. Like the layers of an onion, in each layer the protocol headers are removed from the transported data. Finally, the transport layer is responsible for making the data available for use by the applications at the destination. In this manner, one layer only communicates with the layer directly above or below it. For applications, it is irrelevant whether data is transmitted via a 100 Mbit/s FDDI network or via a 56-Kbit/s modem line. Likewise, it is irrelevant for the data line which kind of data is transmitted, as long as packets are in the correct format.

13.1 IP Addresses and Routing

The discussion in this section is limited to IPv4 networks. For information about IPv6 protocol, the successor to IPv4, refer to Section 13.2, “IPv6—The Next Generation Internet”.

13.1.1 IP Addresses

Every computer on the Internet has a unique 32-bit address. These 32 bits (or 4 bytes) are normally written as illustrated in the second row in Example 13.1, “Writing IP Addresses”.

Example 13.1: Writing IP Addresses
IP Address (binary):  11000000 10101000 00000000 00010100
IP Address (decimal):      192.     168.       0.      20

In decimal form, the four bytes are written in the decimal number system, separated by periods. The IP address is assigned to a host or a network interface. It can be used only once throughout the world. There are exceptions to this rule, but these are not relevant to the following passages.

The points in IP addresses indicate the hierarchical system. Until the 1990s, IP addresses were strictly categorized in classes. However, this system proved too inflexible and was discontinued. Now, classless routing (CIDR, classless interdomain routing) is used.

13.1.2 Netmasks and Routing

Netmasks are used to define the address range of a subnet. If two hosts are in the same subnet, they can reach each other directly. If they are not in the same subnet, they need the address of a gateway that handles all the traffic for the subnet. To check if two IP addresses are in the same subnet, simply AND both addresses with the netmask. If the result is identical, both IP addresses are in the same local network. If there are differences, the remote IP address, and thus the remote interface, can only be reached over a gateway.

To understand how the netmask works, look at Example 13.2, “Linking IP Addresses to the Netmask”. The netmask consists of 32 bits that identify how much of an IP address belongs to the network. All those bits that are 1 mark the corresponding bit in the IP address as belonging to the network. All bits that are 0 mark bits inside the subnet. This means that the more bits are 1, the smaller the subnet is. Because the netmask always consists of several successive 1 bits, it is also possible to count the number of bits in the netmask. In Example 13.2, “Linking IP Addresses to the Netmask” the first net with 24 bits could also be written as

Example 13.2: Linking IP Addresses to the Netmask
IP address (  11000000 10101000 00000000 00010100
Netmask   (  11111111 11111111 11111111 00000000
Result of the link:         11000000 10101000 00000000 00000000
In the decimal system:           192.     168.       0.       0

IP address ( 11010101 10111111 00001111 11001000
Netmask    ( 11111111 11111111 11111111 00000000
Result of the link:         11010101 10111111 00001111 00000000
In the decimal system:           213.      95.      15.       0

To give another example: all machines connected with the same Ethernet cable are usually located in the same subnet and are directly accessible. Even when the subnet is physically divided by switches or bridges, these hosts can still be reached directly.

IP addresses outside the local subnet can only be reached if a gateway is configured for the target network. In the most common case, there is only one gateway that handles all traffic that is external. However, it is also possible to configure several gateways for different subnets.

If a gateway has been configured, all external IP packets are sent to the appropriate gateway. This gateway then attempts to forward the packets in the same manner—from host to host—until it reaches the destination host or the packet's TTL (time to live) expires.

Specific Addresses
Base Network Address

This is the netmask AND any address in the network, as shown in Example 13.2, “Linking IP Addresses to the Netmask” under Result. This address cannot be assigned to any hosts.

Broadcast Address

This could be paraphrased as: Access all hosts in this subnet. To generate this, the netmask is inverted in binary form and linked to the base network address with a logical OR. The above example therefore results in This address cannot be assigned to any hosts.

Local Host

The address is assigned to the loopback device on each host. A connection can be set up to your own machine with this address and with all addresses from the complete loopback network as defined with IPv4. With IPv6 there is only one loopback address (::1).

Because IP addresses must be unique all over the world, you cannot select random addresses. There are three address domains to use if you want to set up a private IP-based network. These cannot get any connection from the rest of the Internet, because they cannot be transmitted over the Internet. These address domains are specified in RFC 1597 and listed in Table 13.1, “Private IP Address Domains”.

Table 13.1: Private IP Address Domains






13.2 IPv6—The Next Generation Internet

Because of the emergence of the WWW (World Wide Web), the Internet has experienced explosive growth, with an increasing number of computers communicating via TCP/IP in the past fifteen years. Since Tim Berners-Lee at CERN ( invented the WWW in 1990, the number of Internet hosts has grown from a few thousand to about a hundred million.

As mentioned, an IPv4 address consists of only 32 bits. Also, quite a few IP addresses are lost—they cannot be used because of the way in which networks are organized. The number of addresses available in your subnet is two to the power of the number of bits, minus two. A subnet has, for example, 2, 6, or 14 addresses available. To connect 128 hosts to the Internet, for example, you need a subnet with 256 IP addresses, from which only 254 are usable, because two IP addresses are needed for the structure of the subnet itself: the broadcast and the base network address.

Under the current IPv4 protocol, DHCP or NAT (network address translation) are the typical mechanisms used to circumvent the potential address shortage. Combined with the convention to keep private and public address spaces separate, these methods can certainly mitigate the shortage. The problem with them lies in their configuration, which is a chore to set up and a burden to maintain. To set up a host in an IPv4 network, you need several address items, such as the host's own IP address, the subnetmask, the gateway address and maybe a name server address. All these items need to be known and cannot be derived from somewhere else.

With IPv6, both the address shortage and the complicated configuration should be a thing of the past. The following sections tell more about the improvements and benefits brought by IPv6 and about the transition from the old protocol to the new one.

13.2.1 Advantages

The most important and most visible improvement brought by the new protocol is the enormous expansion of the available address space. An IPv6 address is made up of 128 bit values instead of the traditional 32 bits. This provides for as many as several quadrillion IP addresses.

However, IPv6 addresses are not only different from their predecessors with regard to their length. They also have a different internal structure that may contain more specific information about the systems and the networks to which they belong. More details about this are found in Section 13.2.2, “Address Types and Structure”.

The following is a list of other advantages of the new protocol:


IPv6 makes the network plug and play capable, which means that a newly set up system integrates into the (local) network without any manual configuration. The new host uses its automatic configuration mechanism to derive its own address from the information made available by the neighboring routers, relying on a protocol called the neighbor discovery (ND) protocol. This method does not require any intervention on the administrator's part and there is no need to maintain a central server for address allocation—an additional advantage over IPv4, where automatic address allocation requires a DHCP server.

Nevertheless if a router is connected to a switch, the router should send periodic advertisements with flags telling the hosts of a network how they should interact with each other. For more information, see RFC 2462 and the radvd.conf(5) man page, and RFC 3315.


IPv6 makes it possible to assign several addresses to one network interface at the same time. This allows users to access several networks easily, something that could be compared with the international roaming services offered by mobile phone companies: when you take your mobile phone abroad, the phone automatically logs in to a foreign service when it enters the corresponding area, so you can be reached under the same number everywhere and can place an outgoing call, as you would in your home area.

Secure Communication

With IPv4, network security is an add-on function. IPv6 includes IPsec as one of its core features, allowing systems to communicate over a secure tunnel to avoid eavesdropping by outsiders on the Internet.

Backward Compatibility

Realistically, it would be impossible to switch the entire Internet from IPv4 to IPv6 at one time. Therefore, it is crucial that both protocols can coexist not only on the Internet, but also on one system. This is ensured by compatible addresses (IPv4 addresses can easily be translated into IPv6 addresses) and by using several tunnels. See Section 13.2.3, “Coexistence of IPv4 and IPv6”. Also, systems can rely on a dual stack IP technique to support both protocols at the same time, meaning that they have two network stacks that are completely separate, such that there is no interference between the two protocol versions.

Custom Tailored Services through Multicasting

With IPv4, some services, such as SMB, need to broadcast their packets to all hosts in the local network. IPv6 allows a much more fine-grained approach by enabling servers to address hosts through multicasting—by addressing several hosts as parts of a group (which is different from addressing all hosts through broadcasting or each host individually through unicasting). Which hosts are addressed as a group may depend on the concrete application. There are some predefined groups to address all name servers (the all name servers multicast group), for example, or all routers (the all routers multicast group).

13.2.2 Address Types and Structure

As mentioned, the current IP protocol is lacking in two important aspects: there is an increasing shortage of IP addresses and configuring the network and maintaining the routing tables is becoming a more complex and burdensome task. IPv6 solves the first problem by expanding the address space to 128 bits. The second one is countered by introducing a hierarchical address structure, combined with sophisticated techniques to allocate network addresses, and multihoming (the ability to assign several addresses to one device, giving access to several networks).

When dealing with IPv6, it is useful to know about three different types of addresses:


Addresses of this type are associated with exactly one network interface. Packets with such an address are delivered to only one destination. Accordingly, unicast addresses are used to transfer packets to individual hosts on the local network or the Internet.


Addresses of this type relate to a group of network interfaces. Packets with such an address are delivered to all destinations that belong to the group. Multicast addresses are mainly used by certain network services to communicate with certain groups of hosts in a well-directed manner.


Addresses of this type are related to a group of interfaces. Packets with such an address are delivered to the member of the group that is closest to the sender, according to the principles of the underlying routing protocol. Anycast addresses are used to make it easier for hosts to find out about servers offering certain services in the given network area. All servers of the same type have the same anycast address. Whenever a host requests a service, it receives a reply from the server with the closest location, as determined by the routing protocol. If this server should fail for some reason, the protocol automatically selects the second closest server, then the third one, and so forth.

An IPv6 address is made up of eight four-digit fields, each representing 16 bits, written in hexadecimal notation. They are separated by colons (:). Any leading zero bytes within a given field may be dropped, but zeros within the field or at its end may not. Another convention is that more than four consecutive zero bytes may be collapsed into a double colon. However, only one such :: is allowed per address. This kind of shorthand notation is shown in Example 13.3, “Sample IPv6 Address”, where all three lines represent the same address.

Example 13.3: Sample IPv6 Address
fe80 : 0000 : 0000 : 0000 : 0000 : 10 : 1000 : 1a4
fe80 :    0 :    0 :    0 :    0 : 10 : 1000 : 1a4
fe80 :                           : 10 : 1000 : 1a4

Each part of an IPv6 address has a defined function. The first bytes form the prefix and specify the type of address. The center part is the network portion of the address, but it may be unused. The end of the address forms the host part. With IPv6, the netmask is defined by indicating the length of the prefix after a slash at the end of the address. An address, as shown in Example 13.4, “IPv6 Address Specifying the Prefix Length”, contains the information that the first 64 bits form the network part of the address and the last 64 form its host part. In other words, the 64 means that the netmask is filled with 64 1-bit values from the left. As with IPv4, the IP address is combined with AND with the values from the netmask to determine whether the host is located in the same subnet or in another one.

Example 13.4: IPv6 Address Specifying the Prefix Length

IPv6 knows about several predefined types of prefixes. Some are shown in Various IPv6 Prefixes.

Various IPv6 Prefixes

IPv4 addresses and IPv4 over IPv6 compatibility addresses. These are used to maintain compatibility with IPv4. Their use still requires a router able to translate IPv6 packets into IPv4 packets. Several special addresses, such as the one for the loopback device, have this prefix as well.

2 or 3 as the first digit

Aggregatable global unicast addresses. As is the case with IPv4, an interface can be assigned to form part of a certain subnet. Currently, there are the following address spaces: 2001::/16 (production quality address space) and 2002::/16 (6to4 address space).


Link-local addresses. Addresses with this prefix should not be routed and should therefore only be reachable from within the same subnet.


Site-local addresses. These may be routed, but only within the network of the organization to which they belong. In effect, they are the IPv6 equivalent of the current private network address space, such as 10.x.x.x.


These are multicast addresses.

A unicast address consists of three basic components:

Public Topology

The first part (which also contains one of the prefixes mentioned above) is used to route packets through the public Internet. It includes information about the company or institution that provides the Internet access.

Site Topology

The second part contains routing information about the subnet to which to deliver the packet.

Interface ID

The third part identifies the interface to which to deliver the packet. This also allows for the MAC to form part of the address. Given that the MAC is a globally unique, fixed identifier coded into the device by the hardware maker, the configuration procedure is substantially simplified. In fact, the first 64 address bits are consolidated to form the EUI-64 token, with the last 48 bits taken from the MAC, and the remaining 24 bits containing special information about the token type. This also makes it possible to assign an EUI-64 token to interfaces that do not have a MAC, such as those based on PPP.

On top of this basic structure, IPv6 distinguishes between five different types of unicast addresses:

:: (unspecified)

This address is used by the host as its source address when the interface is initialized for the first time—when the address cannot yet be determined by other means.

::1 (loopback)

The address of the loopback device.

IPv4 Compatible Addresses

The IPv6 address is formed by the IPv4 address and a prefix consisting of 96 zero bits. This type of compatibility address is used for tunneling (see Section 13.2.3, “Coexistence of IPv4 and IPv6”) to allow IPv4 and IPv6 hosts to communicate with others operating in a pure IPv4 environment.

IPv4 Addresses Mapped to IPv6

This type of address specifies a pure IPv4 address in IPv6 notation.

Local Addresses

There are two address types for local use:


This type of address can only be used in the local subnet. Packets with a source or target address of this type should not be routed to the Internet or other subnets. These addresses contain a special prefix (fe80::/10) and the interface ID of the network card, with the middle part consisting of zero bytes. Addresses of this type are used during automatic configuration to communicate with other hosts belonging to the same subnet.


Packets with this type of address may be routed to other subnets, but not to the wider Internet—they must remain inside the organization's own network. Such addresses are used for intranets and are an equivalent of the private address space defined by IPv4. They contain a special prefix (fec0::/10), the interface ID, and a 16 bit field specifying the subnet ID. Again, the rest is filled with zero bytes.

As a completely new feature introduced with IPv6, each network interface normally gets several IP addresses, with the advantage that several networks can be accessed through the same interface. One of these networks can be configured completely automatically using the MAC and a known prefix with the result that all hosts on the local network can be reached when IPv6 is enabled (using the link-local address). With the MAC forming part of it, any IP address used in the world is unique. The only variable parts of the address are those specifying the site topology and the public topology, depending on the actual network in which the host is currently operating.

For a host to go back and forth between different networks, it needs at least two addresses. One of them, the home address, not only contains the interface ID but also an identifier of the home network to which it normally belongs (and the corresponding prefix). The home address is a static address and, as such, it does not normally change. Still, all packets destined to the mobile host can be delivered to it, regardless of whether it operates in the home network or somewhere outside. This is made possible by the completely new features introduced with IPv6, such as stateless autoconfiguration and neighbor discovery. In addition to its home address, a mobile host gets one or more additional addresses that belong to the foreign networks where it is roaming. These are called care-of addresses. The home network has a facility that forwards any packets destined to the host when it is roaming outside. In an IPv6 environment, this task is performed by the home agent, which takes all packets destined to the home address and relays them through a tunnel. On the other hand, those packets destined to the care-of address are directly transferred to the mobile host without any special detours.

13.2.3 Coexistence of IPv4 and IPv6

The migration of all hosts connected to the Internet from IPv4 to IPv6 is a gradual process. Both protocols will coexist for some time to come. The coexistence on one system is guaranteed where there is a dual stack implementation of both protocols. That still leaves the question of how an IPv6 enabled host should communicate with an IPv4 host and how IPv6 packets should be transported by the current networks, which are predominantly IPv4 based. The best solutions offer tunneling and compatibility addresses (see Section 13.2.2, “Address Types and Structure”).

IPv6 hosts that are more or less isolated in the (worldwide) IPv4 network can communicate through tunnels: IPv6 packets are encapsulated as IPv4 packets to move them across an IPv4 network. Such a connection between two IPv4 hosts is called a tunnel. To achieve this, packets must include the IPv6 destination address (or the corresponding prefix) and the IPv4 address of the remote host at the receiving end of the tunnel. A basic tunnel can be configured manually according to an agreement between the hosts' administrators. This is also called static tunneling.

However, the configuration and maintenance of static tunnels is often too labor-intensive to use them for daily communication needs. Therefore, IPv6 provides for three different methods of dynamic tunneling:


IPv6 packets are automatically encapsulated as IPv4 packets and sent over an IPv4 network capable of multicasting. IPv6 is tricked into seeing the whole network (Internet) as a huge local area network (LAN). This makes it possible to determine the receiving end of the IPv4 tunnel automatically. However, this method does not scale very well and is also hampered because IP multicasting is far from widespread on the Internet. Therefore, it only provides a solution for smaller corporate or institutional networks where multicasting can be enabled. The specifications for this method are laid down in RFC 2529.


With this method, IPv4 addresses are automatically generated from IPv6 addresses, enabling isolated IPv6 hosts to communicate over an IPv4 network. However, several problems have been reported regarding the communication between those isolated IPv6 hosts and the Internet. The method is described in RFC 3056.

IPv6 Tunnel Broker

This method relies on special servers that provide dedicated tunnels for IPv6 hosts. It is described in RFC 3053.

13.2.4 Configuring IPv6

To configure IPv6, you normally do not need to make any changes on the individual workstations. IPv6 is enabled by default. To disable or enable IPv6 on an installed system, use the YaST Network Settings module. On the Global Options tab, check or uncheck the Enable IPv6 option as necessary. If you want to enable it temporarily until the next reboot, enter modprobe -i ipv6 as root. It is impossible to unload the IPv6 module after is has been loaded.

Because of the autoconfiguration concept of IPv6, the network card is assigned an address in the link-local network. Normally, no routing table management takes place on a workstation. The network routers can be queried by the workstation, using the router advertisement protocol, for what prefix and gateways should be implemented. The radvd program can be used to set up an IPv6 router. This program informs the workstations which prefix to use for the IPv6 addresses and which routers. Alternatively, use zebra/quagga for automatic configuration of both addresses and routing.

For information about how to set up various types of tunnels using the /etc/sysconfig/network files, see the man page of ifcfg-tunnel (man ifcfg-tunnel).

13.2.5 For More Information

The above overview does not cover the topic of IPv6 comprehensively. For a more in-depth look at the new protocol, refer to the following online documentation and books:

The starting point for everything about IPv6.

All information needed to start your own IPv6 network.

The list of IPv6-enabled products.

Here, find the Linux IPv6-HOWTO and many links related to the topic.

RFC 2640

The fundamental RFC about IPv6.

IPv6 Essentials

A book describing all the important aspects of the topic is IPv6 Essentials by Silvia Hagen (ISBN 0-596-00125-8).

13.3 Name Resolution

DNS assists in assigning an IP address to one or more names and assigning a name to an IP address. In Linux, this conversion is usually carried out by a special type of software known as bind. The machine that takes care of this conversion is called a name server. The names make up a hierarchical system in which each name component is separated by a period. The name hierarchy is, however, independent of the IP address hierarchy described above.

Consider a complete name, such as, written in the format hostname.domain. A full name, called a fully qualified domain name (FQDN), consists of a host name and a domain name ( The latter also includes the top level domain or TLD (com).

TLD assignment has become quite confusing for historical reasons. Traditionally, three-letter domain names are used in the USA. In the rest of the world, the two-letter ISO national codes are the standard. In addition to that, longer TLDs were introduced in 2000 that represent certain spheres of activity (for example, .info, .name, .museum).

In the early days of the Internet (before 1990), the file /etc/hosts was used to store the names of all the machines represented over the Internet. This quickly proved to be impractical in the face of the rapidly growing number of computers connected to the Internet. For this reason, a decentralized database was developed to store the host names in a widely distributed manner. This database, similar to the name server, does not have the data pertaining to all hosts in the Internet readily available, but can dispatch requests to other name servers.

The top of the hierarchy is occupied by root name servers. These root name servers manage the top level domains and are run by the Network Information Center (NIC). Each root name server knows about the name servers responsible for a given top level domain. Information about top level domain NICs is available at

DNS can do more than resolve host names. The name server also knows which host is receiving e-mails for an entire domain—the mail exchanger (MX).

For your machine to resolve an IP address, it must know about at least one name server and its IP address. Easily specify such a name server using YaST. The configuration of name server access with openSUSE® Leap is described in Section, “Configuring Host Name and DNS”. Setting up your own name server is described in Chapter 19, The Domain Name System.

The protocol whois is closely related to DNS. With this program, quickly find out who is responsible for a given domain.

Note: MDNS and .local Domain Names

The .local top level domain is treated as link-local domain by the resolver. DNS requests are send as multicast DNS requests instead of normal DNS requests. If you already use the .local domain in your name server configuration, you must switch this option off in /etc/host.conf. For more information, see the host.conf manual page.

If you want to switch off MDNS during installation, use nomdns=1 as a boot parameter.

For more information on multicast DNS, see

13.4 Configuring a Network Connection with YaST

There are many supported networking types on Linux. Most of them use different device names and the configuration files are spread over several locations in the file system. For a detailed overview of the aspects of manual network configuration, see Section 13.6, “Configuring a Network Connection Manually”.

All network interfaces with link up (with a network cable connected) are automatically configured. Additional hardware can be configured any time on the installed system. The following sections describe the network configuration for all types of network connections supported by openSUSE Leap.

13.4.1 Configuring the Network Card with YaST

To configure your Ethernet or Wi-Fi/Bluetooth card in YaST, select System › Network Settings. After starting the module, YaST displays the Network Settings dialog with four tabs: Global Options, Overview, Hostname/DNS and Routing.

The Global Options tab allows you to set general networking options such as the network setup method, IPv6, and general DHCP options. For more information, see Section, “Configuring Global Networking Options”.

The Overview tab contains information about installed network interfaces and configurations. Any properly detected network card is listed with its name. You can manually configure new cards, remove or change their configuration in this dialog. If you want to manually configure a card that was not automatically detected, see Section, “Configuring an Undetected Network Card”. If you want to change the configuration of an already configured card, see Section, “Changing the Configuration of a Network Card”.

The Hostname/DNS tab allows to set the host name of the machine and name the servers to be used. For more information, see Section, “Configuring Host Name and DNS”.

The Routing tab is used for the configuration of routing. See Section, “Configuring Routing” for more information.

Configuring Network Settings
Figure 13.3: Configuring Network Settings Configuring Global Networking Options

The Global Options tab of the YaST Network Settings module allows you to set important global networking options, such as the use of NetworkManager, IPv6 and DHCP client options. These settings are applicable for all network interfaces.

In the Network Setup Method choose the way network connections are managed. If you want a NetworkManager desktop applet to manage connections for all interfaces, choose NetworkManager Service. NetworkManager is well suited for switching between multiple wired and wireless networks. If you do not run a desktop environment, or if your computer is a Xen server, virtual system, or provides network services such as DHCP or DNS in your network, use the Wicked Service method. If NetworkManager is used, nm-applet should be used to configure network options and the Overview, Hostname/DNS and Routing tabs of the Network Settings module are disabled. For more information on NetworkManager, see Chapter 28, Using NetworkManager.

In the IPv6 Protocol Settings choose whether to use the IPv6 protocol. It is possible to use IPv6 together with IPv4. By default, IPv6 is enabled. However, in networks not using IPv6 protocol, response times can be faster with IPv6 protocol disabled. To disable IPv6, deactivate Enable IPv6. If IPv6 is disabled, the Kernel no longer loads the IPv6 module automatically. This setting will be applied after reboot.

In the DHCP Client Options configure options for the DHCP client. The DHCP Client Identifier must be different for each DHCP client on a single network. If left empty, it defaults to the hardware address of the network interface. However, if you are running several virtual machines using the same network interface and, therefore, the same hardware address, specify a unique free-form identifier here.

The Hostname to Send specifies a string used for the host name option field when the DHCP client sends messages to DHCP server. Some DHCP servers update name server zones (forward and reverse records) according to this host name (Dynamic DNS). Also, some DHCP servers require the Hostname to Send option field to contain a specific string in the DHCP messages from clients. Leave AUTO to send the current host name (that is the one defined in /etc/HOSTNAME). Make the option field empty for not sending any host name.

If you do not want to change the default route according to the information from DHCP, deactivate Change Default Route via DHCP. Changing the Configuration of a Network Card

To change the configuration of a network card, select a card from the list of the detected cards in Network Settings › Overview in YaST and click Edit. The Network Card Setup dialog appears in which to adjust the card configuration using the General, Address and Hardware tabs. Configuring IP Addresses

You can set the IP address of the network card or the way its IP address is determined in the Address tab of the Network Card Setup dialog. Both IPv4 and IPv6 addresses are supported. The network card can have No IP Address (which is useful for bonding devices), a Statically Assigned IP Address (IPv4 or IPv6) or a Dynamic Address assigned via DHCP or Zeroconf or both.

If using Dynamic Address, select whether to use DHCP Version 4 Only (for IPv4), DHCP Version 6 Only (for IPv6) or DHCP Both Version 4 and 6.

If possible, the first network card with link that is available during the installation is automatically configured to use automatic address setup via DHCP.

DHCP should also be used if you are using a DSL line but with no static IP assigned by the ISP (Internet Service Provider). If you decide to use DHCP, configure the details in DHCP Client Options in the Global Options tab of the Network Settings dialog of the YaST network card configuration module. If you have a virtual host setup where different hosts communicate through the same interface, an DHCP Client Identifier is necessary to distinguish them.

DHCP is a good choice for client configuration but it is not ideal for server configuration. To set a static IP address, proceed as follows:

  1. Select a card from the list of detected cards in the Overview tab of the YaST network card configuration module and click Edit.

  2. In the Address tab, choose Statically Assigned IP Address.

  3. Enter the IP Address. Both IPv4 and IPv6 addresses can be used. Enter the network mask in Subnet Mask. If the IPv6 address is used, use Subnet Mask for prefix length in format /64.

    Optionally, you can enter a fully qualified Hostname for this address, which will be written to the /etc/hosts configuration file.

  4. Click Next.

  5. To activate the configuration, click OK.

If you use the static address, the name servers and default gateway are not configured automatically. To configure name servers, proceed as described in Section, “Configuring Host Name and DNS”. To configure a gateway, proceed as described in Section, “Configuring Routing”. Configuring Multiple Addresses

One network device can have multiple IP addresses.

Note: Aliases Are a Compatibility Feature

These so-called aliases or labels, respectively, work with IPv4 only. With IPv6 they will be ignored. Using iproute2 network interfaces can have one or more addresses.

Using YaST to set additional addresses for your network card, proceed as follows:

  1. Select a card from the list of detected cards in the Overview tab of the YaST Network Settings dialog and click Edit.

  2. In the Address › Additional Addresses tab, click Add.

  3. Enter IPv4 Address Label, IP Address, and Netmask. Do not include the interface name in the alias name.

  4. To activate the configuration, confirm the settings. Changing the Device Name and Udev Rules

It is possible to change the device name of the network card when it is used. It is also possible to determine whether the network card should be identified by udev via its hardware (MAC) address or via the bus ID. The later option is preferable in large servers to simplify hotplugging of cards. To set these options with YaST, proceed as follows:

  1. Select a card from the list of detected cards in the Overview tab of the YaST Network Settings dialog and click Edit.

  2. Go to the Hardware tab. The current device name is shown in Udev Rules. Click Change.

  3. Select whether udev should identify the card by its MAC Address or Bus ID. The current MAC address and bus ID of the card are shown in the dialog.

  4. To change the device name, check the Change Device Name option and edit the name.

  5. To activate the configuration, confirm the settings. Changing Network Card Kernel Driver

For some network cards, several Kernel drivers may be available. If the card is already configured, YaST allows you to select a Kernel driver to be used from a list of available suitable drivers. It is also possible to specify options for the Kernel driver. To set these options with YaST, proceed as follows:

  1. Select a card from the list of detected cards in the Overview tab of the YaST Network Settings module and click Edit.

  2. Go to the Hardware tab.

  3. Select the Kernel driver to be used in Module Name. Enter any options for the selected driver in Options in the form = =value. If more options are used, they should be space-separated.

  4. To activate the configuration, confirm the settings. Activating the Network Device

If you use the method with wicked, you can configure your device to either start during boot, on cable connection, on card detection, manually, or never. To change device start-up, proceed as follows:

  1. In YaST select a card from the list of detected cards in System › Network Settings and click Edit.

  2. In the General tab, select the desired entry from Device Activation.

    Choose At Boot Time to start the device during the system boot. With On Cable Connection, the interface is watched for any existing physical connection. With On Hotplug, the interface is set when available. It is similar to the At Boot Time option, and only differs in that no error occurs if the interface is not present at boot time. Choose Manually to control the interface manually with ifup. Choose Never to not start the device. The On NFSroot is similar to At Boot Time, but the interface does not shut down with the systemctl stop network command; the network service also cares about the wicked service if wicked is active. Use this if you use an NFS or iSCSI root file system.

  3. To activate the configuration, confirm the settings.

Tip: NFS as a Root File System

On (diskless) systems where the root partition is mounted via network as an NFS share, you need to be careful when configuring the network device with which the NFS share is accessible.

When shutting down or rebooting the system, the default processing order is to turn off network connections, then unmount the root partition. With NFS root, this order causes problems as the root partition cannot be cleanly unmounted as the network connection to the NFS share is already not activated. To prevent the system from deactivating the relevant network device, open the network device configuration tab as described in Section, “Activating the Network Device”, and choose On NFSroot in the Device Activation pane. Setting Up Maximum Transfer Unit Size

You can set a maximum transmission unit (MTU) for the interface. MTU refers to the largest allowed packet size in bytes. A higher MTU brings higher bandwidth efficiency. However, large packets can block up a slow interface for some time, increasing the lag for further packets.

  1. In YaST select a card from the list of detected cards in System › Network Settings and click Edit.

  2. In the General tab, select the desired entry from the Set MTU list.

  3. To activate the configuration, confirm the settings. PCIe Multifunction Devices

Multifunction devices that support LAN, iSCSI, and FCoE are supported. YaST FCoE client (yast2 fcoe-client) shows the private flags in additional columns to allow the user to select the device meant for FCoE. YaST network module (yast2 lan) excludes storage only devices for network configuration. Infiniband Configuration for IP-over-InfiniBand (IPoIB)
  1. In YaST select the InfiniBand device in System › Network Settings and click Edit.

  2. In the General tab, select one of the IP-over-InfiniBand (IPoIB) modes: connected (default) or datagram.

  3. To activate the configuration, confirm the settings.

For more information about InfiniBand, see /usr/src/linux/Documentation/infiniband/ipoib.txt. Configuring the Firewall

Without having to enter the detailed firewall setup as described in Book “Security Guide”, Chapter 15 “Masquerading and Firewalls”, Section 15.4.1 “Configuring the Firewall with YaST”, you can determine the basic firewall setup for your device as part of the device setup. Proceed as follows:

  1. Open the YaST System › Network Settings module. In the Overview tab, select a card from the list of detected cards and click Edit.

  2. Enter the General tab of the Network Settings dialog.

  3. Determine the Firewall Zone to which your interface should be assigned. The following options are available:

    Firewall Disabled

    This option is available only if the firewall is disabled and the firewall does not run. Only use this option if your machine is part of a greater network that is protected by an outer firewall.

    Automatically Assign Zone

    This option is available only if the firewall is enabled. The firewall is running and the interface is automatically assigned to a firewall zone. The zone which contains the keyword any or the external zone will be used for such an interface.

    Internal Zone (Unprotected)

    The firewall is running, but does not enforce any rules to protect this interface. Use this option if your machine is part of a greater network that is protected by an outer firewall. It is also useful for the interfaces connected to the internal network, when the machine has more network interfaces.

    Demilitarized Zone

    A demilitarized zone is an additional line of defense in front of an internal network and the (hostile) Internet. Hosts assigned to this zone can be reached from the internal network and from the Internet, but cannot access the internal network.

    External Zone

    The firewall is running on this interface and fully protects it against other—presumably hostile—network traffic. This is the default option.

  4. To activate the configuration, confirm the settings. Configuring an Undetected Network Card

If a network card is not detected correctly, the card is not included in the list of detected cards. If you are sure that your system includes a driver for your card, you can configure it manually. You can also configure special network device types, such as bridge, bond, TUN or TAP. To configure an undetected network card (or a special device) proceed as follows:

  1. In the System › Network Settings › Overview dialog in YaST click Add.

  2. In the Hardware dialog, set the Device Type of the interface from the available options and Configuration Name. If the network card is a PCMCIA or USB device, activate the respective check box and exit this dialog with Next. Otherwise, you can define the Kernel Module Name to be used for the card and its Options, if necessary.

    In Ethtool Options, you can set ethtool options used by ifup for the interface. For information about available options, see the ethtool manual page.

    If the option string starts with a - (for example, -K interface_name rx on), the second word in the string is replaced with the current interface name. Otherwise (for example, autoneg off speed 10) ifup adds -s interface_name to the beginning.

  3. Click Next.

  4. Configure any needed options, such as the IP address, device activation or firewall zone for the interface in the General, Address, and Hardware tabs. For more information about the configuration options, see Section, “Changing the Configuration of a Network Card”.

  5. If you selected Wireless as the device type of the interface, configure the wireless connection in the next dialog.

  6. To activate the new network configuration, confirm the settings. Configuring Host Name and DNS

If you did not change the network configuration during installation and the Ethernet card was already available, a host name was automatically generated for your computer and DHCP was activated. The same applies to the name service information your host needs to integrate into a network environment. If DHCP is used for network address setup, the list of domain name servers is automatically filled with the appropriate data. If a static setup is preferred, set these values manually.

To change the name of your computer and adjust the name server search list, proceed as follows:

  1. Go to the Network Settings › Hostname/DNS tab in the System module in YaST.

  2. Enter the Hostname and, if needed, the Domain Name. The domain is especially important if the machine is a mail server. Note that the host name is global and applies to all set network interfaces.

    If you are using DHCP to get an IP address, the host name of your computer will be automatically set by the DHCP. You should disable this behavior if you connect to different networks, because they may assign different host names and changing the host name at runtime may confuse the graphical desktop. To disable using DHCP to get an IP address deactivate Change Hostname via DHCP.

    Assign Hostname to Loopback IP associates your host name with (loopback) IP address in /etc/hosts. This is a useful option if you want to have the host name resolvable at all times, even without active network.

  3. In Modify DNS Configuration, select the way the DNS configuration (name servers, search list, the content of the /etc/resolv.conf file) is modified.

    If the Use Default Policy option is selected, the configuration is handled by the netconfig script which merges the data defined statically (with YaST or in the configuration files) with data obtained dynamically (from the DHCP client or NetworkManager). This default policy is usually sufficient.

    If the Only Manually option is selected, netconfig is not allowed to modify the /etc/resolv.conf file. However, this file can be edited manually.

    If the Custom Policy option is selected, a Custom Policy Rule string defining the merge policy should be specified. The string consists of a comma-separated list of interface names to be considered a valid source of settings. Except for complete interface names, basic wild cards to match multiple interfaces are allowed, as well. For example, eth* ppp? will first target all eth and then all ppp0-ppp9 interfaces. There are two special policy values that indicate how to apply the static settings defined in the /etc/sysconfig/network/config file:


    The static settings need to be merged together with the dynamic settings.


    The static settings are used only when no dynamic configuration is available.

    For more information, see the man page of netconfig(8) (man 8 netconfig).

  4. Enter the Name Servers and fill in the Domain Search list. Name servers must be specified by IP addresses, such as, not by host names. Names specified in the Domain Search tab are domain names used for resolving host names without a specified domain. If more than one Domain Search is used, separate domains with commas or white space.

  5. To activate the configuration, confirm the settings.

It is also possible to edit the host name using YaST from the command line. The changes made by YaST take effect immediately (which is not the case when editing the /etc/HOSTNAME file manually). To change the host name, use the following command:

yast dns edit hostname=hostname

To change the name servers, use the following commands:

yast dns edit nameserver1=
yast dns edit nameserver2=
yast dns edit nameserver3= Configuring Routing

To make your machine communicate with other machines and other networks, routing information must be given to make network traffic take the correct path. If DHCP is used, this information is automatically provided. If a static setup is used, this data must be added manually.

  1. In YaST go to Network Settings › Routing.

  2. Enter the IP address of the Default Gateway (IPv4 and IPv6 if necessary). The default gateway matches every possible destination, but if a routing table entry exists that matches the required address, this will be used instead of the default route via the Default Gateway.

  3. More entries can be entered in the Routing Table. Enter the Destination network IP address, Gateway IP address and the Netmask. Select the Device through which the traffic to the defined network will be routed (the minus sign stands for any device). To omit any of these values, use the minus sign -. To enter a default gateway into the table, use default in the Destination field.

    Note: Route Prioritization

    If more default routes are used, it is possible to specify the metric option to determine which route has a higher priority. To specify the metric option, enter - metric number in Options. The route with the highest metric is used as default. If the network device is disconnected, its route will be removed and the next one will be used. However, the current Kernel does not use metric in static routing, only routing daemons like multipathd do.

  4. If the system is a router, enable IPv4 Forwarding and IPv6 Forwarding in the Network Settings as needed.

  5. To activate the configuration, confirm the settings.

13.5 NetworkManager

NetworkManager is the ideal solution for laptops and other portable computers. With NetworkManager, you do not need to worry about configuring network interfaces and switching between networks when you are moving.

13.5.1 NetworkManager and wicked

However, NetworkManager is not a suitable solution for all cases, so you can still choose between the wicked controlled method for managing network connections and NetworkManager. If you want to manage your network connection with NetworkManager, enable NetworkManager in the YaST Network Settings module as described in Section 28.2, “Enabling or Disabling NetworkManager” and configure your network connections with NetworkManager. For a list of use cases and a detailed description of how to configure and use NetworkManager, refer to Chapter 28, Using NetworkManager.

Some differences between wicked and NetworkManager:

root Privileges

If you use NetworkManager for network setup, you can easily switch, stop or start your network connection at any time from within your desktop environment using an applet. NetworkManager also makes it possible to change and configure wireless card connections without requiring root privileges. For this reason, NetworkManager is the ideal solution for a mobile workstation.

wicked also provides some ways to switch, stop or start the connection with or without user intervention, like user-managed devices. However, this always requires root privileges to change or configure a network device. This is often a problem for mobile computing, where it is not possible to preconfigure all the connection possibilities.

Types of Network Connections

Both wicked and NetworkManager can handle network connections with a wireless network (with WEP, WPA-PSK, and WPA-Enterprise access) and wired networks using DHCP and static configuration. They also support connection through dial-up and VPN. With NetworkManager you can also connect a mobile broadband (3G) modem or set up a DSL connection, which is not possible with the traditional configuration.

NetworkManager tries to keep your computer connected at all times using the best connection available. If the network cable is accidentally disconnected, it tries to reconnect. It can find the network with the best signal strength from the list of your wireless connections and automatically use it to connect. To get the same functionality with wicked, more configuration effort is required.

13.5.2 NetworkManager Functionality and Configuration Files

The individual network connection settings created with NetworkManager are stored in configuration profiles. The system connections configured with either NetworkManager or YaST are saved in /etc/networkmanager/system-connections/* or in /etc/sysconfig/network/ifcfg-*. For GNOME, all user-defined connections are stored in GConf.

In case no profile is configured, NetworkManager automatically creates one and names it Auto $INTERFACE-NAME. That is made in an attempt to work without any configuration for as many cases as (securely) possible. If the automatically created profiles do not suit your needs, use the network connection configuration dialogs provided by GNOME to modify them as desired. For more information, see Section 28.3, “Configuring Network Connections”.

13.5.3 Controlling and Locking Down NetworkManager Features

On centrally administered machines, certain NetworkManager features can be controlled or disabled with PolKit, for example if a user is allowed to modify administrator defined connections or if a user is allowed to define his own network configurations. To view or change the respective NetworkManager policies, start the graphical Authorizations tool for PolKit. In the tree on the left side, find them below the network-manager-settings entry. For an introduction to PolKit and details on how to use it, refer to Book “Security Guide”, Chapter 9 “Authorization with PolKit”.

13.6 Configuring a Network Connection Manually

Manual configuration of the network software should be the last alternative. Using YaST is recommended. However, this background information about the network configuration can also assist your work with YaST.

13.6.1 The wicked Network Configuration

The tool and library called wicked provides a new framework for network configuration.

One of the challenges with traditional network interface management is that different layers of network management get jumbled together into one single script, or at most two different scripts, that interact with each other in a not-really-well-defined way, with side effects that are difficult to be aware of, obscure constraints and conventions, etc. Several layers of special hacks for a variety of different scenarios increase the maintenance burden. Address configuration protocols are being used that are implemented via daemons like dhcpcd, which interact rather poorly with the rest of the infrastructure. Funky interface naming schemes that require heavy udev support are introduced to achieve persistent identification of interfaces.

The idea of wicked is to decompose the problem in several ways. None of them is entirely novel, but trying to put ideas from different projects together is hopefully going to create a better solution overall.

One approach is to use a client/server model. This allows wicked to define standardized facilities for things like address configuration that are well integrated with the overall framework. For example, with address configuration, the administrator may request that an interface should be configured via DHCP or IPv4 zeroconf, and all the address configuration service does is obtain the lease from its server, and pass it on to the wicked server process, which installs the requested addresses and routes.

The other approach to decomposing the problem is to enforce the layering aspect. For any type of network interface, it is possible to define a dbus service that configures the network interface's device layer—a VLAN, a bridge, a bonding, or a paravirtualized device. Common functionality, such as address configuration, is implemented by joint services that are layered on top of these device specific services, without having to implement them specifically.

The wicked framework implements these two aspects by using a variety of dbus services, which get attached to a network interface depending on its type. Here is a rough overview of the current object hierarchy in wicked.

Each network interface is represented via a child object of /org/opensuse/Network/Interfaces. The name of the child object is given by its ifindex. For example, the loopback interface, which usually gets ifindex 1, is /org/opensuse/Network/Interfaces/1, the first Ethernet interface registered is /org/opensuse/Network/Interfaces/2.

Each network interface has a class associated with it, which is used to select the dbus interfaces it supports. By default, each network interface is of class netif, and wickedd will automatically attach all interfaces compatible with this class. In the current implementation, this includes the following interfaces:


Generic network interface functions, such as taking the link up or down, assigning an MTU, etc.

org.opensuse.Network.Addrconf.ipv4.dhcp, org.opensuse.Network.Addrconf.ipv6.dhcp,

Address configuration services for DHCP, IPv4 zeroconf, etc.

Beyond this, network interfaces may require or offer special configuration mechanisms. For example, for an Ethernet device, you should be able to control the link speed, offloading of checksumming, etc. To achieve this, Ethernet devices have a class of their own, called netif-ethernet, which is a subclass of netif. As a consequence, the dbus interfaces assigned to an Ethernet interface include all the services listed above, plus org.opensuse.Network.Ethernet, which is a service available only to objects belonging to the netif-ethernet class.

Similarly, there exist classes for interface types like bridges, VLANs, bonds, or infinibands.

How do you interact with an interface that needs to be created first—such as a VLAN, which is really a virtual network interface that sits on top of an Ethernet device. For these, wicked defines factory interfaces, such as org.opensuse.Network.VLAN.Factory. Such a factory interface offers a single function that lets you create an interface of the requested type. These factory interfaces are attached to the /org/opensuse/Network/Interfaces list node. wicked Architecture and Features

The wicked service comprises several parts as depicted in Figure 13.4, “wicked architecture”.

wicked architecture
Figure 13.4: wicked architecture

wicked currently supports the following:

  • Configuration file back-ends to parse SUSE style /etc/sysconfig/network files.

  • An internal configuration back-end to represent network interface configuration in XML.

  • Bring up and shutdown of normal network interfaces such as Ethernet or InfiniBand, VLAN, bridge, bonds, tun, tap, dummy, macvlan, macvtap, hsi, qeth, iucv, and wireless (currently limited to one wpa-psk/eap network) devices.

  • A built-in DHCPv4 client and a built-in DHCPv6 client.

  • The Section, “Nanny” daemon (enabled by default) helps to automatically bring up configured interfaces when the device is available (interface hotplugging) and set up the IP configuration when a link (carrier) is detected.

  • wicked was implemented as a group of DBus services that are integrated with systemd. So the usual systemctl commands will apply to wicked. Using wicked

On SUSE Linux Enterprise, wicked is running by default. In case you want to check what is currently enabled and whether it is running, call:

systemctl status network

If wicked is enabled, you will see something along these lines:

wicked.service - wicked managed network interfaces
    Loaded: loaded (/usr/lib/systemd/system/wicked.service; enabled)

In case something different is running (for example, NetworkManager) and you want to switch to wicked, first stop what is running and then enable wicked:

systemctl is-active network && \
systemctl stop      network
systemctl enable --force wicked

This enables the wicked services, creates the network.service to wicked.service alias link, and starts the network at the next boot.

Starting the server process:

systemctl start wickedd

This starts wickedd (the main server) and associated supplicants:

/usr/lib/wicked/bin/wickedd-auto4 --systemd --foreground
/usr/lib/wicked/bin/wickedd-dhcp4 --systemd --foreground
/usr/lib/wicked/bin/wickedd-dhcp6 --systemd --foreground
/usr/sbin/wickedd --systemd --foreground
/usr/sbin/wickedd-nanny --systemd --foreground

Then bringing up the network:

systemctl start wicked

Alternatively use the network.service alias:

systemctl start network

These commands are using the default or system configuration sources as defined in /etc/wicked/client.xml.

To enable debugging, set WICKED_DEBUG in /etc/sysconfig/network/config, for example:


Or, to omit some:


Use the client utility to display interface information for all interfaces or the interface specified with ifname:

wicked show all
wicked show ifname

In XML output:

wicked show-xml all
wicked show-xml ifname

Bringing up one interface:

wicked ifup eth0
wicked ifup wlan0

Because there is no configuration source specified, the wicked client checks its default sources of configuration defined in /etc/wicked/client.xml:

  1. firmware: iSCSI Boot Firmware Table (iBFT)

  2. compat: ifcfg files—implemented for compatibility

Whatever wicked gets from those sources for a given interface is applied. The intended order of importance is firmware, then compat—this may be changed in the future.

For more information, see the wicked man page. Nanny

Nanny is an event and policy driven daemon that is responsible for asynchronous or unsolicited scenarios such as hotplugging devices. Thus the nanny daemon helps with starting or restarting delayed or temporarily gone devices. Nanny monitors device and link changes, and integrates new devices defined by the current policy set. Nanny continues to set up even if ifup already exited because of specified timeout constraints.

By default, the nanny daemon is active on the system. It is enabled in the /etc/wicked/common.xml configuration file:


This setting causes ifup and ifreload to apply a policy with the effective configuration to the nanny daemon; then, nanny configures wickedd and thus ensures hotplug support. It waits in the background for events or changes (such as new devices or carrier on). Bringing Up Multiple Interfaces

For bonds and bridges, it may make sense to define the entire device topology in one file (ifcfg-bondX), and bring it up in one go. wicked then can bring up the whole configuration if you specify the top level interface names (of the bridge or bond):

wicked ifup br0

This command automatically sets up the bridge and its dependencies in the appropriate order without the need to list the dependencies (ports, etc.) separately.

To bring up multiple interfaces in one command:

wicked ifup bond0 br0 br1 br2

Or also all interfaces:

wicked ifup all Using Tunnels with Wicked

When you need to use tunnels with Wicked, the TUNNEL_DEVICE is utilized for this. It permits to specify an optional device name to bind the tunnel to the device. The tunneled packets will only be routed via this device.

For more information, refer to man 5 ifcfg-tunnel. Handling Incremental Changes

With wicked, there is no need to actually take down an interface to reconfigure it (unless it is required by the Kernel). For example, to add another IP address or route to a statically configured network interface, add the IP address to the interface definition, and do another ifup operation. The server will try hard to update only those settings that have changed. This applies to link-level options such as the device MTU or the MAC address, and network-level settings, such as addresses, routes, or even the address configuration mode (for example, when moving from a static configuration to DHCP).

Things get tricky of course with virtual interfaces combining several real devices such as bridges or bonds. For bonded devices, it is not possible to change certain parameters while the device is up. Doing that will result in an error.

However, what should still work, is the act of adding or removing the child devices of a bond or bridge, or choosing a bond's primary interface. Wicked Extensions: Address Configuration

wicked is designed to be extensible with shell scripts. These extensions can be defined in the config.xml file.

Currently, several classes of extensions are supported:

  • link configuration: these are scripts responsible for setting up a device's link layer according to the configuration provided by the client, and for tearing it down again.

  • address configuration: these are scripts responsible for managing a device's address configuration. Usually address configuration and DHCP are managed by wicked itself, but can be implemented by means of extensions.

  • firewall extension: these scripts can apply firewall rules.

Typically, extensions have a start and a stop command, an optional pid file, and a set of environment variables that get passed to the script.

To illustrate how this is supposed to work, look at a firewall extension defined in etc/server.xml:

<dbus-service interface="org.opensuse.Network.Firewall">
 <action name="firewallUp"   command="/etc/wicked/extensions/firewall up"/>
 <action name="firewallDown" command="/etc/wicked/extensions/firewall down"/>

 <!-- default environment for all calls to this extension script -->
 <putenv name="WICKED_OBJECT_PATH" value="$object-path"/>
 <putenv name="WICKED_INTERFACE_NAME" value="$property:name"/>
 <putenv name="WICKED_INTERFACE_INDEX" value="$property:index"/>

The extension is attached to the <dbus-service> tag and defines commands to execute for the actions of this interface. Further, the declaration can define and initialize environment variables passed to the actions. Wicked Extensions: Configuration Files

You can extend the handling of configuration files with scripts as well. For example, DNS updates from leases are ultimately handled by the extensions/resolver script, with behavior configured in server.xml:

<system-updater name="resolver">
 <action name="backup" command="/etc/wicked/extensions/resolver backup"/>
 <action name="restore" command="/etc/wicked/extensions/resolver restore"/>
 <action name="install" command="/etc/wicked/extensions/resolver install"/>
 <action name="remove" command="/etc/wicked/extensions/resolver remove"/>

When an update arrives in wickedd, the system updater routines parse the lease and call the appropriate commands (backup, install, etc.) in the resolver script. This in turn configures the DNS settings using /sbin/netconfig, or by manually writing /etc/resolv.conf as a fallback.

13.6.2 Configuration Files

This section provides an overview of the network configuration files and explains their purpose and the format used. /etc/wicked/common.xml

The /etc/wicked/common.xml file contains common definitions that should be used by all applications. It is sourced/included by the other configuration files in this directory. Even though you can use this file to, for example, enable debugging across all wicked components, we recommend to use the file /etc/wicked/local.xml for this purpose. After applying maintenance updates you might lose your changes as the /etc/wicked/common.xml might be overwritten. The /etc/wicked/common.xml file includes the /etc/wicked/local.xml in the default installation, thus you typically do not need to modify the /etc/wicked/common.xml.

In case you want to disable nanny by setting the <use-nanny> to false, restart the wickedd.service and then run the following command to apply all configurations and policies:

wicked ifup all
Note: Configuration Files

The wickedd, wicked, or nanny programs try to read /etc/wicked/common.xml if their own configuration files do not exist. /etc/wicked/server.xml

The file /etc/wicked/server.xml is read by the wickedd server process at start-up. The file stores extensions to the /etc/wicked/common.xml. On top of that this file configures handling of a resolver and receiving information from addrconf supplicants, for example DHCP.

We recommend to add changes required to this file into a separate file /etc/wicked/server-local.xml, that gets included by /etc/wicked/server.xml. By using a separate file you avoid overwriting of your changes during maintenance updates. /etc/wicked/client.xml

The /etc/wicked/client.xml is used by the wicked command. The file specifies the location of a script used when discovering devices managed by ibft and also configures locations of network interface configurations.

We recommend to add changes required to this file into a separate file /etc/wicked/client-local.xml, that gets included by /etc/wicked/server.xml. By using a separate file you avoid overwriting of your changes during maintenance updates. /etc/wicked/nanny.xml

The /etc/wicked/nanny.xml configures types of link layers. We recommend to add specific configuration into a separate file: /etc/wicked/nanny-local.xml to avoid losing the changes during maintenance updates. /etc/sysconfig/network/ifcfg-*

These files contain the traditional configurations for network interfaces. In SUSE Linux Enterprise 11, this was the only supported format besides iBFT firmware.

Note: wicked and the ifcfg-* Files

wicked reads these files if you specify the compat: prefix. According to the SUSE Linux Enterprise Server 12 default configuration in /etc/wicked/client.xml, wicked tries these files before the XML configuration files in /etc/wicked/ifconfig.

The --ifconfig switch is provided mostly for testing only. If specified, default configuration sources defined in /etc/wicked/ifconfig are not applied.

The ifcfg-* files include information such as the start mode and the IP address. Possible parameters are described in the manual page of ifup. Additionally, most variables from the dhcp and wireless files can be used in the ifcfg-* files if a general setting should be used for only one interface. However, most of the /etc/sysconfig/network/config variables are global and cannot be overridden in ifcfg-files. For example, NETCONFIG_* variables are global.

For configuring macvlan and macvtab interfaces, see the ifcfg-macvlan and ifcfg-macvtap man pages. For example, for a macvlan interface provide a ifcfg-macvlan0 with settings as follows:


For ifcfg.template, see Section, “/etc/sysconfig/network/config, /etc/sysconfig/network/dhcp, and /etc/sysconfig/network/wireless. /etc/sysconfig/network/config, /etc/sysconfig/network/dhcp, and /etc/sysconfig/network/wireless

The file config contains general settings for the behavior of ifup, ifdown and ifstatus. dhcp contains settings for DHCP and wireless for wireless LAN cards. The variables in all three configuration files are commented. Some variables from /etc/sysconfig/network/config can also be used in ifcfg-* files, where they are given a higher priority. The /etc/sysconfig/network/ifcfg.template file lists variables that can be specified in a per interface scope. However, most of the /etc/sysconfig/network/config variables are global and cannot be overridden in ifcfg-files. For example, NETWORKMANAGER or NETCONFIG_* variables are global.

Note: Using DHCPv6

In SUSE Linux Enterprise 11, DHCPv6 used to work even on networks where IPv6 Router Advertisements (RAs) were not configured properly. Starting with SUSE Linux Enterprise 12, DHCPv6 will correctly require that at least one of the routers on the network sends out RAs that indicate that this network is managed by DHCPv6.

For those networks where the router cannot be configured correctly, there is an ifcfg option that allows the user to override this behavior by specifying DHCLIENT6_MODE='managed' in the ifcfg file. You can also activate this workaround with a boot parameter in the installation system:

ifcfg=eth0=dhcp6,DHCLIENT6_MODE=managed /etc/sysconfig/network/routes and /etc/sysconfig/network/ifroute-*

The static routing of TCP/IP packets is determined by the /etc/sysconfig/network/routes and /etc/sysconfig/network/ifroute-* files. All the static routes required by the various system tasks can be specified in /etc/sysconfig/network/routes: routes to a host, routes to a host via a gateway and routes to a network. For each interface that needs individual routing, define an additional configuration file: /etc/sysconfig/network/ifroute-*. Replace the wild card (*) with the name of the interface. The entries in the routing configuration files look like this:

# Destination     Gateway           Netmask            Interface  Options

The route's destination is in the first column. This column may contain the IP address of a network or host or, in the case of reachable name servers, the fully qualified network or host name. The network should be written in CIDR notation (address with the associated routing prefix-length) such as for IPv4 or fc00::/7 for IPv6 routes. The keyword default indicates that the route is the default gateway in the same address family as the gateway. For devices without a gateway use explicit or ::/0 destinations.

The second column contains the default gateway or a gateway through which a host or network can be accessed.

The third column is deprecated; it used to contain the IPv4 netmask of the destination. For IPv6 routes, the default route, or when using a prefix-length (CIDR notation) in the first column, enter a dash (-) here.

The fourth column contains the name of the interface. If you leave it empty using a dash (-), it can cause unintended behavior in /etc/sysconfig/network/routes. For more information, see the routes man page.

An (optional) fifth column can be used to specify special options. For details, see the routes man page.

Example 13.5: Common Network Interfaces and Some Static Routes
# --- IPv4 routes in CIDR prefix notation:
# Destination     [Gateway]         -                  Interface       -                 -                  lo  -                 -                  eth0
default     -                  eth0     -                  eth1     -                  eth1

# --- IPv4 routes in deprecated netmask notation"
# Destination     [Dummy/Gateway]   Netmask            Interface
#       lo       eth0
default             eth0    eth1        eth1

# --- IPv6 routes are always using CIDR notation:
# Destination     [Gateway]                -           Interface
2001:DB8:100::/64 -                        -           eth0
2001:DB8:100::/32 fe80::216:3eff:fe6d:c042 -           eth0 /etc/resolv.conf

The domain to which the host belongs is specified in /etc/resolv.conf (keyword search). Up to six domains with a total of 256 characters can be specified with the search option. When resolving a name that is not fully qualified, an attempt is made to generate one by attaching the individual search entries. Up to 3 name servers can be specified with the nameserver option, each on a line of its own. Comments are preceded by hash mark or semicolon signs (# or ;). As an example, see Example 13.6, “/etc/resolv.conf.

However, the /etc/resolv.conf should not be edited by hand. Instead, it is generated by the netconfig script. To define static DNS configuration without using YaST, edit the appropriate variables manually in the /etc/sysconfig/network/config file:


list of DNS domain names used for host name lookup


list of name server IP addresses to use for host name lookup


the name of the DNS forwarder that needs to be configured, for example bind or resolver


arbitrary options that will be written to /etc/resolv.conf, for example:

debug attempts:1 timeout:10

For more information, see the resolv.conf man page.


list of up to 10 items, for example:

For more information, see the resolv.conf man page.

To disable DNS configuration using netconfig, set NETCONFIG_DNS_POLICY=''. For more information about netconfig, see the netconfig(8) man page (man 8 netconfig).

Example 13.6: /etc/resolv.conf
# Our domain
# We use ( as nameserver
nameserver /sbin/netconfig

netconfig is a modular tool to manage additional network configuration settings. It merges statically defined settings with settings provided by autoconfiguration mechanisms as DHCP or PPP according to a predefined policy. The required changes are applied to the system by calling the netconfig modules that are responsible for modifying a configuration file and restarting a service or a similar action.

netconfig recognizes three main actions. The netconfig modify and netconfig remove commands are used by daemons such as DHCP or PPP to provide or remove settings to netconfig. Only the netconfig update command is available for the user:


The netconfig modify command modifies the current interface and service specific dynamic settings and updates the network configuration. Netconfig reads settings from standard input or from a file specified with the --lease-file filename option and internally stores them until a system reboot (or the next modify or remove action). Already existing settings for the same interface and service combination are overwritten. The interface is specified by the -i interface_name parameter. The service is specified by the -s service_name parameter.


The netconfig remove command removes the dynamic settings provided by a modificatory action for the specified interface and service combination and updates the network configuration. The interface is specified by the -i interface_name parameter. The service is specified by the -s service_name parameter.


The netconfig update command updates the network configuration using current settings. This is useful when the policy or the static configuration has changed. Use the -m module_type parameter, if you want to update a specified service only (dns, nis, or ntp).

The netconfig policy and the static configuration settings are defined either manually or using YaST in the /etc/sysconfig/network/config file. The dynamic configuration settings provided by autoconfiguration tools such as DHCP or PPP are delivered directly by these tools with the netconfig modify and netconfig remove actions. When NetworkManager is enabled, netconfig (in policy mode auto) uses only NetworkManager settings, ignoring settings from any other interfaces configured using the traditional ifup method. If NetworkManager does not provide any setting, static settings are used as a fallback. A mixed usage of NetworkManager and the wicked method is not supported.

For more information about netconfig, see man 8 netconfig. /etc/hosts

In this file, shown in Example 13.7, “/etc/hosts, IP addresses are assigned to host names. If no name server is implemented, all hosts to which an IP connection will be set up must be listed here. For each host, enter a line consisting of the IP address, the fully qualified host name, and the host name into the file. The IP address must be at the beginning of the line and the entries separated by blanks and tabs. Comments are always preceded by the # sign.

Example 13.7: /etc/hosts localhost jupiter venus /etc/networks

Here, network names are converted to network addresses. The format is similar to that of the hosts file, except the network names precede the addresses. See Example 13.8, “/etc/networks.

Example 13.8: /etc/networks
localnet /etc/host.conf

Name resolution—the translation of host and network names via the resolver library—is controlled by this file. This file is only used for programs linked to libc4 or libc5. For current glibc programs, refer to the settings in /etc/nsswitch.conf. Each parameter must always be entered on a separate line. Comments are preceded by a # sign. Table 13.2, “Parameters for /etc/host.conf” shows the parameters available. A sample /etc/host.conf is shown in Example 13.9, “/etc/host.conf.

Table 13.2: Parameters for /etc/host.conf

order hosts, bind

Specifies in which order the services are accessed for the name resolution. Available arguments are (separated by blank spaces or commas):

hosts: searches the /etc/hosts file

bind: accesses a name server

nis: uses NIS

multi on/off

Defines if a host entered in /etc/hosts can have multiple IP addresses.

nospoof on spoofalert on/off

These parameters influence the name server spoofing but do not exert any influence on the network configuration.

trim domainname

The specified domain name is separated from the host name after host name resolution (as long as the host name includes the domain name). This option is useful only if names from the local domain are in the /etc/hosts file, but should still be recognized with the attached domain names.

Example 13.9: /etc/host.conf
# We have named running
order hosts bind
# Allow multiple address
multi on /etc/nsswitch.conf

The introduction of the GNU C Library 2.0 was accompanied by the introduction of the Name Service Switch (NSS). Refer to the nsswitch.conf(5) man page and The GNU C Library Reference Manual for details.

The order for queries is defined in the file /etc/nsswitch.conf. A sample nsswitch.conf is shown in Example 13.10, “/etc/nsswitch.conf. Comments are preceded by # signs. In this example, the entry under the hosts database means that a request is sent to /etc/hosts (files) via DNS (see Chapter 19, The Domain Name System).

Example 13.10: /etc/nsswitch.conf
passwd:     compat
group:      compat

hosts:      files dns
networks:   files dns

services:   db files
protocols:  db files
rpc:        files
ethers:     files
netmasks:   files
netgroup:   files nis
publickey:  files

bootparams: files
automount:  files nis
aliases:    files nis
shadow:     compat

The databases available over NSS are listed in Table 13.3, “Databases Available via /etc/nsswitch.conf”. The configuration options for NSS databases are listed in Table 13.4, “Configuration Options for NSS Databases.

Table 13.3: Databases Available via /etc/nsswitch.conf


Mail aliases implemented by sendmail; see man 5 aliases.


Ethernet addresses.


List of networks and their subnet masks. Only needed, if you use subnetting.


User groups used by getgrent. See also the man page for group.


Host names and IP addresses, used by gethostbyname and similar functions.


Valid host and user lists in the network for controlling access permissions; see the netgroup(5) man page.


Network names and addresses, used by getnetent.


Public and secret keys for Secure_RPC used by NFS and NIS+.


User passwords, used by getpwent; see the passwd(5) man page.


Network protocols, used by getprotoent; see the protocols(5) man page.


Remote procedure call names and addresses, used by getrpcbyname and similar functions.


Network services, used by getservent.


Shadow passwords of users, used by getspnam; see the shadow(5) man page.

Table 13.4: Configuration Options for NSS Databases


directly access files, for example, /etc/aliases


access via a database

nis, nisplus

NIS, see also Book “Security Guide”, Chapter 3 “Using NIS”


can only be used as an extension for hosts and networks


can only be used as an extension for passwd, shadow and group /etc/nscd.conf

This file is used to configure nscd (name service cache daemon). See the nscd(8) and nscd.conf(5) man pages. By default, the system entries of passwd, groups and hostsare cached by nscd. This is important for the performance of directory services, like NIS and LDAP, because otherwise the network connection needs to be used for every access to names, groups or hosts.

If the caching for passwd is activated, it usually takes about fifteen seconds until a newly added local user is recognized. Reduce this waiting time by restarting nscd with:

systemctl restart nscd /etc/HOSTNAME

/etc/HOSTNAME contains the fully qualified host name (FQHN). The fully qualified host name is the host name with the domain name attached. This file must contain only one line (in which the host name is set). It is read while the machine is booting.

13.6.3 Testing the Configuration

Before you write your configuration to the configuration files, you can test it. To set up a test configuration, use the ip command. To test the connection, use the ping command.

The command ip changes the network configuration directly without saving it in the configuration file. Unless you enter your configuration in the correct configuration files, the changed network configuration is lost on reboot.

Note: ifconfig and route Are Obsolete

The ifconfig and route tools are obsolete. Use ip instead. ifconfig, for example, limits interface names to 9 characters. Configuring a Network Interface with ip

ip is a tool to show and configure network devices, routing, policy routing, and tunnels.

ip is a very complex tool. Its common syntax is ip options object command. You can work with the following objects:


This object represents a network device.


This object represents the IP address of device.


This object represents an ARP or NDISC cache entry.


This object represents the routing table entry.


This object represents a rule in the routing policy database.


This object represents a multicast address.


This object represents a multicast routing cache entry.


This object represents a tunnel over IP.

If no command is given, the default command is used (usually list).

Change the state of a device with the command ip link set device_name  . For example, to deactivate device eth0, enter ip link set eth0 down. To activate it again, use ip link set eth0 up.

After activating a device, you can configure it. To set the IP address, use ip addr add ip_address + dev device_name. For example, to set the address of the interface eth0 to with standard broadcast (option brd), enter ip addr add brd + dev eth0.

To have a working connection, you must also configure the default gateway. To set a gateway for your system, enter ip route add gateway_ip_address. To translate one IP address to another, use nat: ip route add nat ip_address via other_ip_address.

To display all devices, use ip link ls. To display the running interfaces only, use ip link ls up. To print interface statistics for a device, enter ip -s link ls device_name. To view addresses of your devices, enter ip addr. In the output of the ip addr, also find information about MAC addresses of your devices. To show all routes, use ip route show.

For more information about using ip, enter ip help or see the ip(8) man page. The help option is also available for all ip subcommands. If, for example, you need help for ip addr, enter ip addr help. Find the ip manual in /usr/share/doc/packages/iproute2/ip-cref.pdf. Testing a Connection with ping

The ping command is the standard tool for testing whether a TCP/IP connection works. It uses the ICMP protocol to send a small data packet, ECHO_REQUEST datagram, to the destination host, requesting an immediate reply. If this works, ping displays a message to that effect. This indicates that the network link is functioning.

ping does more than only test the function of the connection between two computers: it also provides some basic information about the quality of the connection. In Example 13.11, “Output of the Command ping”, you can see an example of the ping output. The second-to-last line contains information about the number of transmitted packets, packet loss, and total time of ping running.

As the destination, you can use a host name or IP address, for example, ping or ping The program sends packets until you press CtrlC.

If you only need to check the functionality of the connection, you can limit the number of the packets with the -c option. For example to limit ping to three packets, enter ping -c 3

Example 13.11: Output of the Command ping
ping -c 3
PING ( 56(84) bytes of data.
64 bytes from ( icmp_seq=1 ttl=49 time=188 ms
64 bytes from ( icmp_seq=2 ttl=49 time=184 ms
64 bytes from ( icmp_seq=3 ttl=49 time=183 ms
--- ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2007ms
rtt min/avg/max/mdev = 183.417/185.447/188.259/2.052 ms

The default interval between two packets is one second. To change the interval, ping provides the option -i. For example, to increase the ping interval to ten seconds, enter ping -i 10

In a system with multiple network devices, it is sometimes useful to send the ping through a specific interface address. To do so, use the -I option with the name of the selected device, for example, ping -I wlan1

For more options and information about using ping, enter ping -h or see the ping (8) man page.

Tip: Pinging IPv6 Addresses

For IPv6 addresses use the ping6 command. Note, to ping link-local addresses, you must specify the interface with -I. The following command works, if the address is reachable via eth1:

ping6 -I eth1 fe80::117:21ff:feda:a425

13.6.4 Unit Files and Start-Up Scripts

Apart from the configuration files described above, there are also systemd unit files and various scripts that load the network services while the machine is booting. These are started when the system is switched to the target. Some of these unit files and scripts are described in Some Unit Files and Start-Up Scripts for Network Programs. For more information about systemd, see Chapter 10, The systemd Daemon and for more information about the systemd targets, see the man page of systemd.special (man systemd.special).

Some Unit Files and Start-Up Scripts for Network Programs is the systemd target for networking, but its mean depends on the settings provided by the system administrator.

For more information, see is the systemd target for a multiuser system with all required network services.


Starts xinetd. xinetd can be used to make server services available on the system. For example, it can start vsftpd whenever an FTP connection is initiated.


Starts the rpcbind utility that converts RPC program numbers to universal addresses. It is needed for RPC services, such as an NFS server.


Starts the NIS server.


Starts the NIS client.


Starts the NFS server.


Controls the postfix process.

13.7 Basic Router Setup

A router is a networking device that delivers and receives data (network packets) to or from more than one network back and forth. You often use a router to connect your local network to the remote network (Internet) or to connect local network segments. With SUSE Linux Enterprise Server you can build a router with features such as NAT (Network Address Translation) or advanced firewalling.

The following are basic steps to turn SUSE Linux Enterprise Server into a router.

  1. Enable forwarding, for example in /etc/sysctl.d/50-router.conf

    net.ipv4.conf.all.forwarding = 1
    net.ipv6.conf.all.forwarding = 1

    Then provide a static IPv4 and IPv6 IP setup for the interfaces. Enabling forwarding disables several mechanisms, for example IPv6 does not accept an IPv6 RA (router advertisement) anymore, which also prevents the creation of a default route.

  2. In many situations, such as when you can reach the same (internal) network via more than one interface , or when VPN is usually is used (and already on normal multi-home hosts), you must disable the IPv4 reverse path filter (this feature does not currently exist for IPv6):

    net.ipv4.conf.all.rp_filter = 0

    You can also filter with firewall settings instead.

  3. To accept an IPv6 RA (from the router on an external, uplink, or ISP interface) and create a default (or also a more specific) IPv6 route again, set:

    net.ipv6.conf.${ifname}.accept_ra = 2
    net.ipv6.conf.${ifname}.autoconf = 0

    (Note: eth0.42 needs to be written as eth0/42 in a dot-separated sysfs path.)

More router behavior and forwarding dependencies are described in

To provide IPv6 on your internal (DMZ) interfaces, and announce yourself as an IPv6 router and autoconf networks to the clients, install and configure radvd in /etc/radvd.conf, for example:

interface eth0
    IgnoreIfMissing on;         # do not fail if interface missed

    AdvSendAdvert on;           # enable sending RAs
    AdvManagedFlag on;          # IPv6 addresses managed via DHCPv6
    AdvOtherConfigFlag on;      # DNS, NTP... only via DHCPv6

    AdvDefaultLifetime 3600;    # client default route lifetime of 1 hour

    prefix 2001:db8:0:1::/64    # (/64 is default and required for autoconf)
        AdvAutonomous off;         # Disable address autoconf (DHCPv6 only)

        AdvValidLifetime 3600;     # prefix (autoconf addr) is valid 1 h
        AdvPreferredLifetime 1800; # prefix (autoconf addr) is prefered 1/2 h

Lastly configure the firewall. In SuSEfirewall2, you need to set FW_ROUTE="yes" (otherwise it will also reset forwarding sysctl again) and define the interfaces in the FW_DEV_INT, FW_DEV_EXT (and FW_DEV_DMZ) zone variables as needed, perhaps also FW_MASQUERADE="yes" and FW_MASQ_DEV.

13.8 Setting Up Bonding Devices

For some systems, there is a desire to implement network connections that comply to more than the standard data security or availability requirements of a typical Ethernet device. In these cases, several Ethernet devices can be aggregated to a single bonding device.

The configuration of the bonding device is done by means of bonding module options. The behavior is mainly affected by the mode of the bonding device. By default, this is mode=active-backup which means that a different slave device will become active if the active slave fails.

Tip: Bonding and Xen

Using bonding devices is only of interest for machines where you have multiple real network cards available. In most configurations, this means that you should use the bonding configuration only in Dom0. Only if you have multiple network cards assigned to a VM Guest system it may also be useful to set up the bond in a VM Guest.

To configure a bonding device, use the following procedure:

  1. Run YaST › System › Network Settings.

  2. Use Add and change the Device Type to Bond. Proceed with Next.

  3. Select how to assign the IP address to the bonding device. Three methods are at your disposal:

    • No IP Address

    • Dynamic Address (with DHCP or Zeroconf)

    • Statically assigned IP Address

    Use the method that is appropriate for your environment.

  4. In the Bond Slaves tab, select the Ethernet devices that should be included into the bond by activating the related check box.

  5. Edit the Bond Driver Options. The modes that are available for configuration are the following:

    • balance-rr

    • active-backup

    • balance-xor

    • broadcast

    • 802.3ad

      802.3ad is the standardized LACP IEEE 802.3ad Dynamic link aggregation mode.

    • balance-tlb

    • balance-alb

  6. Make sure that the parameter miimon=100 is added to the Bond Driver Options. Without this parameter, the data integrity is not checked regularly.

  7. Click Next and leave YaST with OK to create the device.

All modes, and many more options are explained in detail in the Linux Ethernet Bonding Driver HOWTO found at /usr/src/linux/Documentation/networking/bonding.txt after installing the package kernel-source.

13.8.1 Hotplugging of Bonding Slaves

In specific network environments (such as High Availability), there are cases when you need to replace a bonding slave interface with another one. The reason may be a constantly failing network device. The solution is to set up hotplugging of bonding slaves.

The bond is configured as usual (according to man 5 ifcfg-bonding), for example:

          STARTMODE='auto' # or 'onboot'
          BONDING_MODULE_OPTS='mode=active-backup miimon=100'

The slaves are specified with STARTMODE=hotplug and BOOTPROTO=none:



BOOTPROTO=none uses the ethtool options (when provided), but does not set the link up on ifup eth0. The reason is that the slave interface is controlled by the bond master.

STARTMODE=hotplug causes the slave interface to join the bond automatically when it is available.

The udev rules in /etc/udev/rules.d/70-persistent-net.rules need to be changed to match the device by bus ID (udev KERNELS keyword equal to "SysFS BusID" as visible in hwinfo --netcard) instead of by MAC address to allow to replacement of defective hardware (a network card in the same slot but with a different MAC), and to avoid confusion as the bond changes the MAC address of all its slaves.

For example:

SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*",
KERNELS=="0000:00:19.0", ATTR{dev_id}=="0x0", ATTR{type}=="1",
KERNEL=="eth*", NAME="eth0"

At boot time, the systemd network.service does not wait for the hotplug slaves, but for the bond to become ready, which requires at least one available slave. When one of the slave interfaces gets removed (unbind from NIC driver, rmmod of the NIC driver or true PCI hotplug remove) from the system, the kernel removes it from the bond automatically. When a new card is added to the system (replacement of the hardware in the slot), udev renames it using the bus-based persistent name rule to the name of the slave, and calls ifup for it. The ifup call automatically joins it into the bond.

13.9 Setting Up Team Devices for Network Teaming

The term link aggregation is the general term which describes combining (or aggregating) a network connection to provide a logical layer. Sometimes you find the terms channel teaming, Ethernet bonding, port truncating, etc. which are synonyms and refer to the same concept.

This concept is widely known as bonding and was originally integrated into the Linux kernel (see Section 13.8, “Setting Up Bonding Devices” for the original implementation). The term Network Teaming is used to refer to the new implementation of this concept.

The main difference between bonding and Network Teaming is that teaming supplies a set of small kernel modules which are responsible for providing an interface for teamd instances. Everything else is handled in user space. This is different from the original bonding implementation which contains all of its functionality exclusively in the kernel.

Both implementations, bonding and Network Teaming, can be used in parallel. Network Teaming is an alternative to the existing bonding implementation. It does not replace bonding.

Network Teaming can be used for different use cases. The two most important use cases are explained later and involve:

  • Load balancing between different network devices.

  • Failover from one network device to another in case one of the devices should fail.

Currently, there is no YaST module to support creating a teaming device. You need to configure Network Teaming manually. The general procedure is shown below which can be applied for all your Network Teaming configurations:

Procedure 13.1: General Procedure
  1. Make sure you have all the necessary packages installed. Install the packages libteam-tools , libteamdctl0 , libteamdctl0 , and python-libteam .

  2. Create a configuration file under /etc/sysconfig/network/. Usually it will be ifcfg-team0. If you need more than one Network Teaming device, give them ascending numbers.

    This configuration file contains several variables which are explained in the man pages (see man ifcfg and man ifcfg-team).

  3. Remove the configuration files of the interfaces which will be used for the teaming device (usually ifcfg-eth0 and ifcfg-eth1).

    It is recommended to make a backup and remove both files. Wicked will re-create the configuration files with the necessary parameters for teaming.

  4. Optionally, check if everything is included in Wicked's configuration file:

    wicked show-config
  5. Start the Network Teaming device team0:

    wicked all ifup team0

    In case you need additional debug information, use the option --debug all after the all subcommand.

  6. Check the status of the Network Teaming device. This can be done by the following commands:

    • Get the state of the teamd instance from Wicked:

      wicked ifstatus --verbose team0
    • Get the state of the entire instance:

      teamdctl team0 state
    • Get the systemd state of the teamd instance:

      systemctl status teamd@team0

    Each of them shows a slightly different view depending on your needs.

  7. In case you need to change something in the ifcfg-team0 file afterward, reload its configuration with:

    wicked ifreload team0

Do not use systemctl for starting or stopping the teaming device! Instead, use the wicked command as shown above.

13.9.1 Use Case: Loadbalancing with Network Teaming

Loadbalancing is used to improve bandwidth. Use the following configuration file to create a Network Teaming device with loadbalancing capabilities. Proceed with Procedure 13.1, “General Procedure” to set up the device. Check the output with teamdctl.

Example 13.12: Configuration for Loadbalancing with Network Teaming
BOOTPROTO=static 2
IPADDR6="fd00:deca:fbad:50::1/64" 2

TEAM_RUNNER="loadbalance" 3


TEAM_LW_NAME="ethtool" 5


Controls the start of the teaming device. The value of auto means, the interface will be set up when the network service is available and will be started automatically on every reboot.

In case you need to control the device yourself (and prevent it from starting automatically), set STARTMODE to manual.


Sets a static IP address (here for IPv4 and fd00:deca:fbad:50::1 for IPv6).

If the Network Teaming device should use a dynamic IP address, set BOOTPROTO="dhcp" and remove (or comment) the line with IPADDRESS and IPADDR6.


Sets TEAM_RUNNER to loadbalance to activate the loadbalancing mode.


Specifies one or more devices which should be aggregated to create the Network Teaming device.


Defines a link watcher to monitor the state of subordinate devices. The default value ethtool checks only if the device is up and accessible. This makes this check fast enough. However, it does not check if the device can really send or receive packets.

If you need a higher confidence in the connection, use the arp_ping option. This sends pings to an arbitrary host (configured in the TEAM_LW_ARP_PING_TARGET_HOST variable). Only if the replies are received, the Network Teaming device is considered to be up.


Defines the delay in milliseconds between the link coming up (or down) and the runner being notified.

13.9.2 Use Case: Failover with Network Teaming

Failover is used to ensure high availability of a critical Network Teaming device by involving a parallel backup network device. The backup network device is running all the time and takes over if and when the main device fails.

Use the following configuration file to create a Network Teaming device with failover capabilities. Proceed with Procedure 13.1, “General Procedure” to set up the device. Check the output with teamdctl.

Example 13.13: Configuration for DHCP Network Teaming Device
BOOTPROTO=static 2
IPADDR6="fd00:deca:fbad:50::2/64" 2

TEAM_RUNNER=activebackup 3

TEAM_LW_NAME=ethtool 5


Controls the start of the teaming device. The value of auto means, the interface will be set up when the network service is available and will be started automatically on every reboot.

In case you need to control the device yourself (and prevent it from starting automatically), set STARTMODE to manual.


Sets a static IP address (here for IPv4 and fd00:deca:fbad:50::2 for IPv6).

If the Network Teaming device should use a dynamic IP address, set BOOTPROTO="dhcp" and remove (or comment) the line with IPADDRESS and IPADDR6.


Sets TEAM_RUNNER to activebackup to activate the failover mode.


Specifies one or more devices which should be aggregated to create the Network Teaming device.


Defines a link watcher to monitor the state of subordinate devices. The default value ethtool checks only if the device is up and accessible. This makes this check fast enough. However, it does not check if the device can really send or receive packets.

If you need a higher confidence in the connection, use the arp_ping option. This sends pings to an arbitrary host (configured in the TEAM_LW_ARP_PING_TARGET_HOST variable). Only if the replies are received, the Network Teaming device is considered to be up.


Defines the delay in milliseconds between the link coming up (or down) and the runner being notified.

13.10 Software-Defined Networking with Open vSwitch

Software-defined networking (SDN) means separating the system that controls where traffic is sent (the control plane) from the underlying system that forwards traffic to the selected destination (the data plane, also called the forwarding plane). This means that the functions previously fulfilled by a single, usually inflexible switch can now be separated between a switch (data plane) and its controller (control plane). In this model, the controller is programmable and can be very flexible and adapt quickly to changing network conditions.

Open vSwitch is software that implements a distributed virtual multilayer switch that is compatible with the OpenFlow protocol. OpenFlow allows a controller application to modify the configuration of a switch. OpenFlow is layered onto the TCP protocol and is implemented in a range of hardware and software. A single controller can thus drive multiple, very different switches.

13.10.1 Advantages of Open vSwitch

Software-defined networking with Open vSwitch brings several advantages with it, especially when you used together with virtual machines:

  • Networking states can be identified easily.

  • Networks and their live state can be moved from one host to another.

  • Network dynamics are traceable and external software can be enabled to respond to them.

  • You can apply and manipulate tags in network packets to identify which machine they are coming from or going to and maintain other networking context. Tagging rules can be configured and migrated.

  • Open vSwitch implements the GRE protocol (Generic Routing Encapsulation). This allows you, for example, to connect private VM networks to each other.

  • Open vSwitch can be used on its own, but is designed to integrate with networking hardware and can control hardware switches.

13.10.2 Installing Open vSwitch

  1. Install Open vSwitch and supplementary packages:

    root # zypper install openvswitch openvswitch-switch

    If you plan to use Open vSwitch together with the KVM hypervisor, additionally install tunctl . If you plan to use Open vSwitch together with the Xen hypervisor, additionally install openvswitch-kmp-xen .

  2. Enable the Open vSwitch service:

    root # systemctl enable openvswitch
  3. Either restart the computer or use systemctl to start the Open vSwitch service immediately:

    root # systemctl start openvswitch
  4. To check whether Open vSwitch was activated correctly, use:

    root # systemctl status openvswitch

13.10.3 Overview of Open vSwitch Daemons and Utilities

Open vSwitch consists of several components. Among them are a kernel module and various user space components. The kernel module is used for accelerating the data path, but is not necessary for a minimal Open vSwitch installation. Daemons

The central executables of Open vSwitch are its two daemons. When you start the openvswitch service, you are indirectly starting them.

The main Open vSwitch daemon (ovs-vswitchd) provides the implementation of a switch. The Open vSwitch database daemon (ovsdb-server) serves the database that stores the configuration and state of Open vSwitch. Utilities

Open vSwitch also comes with several utilities that help you work with it. The following list is not exhaustive, but instead describes important commands only.


Create, upgrade, compact, and query Open vSwitch databases. Do transactions on Open vSwitch databases.


Configure a running ovs-vswitchd or ovsdb-server daemon.

ovs-dpctl, ovs-dpctl-top

Create, modify, visualize, and delete data paths. Using this tool can interfere with ovs-vswitchd also performing data path management. Therefore, it is often used for diagnostics only.

ovs-dpctl-top creates a top-like visualization for data paths.


Manage any switches adhering to the OpenFlow protocol. ovs-ofctl is not limited to interacting with Open vSwitch.


Provides a high-level interface to the configuration database. It can be used to query and modify the database. In effect, it shows the status of ovs-vswitchd and can be used to configure it.

13.10.4 Creating a Bridge with Open vSwitch

The following example configuration uses the Wicked network service that is used by default on openSUSE Leap. To learn more about Wicked, see Section 13.6, “Configuring a Network Connection Manually”.

When you have installed and started Open vSwitch, proceed as follows:

  1. To configure a bridge for use by your virtual machine, create a file with content like this:



    Set up the bridge automatically when the network service is started.


    The protocol to use for configuring the IP address.


    Mark the configuration as an Open vSwitch bridge.


    Choose which device/devices should be added to the bridge. To add more devices, append additional lines for each of them to the file:


    The SUFFIX can be any alphanumeric string. However, to avoid overwriting a previous definition, make sure the SUFFIX of each device is unique.

    Save the file in the directory /etc/sysconfig/network under the name ifcfg-br0. Instead of br0, you can use any name you want. However, the file name needs to begin with ifcfg-.

    To learn about further options, refer to the man pages of ifcfg (man 5 ifcfg) and ifcfg-ovs-bridge (man 5 ifcfg-ovs-bridge).

  2. Now start the bridge:

    root # wicked ifup br0

    When Wicked is done, it should output the name of the bridge and next to it the state up.

13.10.5 Using Open vSwitch Directly with KVM

After having created the bridge as described before in Section 13.10.4, “Creating a Bridge with Open vSwitch, you can use Open vSwitch to manage the network access of virtual machines created with KVM/QEMU.

  1. To be able to best use the capabilities of Wicked, make some further changes to the bridge configured before. Open the previously created /etc/sysconfig/network/ifcfg-br0 and append a line for another port device:


    Additionally, set BOOTPROTO to none. The file should now look like this:


    The new port device tap0 will be configured in the next step.

  2. Now add a configuration file for the tap0 device:


    Save the file in the directory /etc/sysconfig/network under the name ifcfg-tap0.

    Tip: Allowing Other Users to Access the Tap Device

    To be able to use this tap device from a virtual machine started as a user who is not root, append:


    To allow access for an entire group, append:

  3. Finally, open the configuration for the device defined as the first OVS_BRIDGE_PORT_DEVICE. If you did not change the name, that should be eth0. Therefore, open /etc/sysconfig/network/ifcfg-eth0 and make sure that the following options are set:


    If the file does not exist yet, create it.

  4. Restart the bridge interface using Wicked:

    root # wicked ifreload br0

    This will also trigger a reload of the newly defined bridge port devices.

  5. To start a virtual machine, use, for example:

    root # qemu-kvm \
    -drive file=/PATH/TO/DISK-IMAGE1 \
    -m 512 -net nic,vlan=0,macaddr=00:11:22:EE:EE:EE \
    -net tap,ifname=tap0,script=no,downscript=no2


    The path to the QEMU disk image you want to start.


    Use the tap device (tap0) created before.

    For further information on the usage of KVM/QEMU, see Book “Virtualization Guide.

13.10.6 Using Open vSwitch with libvirt

After having created the bridge as described before in Section 13.10.4, “Creating a Bridge with Open vSwitch, you can add the bridge to an existing virtual machine managed with libvirt. Since libvirt has some support for Open vSwitch bridges already, you can use the bridge created in Section 13.10.4, “Creating a Bridge with Open vSwitch without further changes to the networking configuration.

  1. Open the domain XML file for the intended virtual machine:

    root # virsh edit VM_NAME

    Replace VM_NAME with the name of the desired virtual machine. This will open your default text editor.

  2. Find the networking section of the document by looking for a section starting with <interface type="..."> and ending in </interface>.

    Replace the existing section with a networking section that looks somewhat like this:

    <interface type='bridge'>
      <source bridge='br0'/>
      <virtualport type='openvswitch'/>
    Important: Compatibility of virsh iface-* and Virtual Machine Manager with Open vSwitch

    At the moment, the Open vSwitch compatibility of libvirt is not exposed through the virsh iface-* tools and Virtual Machine Manager. If you use any of these tools, your configuration can break.

  3. You can now start or restart the virtual machine as usual.

For further information on the usage of libvirt, see Book “Virtualization Guide.

13.10.7 For More Information

The documentation section of the Open vSwitch project Web site

Whitepaper by the Open Networking Foundation about software-defined networking and the OpenFlow protocol

14 UEFI (Unified Extensible Firmware Interface)

UEFI (Unified Extensible Firmware Interface) is the interface between the firmware that comes with the system hardware, all the hardware components of the system, and the operating system.

UEFI is becoming more and more available on PC systems and thus is replacing the traditional PC-BIOS. UEFI, for example, properly supports 64-bit systems and offers secure booting (Secure Boot, firmware version 2.3.1c or better required), which is one of its most important features. Lastly, with UEFI a standard firmware will become available on all x86 platforms.

UEFI additionally offers the following advantages:

  • Booting from large disks (over 2 TiB) with a GUID Partition Table (GPT).

  • CPU-independent architecture and drivers.

  • Flexible pre-OS environment with network capabilities.

  • CSM (Compatibility Support Module) to support booting legacy operating systems via a PC-BIOS-like emulation.

For more information, see The following sections are not meant as a general UEFI overview; these are only hints about how some features are implemented in SUSE Linux Enterprise.

14.1 Secure Boot

In the world of UEFI, securing the bootstrapping process means establishing a chain of trust. The platform is the root of this chain of trust; in the context of SUSE Linux Enterprise, the mainboard and the on-board firmware could be considered the platform. Or, put slightly differently, it is the hardware vendor, and the chain of trust flows from that hardware vendor to the component manufacturers, the OS vendors, etc.

The trust is expressed via public key cryptography. The hardware vendor puts a so-called Platform Key (PK) into the firmware, representing the root of trust. The trust relationship with operating system vendors and others is documented by signing their keys with the Platform Key.

Finally, security is established by requiring that no code will be executed by the firmware unless it has been signed by one of these trusted keys—be it an OS boot loader, some driver located in the flash memory of some PCI Express card or on disk, or be it an update of the firmware itself.

Essentially, to use Secure Boot, you need to have your OS loader signed with a key trusted by the firmware, and you need the OS loader to verify that the kernel it loads can be trusted.

Key Exchange Keys (KEK) can be added to the UEFI key database. This way, you can use other certificates, as long as they are signed with the private part of the PK.

14.1.1 Implementation on openSUSE Leap

Microsoft’s Key Exchange Key (KEK) is installed by default.

Note: GUID Partitioning Table (GPT) Required

The Secure Boot feature is enabled by default on UEFI/x86_64 installations. You can find the Enable Secure Boot Support option in the Boot Code Options tab of the Boot Loader Settings dialog. It supports booting when the secure boot is activated in the firmware, while making it possible to boot when it is deactivated.

Secure Boot Support
Figure 14.1: Secure Boot Support

The Secure Boot feature requires that a GUID Partitioning Table (GPT) replaces the old partitioning with a Master Boot Record (MBR). If YaST detects EFI mode during the installation, it will try to create a GPT partition. UEFI expects to find the EFI programs on a FAT-formatted EFI System Partition (ESP).

Supporting UEFI Secure Boot essentially requires having a boot loader with a digital signature that the firmware recognizes as a trusted key. To be useful for SUSE Linux Enterprise customers, that key is trusted by the firmware a priori, without requiring any manual intervention.

There are two ways of getting there. One is to work with hardware vendors to have them endorse a SUSE key, which SUSE then signs the boot loader with. The other way is to go through Microsoft’s Windows Logo Certification program to have the boot loader certified and have Microsoft recognize the SUSE signing key (that is, have it signed with their KEK). By now, SUSE got the loader signed by UEFI Signing Service (that is Microsoft in this case).

UEFI: Secure Boot Process
Figure 14.2: UEFI: Secure Boot Process

At the implementation layer, SUSE uses the shim loader which is installed by default. It is a smart solution that avoids legal issues, and simplifies the certification and signing step considerably. The shim loader’s job is to load a boot loader such as GRUB 2 and verify it; this boot loader in turn will load kernels signed by a SUSE key only.

There are two types of trusted users:

  • First, those who hold the keys. The Platform Key (PK) allows almost everything. The Key Exchange Key (KEK) allows all a PK can except changing the PK.

  • Second, anyone with physical access to the machine. A user with physical access can reboot the machine, and configure UEFI.

UEFI offers two types of variables to fulfill the needs of those users:

  • The first is the so-called Authenticated Variables, which can be updated from both within the boot process (the so-called Boot Services Environment) and the running OS, but only when the new value of the variable is signed with the same key that the old value of the variable was signed with. And they can only be appended to or changed to a value with a higher serial number.

  • The second is the so-called Boot Services Only Variables. These variables are accessible to any code that runs during the boot process. After the boot process ends and before the OS starts, the boot loader must call the ExitBootServices call. After that, these variables are no longer accessible, and the OS cannot touch them.

The various UEFI key lists are of the first type, as this allows online updating, adding, and blacklisting of keys, drivers, and firmware fingerprints. It is the second type of variable, the Boot Services Only Variable, that helps to implement Secure Boot, in a matter that is both secure and open source friendly, and thus compatible with GPLv3.

SUSE starts with shim—a small and simple EFI boot loader—which was originally developed by Fedora. It is signed by a certificate signed by the SUSE KEK and a Microsoft-issued certificate, based on which KEKs are available in the UEFI key database on the system.

This allows shim to load and execute.

shim then goes on to verify that the boot loader it wants to load is trusted. In a default situation shim will use an independent SUSE certificate embedded in its body. In addition, shim will allow to enroll additional keys, overriding the default SUSE key. In the following, we call them Machine Owner Keys or MOKs for short.

Next the boot loader will verify and then boot the kernel, and the kernel will do the same on the modules.

14.1.2 MOK (Machine Owner Key)

If the user (machine owner) wants to replace any components of the boot process, Machine Owner Keys (MOKs) are to be used. The mokutils tool will help with signing components and managing MOKs.

The enrollment process begins with rebooting the machine and interrupting the boot process (for example, pressing a key) when shim loads. shim will then go into enrollment mode, allowing the user to replace the default SUSE key with keys from a file on the boot partition. If the user chooses to do so, shim will then calculate a hash of that file and put the result in a Boot Services Only variable. This allows shim to detect any change of the file made outside of Boot Services and thus avoid tampering with the list of user-approved MOKs.

All of this happens during boot time—only verified code is executing now. Therefore, only a user present at the console can use the machine owner's set of keys. It cannot be malware or a hacker with remote access to the OS because hackers or malware can only change the file, but not the hash stored in the Boot Services Only variable.

The boot loader, after having been loaded and verified by shim, will call back to shim when it wants to verify the kernel—to avoid duplication of the verification code. Shim will use the same list of MOKs for this and tell the boot loader whether it can load the kernel.

This way, you can install your own kernel or boot loader. It is only necessary to install a new set of keys and authorize them by being physically present during the first reboot. Because MOKs are a list and not just a single MOK, you can make shim trust keys from several vendors, allowing dual- and multi-boot from the boot loader.

14.1.3 Booting a Custom Kernel

The following is based on

Secure Boot does not prevent you from using a self-compiled kernel. You must sign it with your own certificate and make that certificate known to the firmware or MOK.

  1. Create a custom X.509 key and certificate used for signing:

    openssl req -new -x509 -newkey rsa:2048 -keyout key.asc \
      -out cert.pem -nodes -days 666 -subj "/CN=$USER/"

    For more information about creating certificates, see

  2. Package the key and the certificate as a PKCS#12 structure:

    openssl pkcs12 -export -inkey key.asc -in cert.pem \
      -name kernel_cert -out cert.p12
  3. Generate an NSS database for use with pesign:

    certutil -d . -N
  4. Import the key and the certificate contained in PKCS#12 into the NSS database:

    pk12util -d . -i cert.p12
  5. Bless the kernel with the new signature using pesign:

    pesign -n . -c kernel_cert -i arch/x86/boot/bzImage \
      -o vmlinuz.signed -s
  6. List the signatures on the kernel image:

    pesign -n . -S -i vmlinuz.signed

    At that point, you can install the kernel in /boot as usual. Because the kernel now has a custom signature the certificate used for signing needs to be imported into the UEFI firmware or MOK.

  7. Convert the certificate to the DER format for import into the firmware or MOK:

    openssl x509 -in cert.pem -outform der -out cert.der
  8. Copy the certificate to the ESP for easier access:

    sudo cp cert.der /boot/efi/
  9. Use mokutil to launch the MOK list automatically.

      1. Import the certificate to MOK:

        mokutil --root-pw --import cert.der

        The --root-pw option enables usage of the root user directly.

      2. Check the list of certificates that are prepared to be enrolled:

        mokutil --list-new
      3. Reboot the system; shim should launch MokManager. You need to enter the root password to confirm the import of the certificate to the MOK list.

      4. Check if the newly imported key was enrolled:

        mokutil --list-enrolled
      1. Alternatively, this is the procedure if you want to launch MOK manually:


      2. In the GRUB 2 menu press the 'c' key.

      3. Type:

        chainloader $efibootdir/MokManager.efi
      4. Select Enroll key from disk.

      5. Navigate to the cert.der file and press Enter.

      6. Follow the instructions to enroll the key. Normally this should be pressing '0' and then 'y' to confirm.

        Alternatively, the firmware menu may provide ways to add a new key to the Signature Database.

14.1.4 Using Non-Inbox Drivers

There is no support for adding non-inbox drivers (that is, drivers that do not come with openSUSE Leap) during installation with Secure Boot enabled. The signing key used for SolidDriver/PLDP is not trusted by default.

It is possible to install third party drivers during installation with Secure Boot enabled in two different ways. In both cases:

  • Add the needed keys to the firmware database via firmware/system management tools before the installation. This option depends on the specific hardware you are using. Consult your hardware vendor for more information.

  • Use a bootable driver ISO from or your hardware vendor to enroll the needed keys in the MOK list at first boot.

To use the bootable driver ISO to enroll the driver keys to the MOK list, follow these steps:

  1. Burn the ISO image above to an empty CD/DVD medium.

  2. Start the installation using the new CD/DVD medium, having the standard SUSE Linux Enterprise media at hand or a URL to a network installation server.

    If doing a network installation, enter the URL of the network installation source on the boot command line using the install= option.

    If doing installation from optical media, the installer will first boot from the driver kit and then ask to insert the first disk of the SUSE Linux Enterprise product.

  3. An initrd containing updated drivers will be used for installation.

For more information, see

14.1.5 Features and Limitations

When booting in Secure Boot mode, the following features apply:

  • Installation to UEFI default boot loader location, a mechanism to keep or restore the EFI boot entry.

  • Reboot via UEFI.

  • Xen hypervisor will boot with UEFI when there is no legacy BIOS to fall back to.

  • UEFI IPv6 PXE boot support.

  • UEFI videomode support, the kernel can retrieve video mode from UEFI to configure KMS mode with the same parameters.

  • UEFI booting from USB devices is supported.

When booting in Secure Boot mode, the following limitations apply:

  • To ensure that Secure Boot cannot be easily circumvented, some kernel features are disabled when running under Secure Boot.

  • Boot loader, kernel, and kernel modules must be signed.

  • Kexec and Kdump are disabled.

  • Hibernation (suspend on disk) is disabled.

  • Access to /dev/kmem and /dev/mem is not possible, not even as root user.

  • Access to the I/O port is not possible, not even as root user. All X11 graphical drivers must use a kernel driver.

  • PCI BAR access through sysfs is not possible.

  • custom_method in ACPI is not available.

  • debugfs for asus-wmi module is not available.

  • the acpi_rsdp parameter does not have any effect on the kernel.

14.2 For More Information

15 Special System Features


This chapter starts with information about various software packages, the virtual consoles and the keyboard layout. We talk about software components like bash, cron and logrotate, because they were changed or enhanced during the last release cycles. Even if they are small or considered of minor importance, users should change their default behavior, because these components are often closely coupled with the system. The chapter concludes with a section about language and country-specific settings (I18N and L10N).

15.1 Information about Special Software Packages

The programs bash, cron, logrotate, locate, ulimit and free are very important for system administrators and many users. Man pages and info pages are two useful sources of information about commands, but both are not always available. GNU Emacs is a popular and very configurable text editor.

15.1.1 The bash Package and /etc/profile

Bash is the default system shell. When used as a login shell, it reads several initialization files. Bash processes them in the order they appear in this list:

  1. /etc/profile

  2. ~/.profile

  3. /etc/bash.bashrc

  4. ~/.bashrc

Make custom settings in ~/.profile or ~/.bashrc. To ensure the correct processing of these files, it is necessary to copy the basic settings from /etc/skel/.profile or /etc/skel/.bashrc into the home directory of the user. It is recommended to copy the settings from /etc/skel after an update. Execute the following shell commands to prevent the loss of personal adjustments:

mv ~/.bashrc ~/.bashrc.old
cp /etc/skel/.bashrc ~/.bashrc
mv ~/.profile ~/.profile.old
cp /etc/skel/.profile ~/.profile

Then copy personal adjustments back from the *.old files.

15.1.2 The cron Package

If you want to run commands regularly and automatically in the background at predefined times, cron is the tool to use. cron is driven by specially formatted time tables. Some come with the system and users can write their own tables if needed.

The cron tables are located in /var/spool/cron/tabs. /etc/crontab serves as a systemwide cron table. Enter the user name to run the command directly after the time table and before the command. In Example 15.1, “Entry in /etc/crontab”, root is entered. Package-specific tables, located in /etc/cron.d, have the same format. See the cron man page (man cron).

Example 15.1: Entry in /etc/crontab
1-59/5 * * * *   root   test -x /usr/sbin/atrun && /usr/sbin/atrun

You cannot edit /etc/crontab by calling the command crontab -e. This file must be loaded directly into an editor, then modified and saved.

A number of packages install shell scripts to the directories /etc/cron.hourly, /etc/cron.daily, /etc/cron.weekly and /etc/cron.monthly, whose execution is controlled by /usr/lib/cron/run-crons. /usr/lib/cron/run-crons is run every 15 minutes from the main table (/etc/crontab). This guarantees that processes that may have been neglected can be run at the proper time.

To run the hourly, daily or other periodic maintenance scripts at custom times, remove the time stamp files regularly using /etc/crontab entries (see Example 15.2, “/etc/crontab: Remove Time Stamp Files”, which removes the hourly one before every full hour, the daily one once a day at 2:14 a.m., etc.).

Example 15.2: /etc/crontab: Remove Time Stamp Files
59 *  * * *     root  rm -f /var/spool/cron/lastrun/cron.hourly
14 2  * * *     root  rm -f /var/spool/cron/lastrun/cron.daily
29 2  * * 6     root  rm -f /var/spool/cron/lastrun/cron.weekly
44 2  1 * *     root  rm -f /var/spool/cron/lastrun/cron.monthly

Or you can set DAILY_TIME in /etc/sysconfig/cron to the time at which cron.daily should start. The setting of MAX_NOT_RUN ensures that the daily tasks get triggered to run, even if the user did not turn on the computer at the specified DAILY_TIME for a longer time. The maximum value of MAX_NOT_RUN is 14 days.

The daily system maintenance jobs are distributed to various scripts for reasons of clarity. They are contained in the package aaa_base. /etc/cron.daily contains, for example, the components, or

15.1.3 Stopping Cron Status Messages

To avoid the mail-flood caused by cron status messages, the default value of SEND_MAIL_ON_NO_ERROR in /etc/sysconfig/cron is set to "no" for new installations. Even with this setting to "no", cron data output will still be sent to the MAILTO address, as documented in the cron man page.

In the update case it is recommended to set these values according to your needs.

15.1.4 Log Files: Package logrotate

There are several system services (daemons) that, along with the kernel itself, regularly record the system status and specific events onto log files. This way, the administrator can regularly check the status of the system at a certain point in time, recognize errors or faulty functions and troubleshoot them with pinpoint precision. These log files are normally stored in /var/log as specified by FHS and grow on a daily basis. The logrotate package helps control the growth of these files.

Configure logrotate with the file /etc/logrotate.conf. In particular, the include specification primarily configures the additional files to read. Programs that produce log files install individual configuration files in /etc/logrotate.d. For example, such files ship with the packages apache2 (/etc/logrotate.d/apache2) and syslog-service (/etc/logrotate.d/syslog).

Example 15.3: Example for /etc/logrotate.conf
# see "man logrotate" for details
# rotate log files weekly

# keep 4 weeks worth of backlogs
rotate 4

# create new (empty) log files after rotating old ones

# uncomment this if you want your log files compressed

# RPM packages drop log rotation information into this directory
include /etc/logrotate.d

# no packages own lastlog or wtmp - we'll rotate them here
#/var/log/wtmp {
#    monthly
#    create 0664 root utmp
#    rotate 1

# system-specific logs may be also be configured here.

logrotate is controlled through cron and is called daily by /etc/cron.daily/logrotate.

Important: Permissions

The create option reads all settings made by the administrator in /etc/permissions*. Ensure that no conflicts arise from any personal modifications.

15.1.5 The locate Command

locate, a command for quickly finding files, is not included in the standard scope of installed software. If desired, install the package mlocate, the successor of the package findutils-locate. The updatedb process is started automatically every night or about 15 minutes after booting the system.

15.1.6 The ulimit Command

With the ulimit (user limits) command, it is possible to set limits for the use of system resources and to have these displayed. ulimit is especially useful for limiting available memory for applications. With this, an application can be prevented from co-opting too much of the system resources and slowing or even hanging up the operating system.

ulimit can be used with various options. To limit memory usage, use the options listed in Table 15.1, “ulimit: Setting Resources for the User”.

Table 15.1: ulimit: Setting Resources for the User


The maximum resident set size


The maximum amount of virtual memory available to the shell


The maximum size of the stack


The maximum size of core files created


All current limits are reported

Systemwide default entries are set in /etc/profile. Editing this file directly is not recommended, because changes will be overwritten during system upgrades. To customize systemwide profile settings, use /etc/profile.local. Per-user settings should be made in ~USER/.bashrc.

Example 15.4: ulimit: Settings in ~/.bashrc
# Limits maximum resident set size (physical memory):
ulimit -m 98304
# Limits of virtual memory:
ulimit -v 98304

Memory allocations must be specified in KB. For more detailed information, see man bash.

Important: ulimit Support

Not all shells support ulimit directives. PAM (for instance, pam_limits) offers comprehensive adjustment possibilities as an alternative to ulimit.

15.1.7 The free Command

The free command displays the total amount of free and used physical memory and swap space in the system, plus the buffers and cache consumed by the kernel. The concept of available RAM dates back to before the days of unified memory management. The slogan free memory is bad memory applies well to Linux. As a result, Linux has always made the effort to balance out caches without actually allowing free or unused memory.

The kernel does not have direct knowledge of any applications or user data. Instead, it manages applications and user data in a page cache. If memory runs short, parts of it are written to the swap partition or to files, from which they can initially be read with the help of the mmap command (see man mmap).

The kernel also contains other caches, such as the slab cache, where the caches used for network access are stored. This may explain the differences between the counters in /proc/meminfo. Most, but not all, of them can be accessed via /proc/slabinfo.

However, if your goal is to find out how much RAM is currently being used, find this information in /proc/meminfo.

15.1.8 Man Pages and Info Pages

For some GNU applications (such as tar), the man pages are no longer maintained. For these commands, use the --help option to get a quick overview of the info pages, which provide more in-depth instructions. Info is GNU's hypertext system. Read an introduction to this system by entering info info. Info pages can be viewed with Emacs by entering emacs -f info or directly in a console with info. You can also use tkinfo, xinfo or the help system to view info pages.

15.1.9 Selecting Man Pages Using the man Command

To read a man page enter man man_page. If a man page with the same name exists in different sections, they will all be listed with the corresponding section numbers. Select the one to display. If you do not enter a section number within a few seconds, the first man page will be displayed.

If you want to change this to the default system behavior, set MAN_POSIXLY_CORRECT=1 in a shell initialization file such as ~/.bashrc.

15.1.10 Settings for GNU Emacs

GNU Emacs is a complex work environment. The following sections cover the configuration files processed when GNU Emacs is started. More information is available at

On start-up, Emacs reads several files containing the settings of the user, system administrator and distributor for customization or preconfiguration. The initialization file ~/.emacs is installed to the home directories of the individual users from /etc/skel. .emacs, in turn, reads the file /etc/skel/.gnu-emacs. To customize the program, copy .gnu-emacs to the home directory (with cp /etc/skel/.gnu-emacs ~/.gnu-emacs) and make the desired settings there.

.gnu-emacs defines the file ~/.gnu-emacs-custom as custom-file. If users make settings with the customize options in Emacs, the settings are saved to ~/.gnu-emacs-custom.

With openSUSE Leap, the emacs package installs the file site-start.el in the directory /usr/share/emacs/site-lisp. The file site-start.el is loaded before the initialization file ~/.emacs. Among other things, site-start.el ensures that special configuration files distributed with Emacs add-on packages, such as psgml, are loaded automatically. Configuration files of this type are located in /usr/share/emacs/site-lisp, too, and always begin with suse-start-. The local system administrator can specify systemwide settings in default.el.

More information about these files is available in the Emacs info file under Init File: info:/emacs/InitFile. Information about how to disable the loading of these files (if necessary) is also provided at this location.

The components of Emacs are divided into several packages:

  • The base package emacs.

  • emacs-x11 (usually installed): the program with X11 support.

  • emacs-nox: the program without X11 support.

  • emacs-info: online documentation in info format.

  • emacs-el: the uncompiled library files in Emacs Lisp. These are not required at runtime.

  • Numerous add-on packages can be installed if needed: emacs-auctex (LaTeX), psgml (SGML and XML), gnuserv (client and server operation) and others.

15.2 Virtual Consoles

Linux is a multiuser and multitasking system. The advantages of these features can be appreciated even on a stand-alone PC system. In text mode, there are six virtual consoles available. Switch between them using AltF1 through AltF6. The seventh console is reserved for X and the tenth console shows kernel messages.

To switch to a console from X without shutting it down, use CtrlAltF1 to CtrlAltF6. To return to X, press AltF7.

15.3 Keyboard Mapping

To standardize the keyboard mapping of programs, changes were made to the following files:


These changes only affect applications that use terminfo entries or whose configuration files are changed directly (vi, emacs, etc.). Applications not shipped with the system should be adapted to these defaults.

Under X, the compose key (multikey) can be enabled as explained in /etc/X11/Xmodmap.

Further settings are possible using the X Keyboard Extension (XKB). This extension is also used by the desktop environment GNOME (gswitchit).

Tip: For More Information

Information about XKB is available in the documents listed in /usr/share/doc/packages/xkeyboard-config (part of the xkeyboard-config package).

15.4 Language and Country-Specific Settings

The system is, to a very large extent, internationalized and can be modified for local needs. Internationalization (I18N) allows specific localization (L10N). The abbreviations I18N and L10N are derived from the first and last letters of the words and, in between, the number of letters omitted.

Settings are made with LC_ variables defined in the file /etc/sysconfig/language. This refers not only to native language support, but also to the categories Messages (Language), Character Set, Sort Order, Time and Date, Numbers and Money. Each of these categories can be defined directly with its own variable or indirectly with a master variable in the file language (see the locale man page).


These variables are passed to the shell without the RC_ prefix and represent the listed categories. The shell profiles concerned are listed below. The current setting can be shown with the command locale.


This variable, if set, overwrites the values of the variables already mentioned.


If none of the previous variables are set, this is the fallback. By default, only RC_LANG is set. This makes it easier for users to enter their own values.


A yes or no variable. If set to no, root always works in the POSIX environment.

The variables can be set with the YaST sysconfig editor. The value of such a variable contains the language code, country code, encoding and modifier. The individual components are connected by special characters:


15.4.1 Some Examples

You should always set the language and country codes together. Language settings follow the standard ISO 639 available at and Country codes are listed in ISO 3166, see

It only makes sense to set values for which usable description files can be found in /usr/lib/locale. Additional description files can be created from the files in /usr/share/i18n using the command localedef. The description files are part of the glibc-i18ndata package. A description file for en_US.UTF-8 (for English and United States) can be created with:

localedef -i en_US -f UTF-8 en_US.UTF-8

This is the default setting if American English is selected during installation. If you selected another language, that language is enabled but still with UTF-8 as the character encoding.


This sets the language to English, country to United States and the character set to ISO-8859-1. This character set does not support the Euro sign, but it can be useful sometimes for programs that have not been updated to support UTF-8. The string defining the charset (ISO-8859-1 in this case) is then evaluated by programs like Emacs.


The above example explicitly includes the Euro sign in a language setting. This setting is obsolete now, as UTF-8 also covers the Euro symbol. It is only useful if an application supports ISO-8859-15 and not UTF-8.

Changes to /etc/sysconfig/language are activated by the following process chain:

  • For the Bash: /etc/profile reads /etc/profile.d/ which, in turn, analyzes /etc/sysconfig/language.

  • For tcsh: At login, /etc/csh.login reads /etc/profile.d/lang.csh which, in turn, analyzes /etc/sysconfig/language.

This ensures that any changes to /etc/sysconfig/language are available at the next login to the respective shell, without having to manually activate them.

Users can override the system defaults by editing their ~/.bashrc accordingly. For instance, if you do not want to use the system-wide en_US for program messages, include LC_MESSAGES=es_ES so that messages are displayed in Spanish instead.

15.4.2 Locale Settings in ~/.i18n

If you are not satisfied with locale system defaults, change the settings in ~/.i18n according to the Bash scripting syntax. Entries in ~/.i18n override system defaults from /etc/sysconfig/language. Use the same variable names but without the RC_ name space prefixes. For example, use LANG instead of RC_LANG:


15.4.3 Settings for Language Support

Files in the category Messages are, as a rule, only stored in the corresponding language directory (like en) to have a fallback. If you set LANG to en_US and the message file in /usr/share/locale/en_US/LC_MESSAGES does not exist, it falls back to /usr/share/locale/en/LC_MESSAGES.

A fallback chain can also be defined, for example, for Breton to French or for Galician to Spanish to Portuguese:



If desired, use the Norwegian variants Nynorsk and Bokmål instead (with additional fallback to no):






Note that in Norwegian, LC_TIME is also treated differently.

One problem that can arise is a separator used to delimit groups of digits not being recognized properly. This occurs if LANG is set to only a two-letter language code like de, but the definition file glibc uses is located in /usr/share/lib/de_DE/LC_NUMERIC. Thus LC_NUMERIC must be set to de_DE to make the separator definition visible to the system.

15.4.4 For More Information

  • The GNU C Library Reference Manual, Chapter Locales and Internationalization. It is included in glibc-info. The package is available from the SUSE Linux Enterprise SDK. The SDK is a module for SUSE Linux Enterprise and is available via an online channel from the SUSE Customer Center. Alternatively, go to, search for SUSE Linux Enterprise Software Development Kit and download it from there. Refer to Book “Start-Up”, Chapter 10 “Installing Add-On Products” for details.

  • Markus Kuhn, UTF-8 and Unicode FAQ for Unix/Linux, currently at

  • Unicode-HOWTO by Bruno Haible, available at

16 Dynamic Kernel Device Management with udev

The kernel can add or remove almost any device in a running system. Changes in the device state (whether a device is plugged in or removed) need to be propagated to user space. Devices need to be configured as soon as they are plugged in and recognized. Users of a certain device need to be informed about any changes in this device's recognized state. udev provides the needed infrastructure to dynamically maintain the device node files and symbolic links in the /dev directory. udev rules provide a way to plug external tools into the kernel device event processing. This enables you to customize udev device handling by, for example, adding certain scripts to execute as part of kernel device handling, or request and import additional data to evaluate during device handling.

16.1 The /dev Directory

The device nodes in the /dev directory provide access to the corresponding kernel devices. With udev, the /dev directory reflects the current state of the kernel. Every kernel device has one corresponding device file. If a device is disconnected from the system, the device node is removed.

The content of the /dev directory is kept on a temporary file system and all files are rendered at every system start-up. Manually created or modified files do not, by design, survive a reboot. Static files and directories that should always be in the /dev directory regardless of the state of the corresponding kernel device can be created with systemd-tmpfiles. The configuration files are found in /usr/lib/tmpfiles.d/ and /etc/tmpfiles.d/; for more information, see the systemd-tmpfiles(8) man page.

16.2 Kernel uevents and udev

The required device information is exported by the sysfs file system. For every device the kernel has detected and initialized, a directory with the device name is created. It contains attribute files with device-specific properties.

Every time a device is added or removed, the kernel sends a uevent to notify udev of the change. The udev daemon reads and parses all provided rules from the /etc/udev/rules.d/*.rules files once at start-up and keeps them in memory. If rules files are changed, added or removed, the daemon can reload the in-memory representation of all rules with the command udevadm control reload_rules. For more details on udev rules and their syntax, refer to Section 16.6, “Influencing Kernel Device Event Handling with udev Rules”.

Every received event is matched against the set of provides rules. The rules can add or change event environment keys, request a specific name for the device node to create, add symbolic links pointing to the node or add programs to run after the device node is created. The driver core uevents are received from a kernel netlink socket.

16.3 Drivers, Kernel Modules and Devices

The kernel bus drivers probe for devices. For every detected device, the kernel creates an internal device structure while the driver core sends a uevent to the udev daemon. Bus devices identify themselves by a specially-formatted ID, which tells what kind of device it is. Usually these IDs consist of vendor and product ID and other subsystem-specific values. Every bus has its own scheme for these IDs, called MODALIAS. The kernel takes the device information, composes a MODALIAS ID string from it and sends that string along with the event. For a USB mouse, it looks like this:


Every device driver carries a list of known aliases for devices it can handle. The list is contained in the kernel module file itself. The program depmod reads the ID lists and creates the file modules.alias in the kernel's /lib/modules directory for all currently available modules. With this infrastructure, module loading is as easy as calling modprobe for every event that carries a MODALIAS key. If modprobe $MODALIAS is called, it matches the device alias composed for the device with the aliases provided by the modules. If a matching entry is found, that module is loaded. All this is automatically triggered by udev.

16.4 Booting and Initial Device Setup

All device events happening during the boot process before the udev daemon is running are lost, because the infrastructure to handle these events resides on the root file system and is not available at that time. To cover that loss, the kernel provides a uevent file located in the device directory of every device in the sysfs file system. By writing add to that file, the kernel resends the same event as the one lost during boot. A simple loop over all uevent files in /sys triggers all events again to create the device nodes and perform device setup.

As an example, a USB mouse present during boot may not be initialized by the early boot logic, because the driver is not available at that time. The event for the device discovery was lost and failed to find a kernel module for the device. Instead of manually searching for possibly connected devices, udev requests all device events from the kernel after the root file system is available, so the event for the USB mouse device runs again. Now it finds the kernel module on the mounted root file system and the USB mouse can be initialized.

From user space, there is no visible difference between a device coldplug sequence and a device discovery during runtime. In both cases, the same rules are used to match and the same configured programs are run.

16.5 Monitoring the Running udev Daemon

The program udevadm monitor can be used to visualize the driver core events and the timing of the udev event processes.

UEVENT[1185238505.276660] add   /devices/pci0000:00/0000:00:1d.2/usb3/3-1 (usb)
UDEV  [1185238505.279198] add   /devices/pci0000:00/0000:00:1d.2/usb3/3-1 (usb)
UEVENT[1185238505.279527] add   /devices/pci0000:00/0000:00:1d.2/usb3/3-1/3-1:1.0 (usb)
UDEV  [1185238505.285573] add   /devices/pci0000:00/0000:00:1d.2/usb3/3-1/3-1:1.0 (usb)
UEVENT[1185238505.298878] add   /devices/pci0000:00/0000:00:1d.2/usb3/3-1/3-1:1.0/input/input10 (input)
UDEV  [1185238505.305026] add   /devices/pci0000:00/0000:00:1d.2/usb3/3-1/3-1:1.0/input/input10 (input)
UEVENT[1185238505.305442] add   /devices/pci0000:00/0000:00:1d.2/usb3/3-1/3-1:1.0/input/input10/mouse2 (input)
UEVENT[1185238505.306440] add   /devices/pci0000:00/0000:00:1d.2/usb3/3-1/3-1:1.0/input/input10/event4 (input)
UDEV  [1185238505.325384] add   /devices/pci0000:00/0000:00:1d.2/usb3/3-1/3-1:1.0/input/input10/event4 (input)
UDEV  [1185238505.342257] add   /devices/pci0000:00/0000:00:1d.2/usb3/3-1/3-1:1.0/input/input10/mouse2 (input)

The UEVENT lines show the events the kernel has sent over netlink. The UDEV lines show the finished udev event handlers. The timing is printed in microseconds. The time between UEVENT and UDEV is the time udev took to process this event or the udev daemon has delayed its execution to synchronize this event with related and already running events. For example, events for hard disk partitions always wait for the main disk device event to finish, because the partition events may rely on the data that the main disk event has queried from the hardware.

udevadm monitor --env shows the complete event environment:

NAME="Logitech USB-PS/2 Optical Mouse"
KEY=70000 0 0 0 0

udev also sends messages to syslog. The default syslog priority that controls which messages are sent to syslog is specified in the udev configuration file /etc/udev/udev.conf. The log priority of the running daemon can be changed with udevadm control log_priority= level/number.

16.6 Influencing Kernel Device Event Handling with udev Rules

A udev rule can match any property the kernel adds to the event itself or any information that the kernel exports to sysfs. The rule can also request additional information from external programs. Every event is matched against all provided rules. All rules are located in the /etc/udev/rules.d directory.

Every line in the rules file contains at least one key value pair. There are two kinds of keys, match and assignment keys. If all match keys match their values, the rule is applied and the assignment keys are assigned the specified value. A matching rule may specify the name of the device node, add symbolic links pointing to the node or run a specified program as part of the event handling. If no matching rule is found, the default device node name is used to create the device node. Detailed information about the rule syntax and the provided keys to match or import data are described in the udev man page. The following example rules provide a basic introduction to udev rule syntax. The example rules are all taken from the udev default rule set that is located under /etc/udev/rules.d/50-udev-default.rules.

Example 16.1: Example udev Rules
# console
KERNEL=="console", MODE="0600", OPTIONS="last_rule"

# serial devices
KERNEL=="ttyUSB*", ATTRS{product}=="[Pp]alm*Handheld*", SYMLINK+="pilot"

# printer
SUBSYSTEM=="usb", KERNEL=="lp*", NAME="usb/%k", SYMLINK+="usb%k", GROUP="lp"

# kernel firmware loader
SUBSYSTEM=="firmware", ACTION=="add", RUN+=""

The console rule consists of three keys: one match key (KERNEL) and two assign keys (MODE, OPTIONS). The KERNEL match rule searches the device list for any items of the type console. Only exact matches are valid and trigger this rule to be executed. The MODE key assigns special permissions to the device node, in this case, read and write permissions to the owner of this device only. The OPTIONS key makes this rule the last rule to be applied to any device of this type. Any later rule matching this particular device type does not have any effect.

The serial devices rule is not available in 50-udev-default.rules anymore, but it is still worth considering. It consists of two match keys (KERNEL and ATTRS) and one assign key (SYMLINK). The KERNEL key searches for all devices of the ttyUSB type. Using the * wild card, this key matches several of these devices. The second match key, ATTRS, checks whether the product attribute file in sysfs for any ttyUSB device contains a certain string. The assign key (SYMLINK) triggers the addition of a symbolic link to this device under /dev/pilot. The operator used in this key (+=) tells udev to additionally perform this action, even if previous or later rules add other symbolic links. As this rule contains two match keys, it is only applied if both conditions are met.

The printer rule deals with USB printers and contains two match keys which must both apply to get the entire rule applied (SUBSYSTEM and KERNEL). Three assign keys deal with the naming for this device type (NAME), the creation of symbolic device links (SYMLINK) and the group membership for this device type (GROUP). Using the * wild card in the KERNEL key makes it match several lp printer devices. Substitutions are used in both, the NAME and the SYMLINK keys to extend these strings by the internal device name. For example, the symbolic link to the first lp USB printer would read /dev/usblp0.

The kernel firmware loader rule makes udev load additional firmware by an external helper script during runtime. The SUBSYSTEM match key searches for the firmware subsystem. The ACTION key checks whether any device belonging to the firmware subsystem has been added. The RUN+= key triggers the execution of the script to locate the firmware that is to be loaded.

Some general characteristics are common to all rules:

  • Each rule consists of one or more key value pairs separated by a comma.

  • A key's operation is determined by the operator. udev rules support several different operators.

  • Each given value must be enclosed by quotation marks.

  • Each line of the rules file represents one rule. If a rule is longer than one line, use \ to join the different lines as you would do in shell syntax.

  • udev rules support a shell-style pattern that matches the *, ?, and [] patterns.

  • udev rules support substitutions.

16.6.1 Using Operators in udev Rules

Creating keys you can choose from several operators, depending on the type of key you want to create. Match keys will normally be used to find a value that either matches or explicitly mismatches the search value. Match keys contain either of the following operators:


Compare for equality. If the key contains a search pattern, all results matching this pattern are valid.


Compare for non-equality. If the key contains a search pattern, all results matching this pattern are valid.

Any of the following operators can be used with assign keys:


Assign a value to a key. If the key previously consisted of a list of values, the key resets and only the single value is assigned.


Add a value to a key that contains a list of entries.


Assign a final value. Disallow any later change by later rules.

16.6.2 Using Substitutions in udev Rules

udev rules support the use of placeholders and substitutions. Use them in a similar fashion as you would do in any other scripts. The following substitutions can be used with udev rules:

%r, $root

The device directory, /dev by default.

%p, $devpath

The value of DEVPATH.

%k, $kernel

The value of KERNEL or the internal device name.

%n, $number

The device number.

%N, $tempnode

The temporary name of the device file.

%M, $major

The major number of the device.

%m, $minor

The minor number of the device.

%s{attribute}, $attr{attribute}

The value of a sysfs attribute (specified by attribute).

%E{variable}, $attr{variable}

The value of an environment variable (specified by variable).

%c, $result

The output of PROGRAM.


The % character.


The $ character.

16.6.3 Using udev Match Keys

Match keys describe conditions that must be met before a udev rule can be applied. The following match keys are available:


The name of the event action, for example, add or remove when adding or removing a device.


The device path of the event device, for example, DEVPATH=/bus/pci/drivers/ipw3945 to search for all events related to the ipw3945 driver.


The internal (kernel) name of the event device.


The subsystem of the event device, for example, SUBSYSTEM=usb for all events related to USB devices.


sysfs attributes of the event device. To match a string contained in the vendor attribute file name, you could use ATTR{vendor}=="On[sS]tream", for example.


Let udev search the device path upwards for a matching device name.


Let udev search the device path upwards for a matching device subsystem name.


Let udev search the device path upwards for a matching device driver name.


Let udev search the device path upwards for a device with matching sysfs attribute values.


The value of an environment variable, for example, ENV{ID_BUS}="ieee1394 to search for all events related to the FireWire bus ID.


Let udev execute an external program. To be successful, the program must return with exit code zero. The program's output, printed to STDOUT, is available to the RESULT key.


Match the output string of the last PROGRAM call. Either include this key in the same rule as the PROGRAM key or in a later one.

16.6.4 Using udev Assign Keys

In contrast to the match keys described above, assign keys do not describe conditions that must be met. They assign values, names and actions to the device nodes maintained by udev.


The name of the device node to be created. After a rule has set a node name, all other rules with a NAME key for this node are ignored.


The name of a symbolic link related to the node to be created. Multiple matching rules can add symbolic links to be created with the device node. You can also specify multiple symbolic links for one node in one rule using the space character to separate the symbolic link names.


The permissions for the new device node. Values specified here overwrite anything that has been compiled in.


Specify a value to be written to a sysfs attribute of the event device. If the == operator is used, this key is also used to match against the value of a sysfs attribute.


Tell udev to export a variable to the environment. If the == operator is used, this key is also used to match against an environment variable.


Tell udev to add a program to the list of programs to be executed for this device. Keep in mind to restrict this to very short tasks to avoid blocking further events for this device.


Add a label where a GOTO can jump to.


Tell udev to skip a number of rules and continue with the one that carries the label referenced by the GOTO key.


Load variables into the event environment such as the output of an external program. udev imports variables of several types. If no type is specified, udev tries to determine the type itself based on the executable bit of the file permissions.

  • program tells udev to execute an external program and import its output.

  • file tells udev to import a text file.

  • parent tells udev to import the stored keys from the parent device.


Tells udev to wait for the specified sysfs file to be created for a certain device. For example, WAIT_FOR_SYSFS="ioerr_cnt" informs udev to wait until the ioerr_cnt file has been created.


The OPTION key may have several values:

  • last_rule tells udev to ignore all later rules.

  • ignore_device tells udev to ignore this event completely.

  • ignore_remove tells udev to ignore all later remove events for the device.

  • all_partitions tells udev to create device nodes for all available partitions on a block device.

16.7 Persistent Device Naming

The dynamic device directory and the udev rules infrastructure make it possible to provide stable names for all disk devices—regardless of their order of recognition or the connection used for the device. Every appropriate block device the kernel creates is examined by tools with special knowledge about certain buses, drive types or file systems. Along with the dynamic kernel-provided device node name, udev maintains classes of persistent symbolic links pointing to the device:

|-- by-id
|   |-- scsi-SATA_HTS726060M9AT00_MRH453M4HWHG7B -> ../../sda
|   |-- scsi-SATA_HTS726060M9AT00_MRH453M4HWHG7B-part1 -> ../../sda1
|   |-- scsi-SATA_HTS726060M9AT00_MRH453M4HWHG7B-part6 -> ../../sda6
|   |-- scsi-SATA_HTS726060M9AT00_MRH453M4HWHG7B-part7 -> ../../sda7
|   |-- usb-Generic_STORAGE_DEVICE_02773 -> ../../sdd
|   `-- usb-Generic_STORAGE_DEVICE_02773-part1 -> ../../sdd1
|-- by-label
|   |-- Photos -> ../../sdd1
|   |-- SUSE10 -> ../../sda7
|   `-- devel -> ../../sda6
|-- by-path
|   |-- pci-0000:00:1f.2-scsi-0:0:0:0 -> ../../sda
|   |-- pci-0000:00:1f.2-scsi-0:0:0:0-part1 -> ../../sda1
|   |-- pci-0000:00:1f.2-scsi-0:0:0:0-part6 -> ../../sda6
|   |-- pci-0000:00:1f.2-scsi-0:0:0:0-part7 -> ../../sda7
|   |-- pci-0000:00:1f.2-scsi-1:0:0:0 -> ../../sr0
|   |-- usb-02773:0:0:2 -> ../../sdd
|   |-- usb-02773:0:0:2-part1 -> ../../sdd1
`-- by-uuid
    |-- 159a47a4-e6e6-40be-a757-a629991479ae -> ../../sda7
    |-- 3e999973-00c9-4917-9442-b7633bd95b9e -> ../../sda6
    `-- 4210-8F8C -> ../../sdd1

16.8 Files used by udev


Virtual file system provided by the Linux kernel, exporting all currently known devices. This information is used by udev to create device nodes in /dev


Dynamically created device nodes and static content created with systemd-tmpfiles; for more information, see the systemd-tmpfiles(8) man page.

The following files and directories contain the crucial elements of the udev infrastructure:


Main udev configuration file.


udev event matching rules.

/usr/lib/tmpfiles.d/ and /etc/tmpfiles.d/

Responsible for static /dev content.


Helper programs called from udev rules.

16.9 For More Information

For more information about the udev infrastructure, refer to the following man pages:


General information about udev, keys, rules and other important configuration issues.


udevadm can be used to control the runtime behavior of udev, request kernel events, manage the event queue and provide simple debugging mechanisms.


Information about the udev event managing daemon.

Part III Services

17 SLP

Configuring a network client requires detailed knowledge about services provided over the network (such as printing or LDAP, for example). To make it easier to configure such services on a network client, the service location protocol (SLP) was developed. SLP makes the availability and configuration data of selected services known to all clients in the local network. Applications that support SLP can use this information to be configured automatically.

18 Time Synchronization with NTP

The NTP (network time protocol) mechanism is a protocol for synchronizing the system time over the network. First, a machine can obtain the time from a server that is a reliable time source. Second, a machine can itself act as a time source for other computers in the network. The goal is twofold—maintaining the absolute time and synchronizing the system time of all machines within a network.

19 The Domain Name System

DNS (domain name system) is needed to resolve the domain names and host names into IP addresses. In this way, the IP address is assigned to the host name jupiter, for example. Before setting up your own name server, read the general information about DNS in Section 13.3, “Name Resolution”. The following configuration examples refer to BIND, the default DNS server.


The purpose of the Dynamic Host Configuration Protocol (DHCP) is to assign network settings centrally (from a server) rather than configuring them locally on every workstation. A host configured to use DHCP does not have control over its own static address. It is enabled to configure itself completely and automatically according to directions from the server. If you use the NetworkManager on the client side, you do not need to configure the client. This is useful if you have changing environments and only one interface active at a time. Never use NetworkManager on a machine that runs a DHCP server.

21 Samba

Using Samba, a Unix machine can be configured as a file and print server for macOS, Windows, and OS/2 machines. Samba has developed into a fully-fledged and rather complex product. Configure Samba with YaST, or by editing the configuration file manually.

22 Sharing File Systems with NFS

Distributing and sharing file systems over a network is a common task in corporate environments. The well-proven network file system (NFS) works with NIS, the yellow pages protocol. For a more secure protocol that works with LDAP and Kerberos, check NFSv4 (default). Combined with pNFS, you can eliminate performance bottlenecks.

NFS with NIS makes a network transparent to the user. With NFS, it is possible to distribute arbitrary file systems over the network. With an appropriate setup, users always find themselves in the same environment regardless of the terminal they currently use.

23 On-Demand Mounting with Autofs

autofs is a program that automatically mounts specified directories on an on-demand basis. It is based on a kernel module for high efficiency, and can manage both local directories and network shares. These automatic mount points are mounted only when they are accessed, and unmounted after a certain period of inactivity. This on-demand behavior saves bandwidth and results in better performance than static mounts managed by /etc/fstab. While autofs is a control script, automount is the command (daemon) that does the actual auto-mounting.

24 The Apache HTTP Server

According to the survey from, the Apache HTTP Server (Apache) is the world's most widely-used Web server. Developed by the Apache Software Foundation (, it is available for most operating systems. openSUSE® Leap includes Apache version 2.4. In this chapter, learn how to install, configure and set up a Web server; how to use SSL, CGI, and additional modules; and how to troubleshoot Apache.

25 Setting Up an FTP Server with YaST

Using the YaST FTP Server module, you can configure your machine to function as an FTP (File Transfer Protocol) server. Anonymous and/or authenticated users can connect to your machine and download files using the FTP protocol. Depending on the configuration, they can also upload files to the FTP server. YaST uses vsftpd (Very Secure FTP Daemon).

26 The Proxy Server Squid

Squid is a widely-used proxy cache for Linux and Unix platforms. This means that it stores requested Internet objects, such as data on a Web or FTP server, on a machine that is closer to the requesting workstation than the server. It can be set up in multiple hierarchies to assure optimal response times and low bandwidth usage, even in modes that are transparent to end users. Additional software like squidGuard can be used to filter Web content.

17 SLP


Configuring a network client requires detailed knowledge about services provided over the network (such as printing or LDAP, for example). To make it easier to configure such services on a network client, the service location protocol (SLP) was developed. SLP makes the availability and configuration data of selected services known to all clients in the local network. Applications that support SLP can use this information to be configured automatically.

openSUSE® Leap supports installation using installation sources provided with SLP and contains many system services with integrated support for SLP. You can use SLP to provide networked clients with central functions, such as an installation server, file server, or print server on your system. Services that offer SLP support include cupsd, login, ntp, openldap2, postfix, rpasswd, rsyncd, saned, sshd (via fish), vnc, and ypserv.

All packages necessary to use SLP services on a network client are installed by default. However, if you want to provide services via SLP, check that the openslp-server package is installed.

17.1 The SLP Front-End slptool

slptool is a command line tool to query and register SLP services. The query functions are useful for diagnostic purposes. The most important slptool subcommands are listed below. slptool --help lists all available options and functions.


List all service types available on the network.

tux >  slptool findsrvtypes
findsrvs service type

List all servers providing service type

tux >  slptool findsrvs service:ntp
findattrs service type//host

List attributes for service type on host

tux >  slptool findattrs service:ntp://
register service type//host:port "(attribute=value),(attribute=value)"

Registers service type on host with an optional list of attributes

slptool register service:ntp:// \
deregister service type//host

De-registers service type on host

slptool deregister service:ntp://

For more information run slptool --help.

17.2 Providing Services via SLP

To provide SLP services, the SLP daemon (slpd) must be running. Like most system services in openSUSE Leap, slpd is controlled by means of a separate start script. After the installation, the daemon is inactive by default. To activate it for the current session, run sudo systemctl start slpd. If slpd should be activated on system start-up, run sudo systemctl enable slpd.

Many applications in openSUSE Leap have integrated SLP support via the libslp library. If a service has not been compiled with SLP support, use one of the following methods to make it available via SLP:

Static Registration with /etc/slp.reg.d

Create a separate registration file for each new service. The following example registers a scanner service:

## Register a saned service on this system
## en means english language
## 65535 disables the timeout, so the service registration does
## not need refreshes
description=SANE scanner daemon

The most important line in this file is the service URL, which begins with service:. This contains the service type (scanner.sane) and the address under which the service is available on the server. $HOSTNAME is automatically replaced with the full host name. The name of the TCP port on which the relevant service can be found follows, separated by a colon. Then enter the language in which the service should appear and the duration of registration in seconds. These should be separated from the service URL by commas. Set the value for the duration of registration between 0 and 65535. 0 prevents registration. 65535 removes all restrictions.

The registration file also contains the two variables watch-port-tcp and description. watch-port-tcp links the SLP service announcement to whether the relevant service is active by having slpd check the status of the service. The second variable contains a more precise description of the service that is displayed in suitable browsers.

Tip: YaST and SLP

Some services brokered by YaST, such as an installation server or YOU server, perform this registration automatically when you activate SLP in the module dialogs. YaST then creates registration files for these services.

Static Registration with /etc/slp.reg

The only difference between this method and the procedure with /etc/slp.reg.d is that all services are grouped within a central file.

Dynamic Registration with slptool

If a service needs to be registered dynamically without the need of configuration files, use the slptool command line utility. The same utility can also be used to de-register an existing service offering without restarting slpd. See Section 17.1, “The SLP Front-End slptool for details.

17.2.1 Setting up an SLP Installation Server

Announcing the installation data via SLP within your network makes the network installation much easier, since the installation data such as IP address of the server or the path to the installation media are automatically required via SLP query.

17.3 For More Information

RFC 2608, 2609, 2610

RFC 2608 generally deals with the definition of SLP. RFC 2609 deals with the syntax of the service URLs used in greater detail and RFC 2610 deals with DHCP via SLP.

The home page of the OpenSLP project.


This directory contains the documentation for SLP coming with the openslp-server package, including a README.SUSE containing the openSUSE Leap details, the RFCs, and two introductory HTML documents. Programmers who want to use the SLP functions will find more information in the Programmers Guide that is included in the openslp-devel package that is provided with the SUSE Software Development Kit.

18 Time Synchronization with NTP


The NTP (network time protocol) mechanism is a protocol for synchronizing the system time over the network. First, a machine can obtain the time from a server that is a reliable time source. Second, a machine can itself act as a time source for other computers in the network. The goal is twofold—maintaining the absolute time and synchronizing the system time of all machines within a network.

Maintaining an exact system time is important in many situations. The built-in hardware clock does often not meet the requirements of applications such as databases or clusters. Manual correction of the system time would lead to severe problems because, for example, a backward leap can cause malfunction of critical applications. Within a network, it is usually necessary to synchronize the system time of all machines, but manual time adjustment is a bad approach. NTP provides a mechanism to solve these problems. The NTP service continuously adjusts the system time with reliable time servers in the network. It further enables the management of local reference clocks, such as radio-controlled clocks.


To enable time synchronization by means of active directory, follow the instructions found at Book “Security Guide”, Chapter 6 “Active Directory Support”, Section 6.3.3 “ Joining Active Directory Using Windows Domain Membership ”, Joining an Active Directory Domain Using Windows Domain Membership .

18.1 Configuring an NTP Client with YaST

The NTP daemon (ntpd) coming with the ntp package is preset to use the local computer clock as a time reference. Using the hardware clock, however, only serves as a fallback for cases where no time source of better precision is available. YaST simplifies the configuration of an NTP client.

18.1.1 Basic Configuration

The YaST NTP client configuration (Network Services › NTP Configuration) consists of tabs. Set the start mode of ntpd and the server to query on the General Settings tab.

Only Manually

Select Only Manually, if you want to manually start the ntpd daemon.

Synchronize without Daemon

Select Synchronize without Daemon to set the system time periodically without a permanently running ntpd. You can set the Interval of the Synchronization in Minutes.

Now and On Boot

Select Now and On Boot to start ntpd automatically when the system is booted. This setting is recommended.

18.1.2 Changing Basic Configuration

The servers and other time sources for the client to query are listed in the lower part of the General Settings tab. Modify this list as needed with Add, Edit, and Delete. Display Log provides the possibility to view the log files of your client.

Click Add to add a new source of time information. In the following dialog, select the type of source with which the time synchronization should be made. The following options are available:

YaST: NTP Server
Figure 18.1: YaST: NTP Server

In the pull-down Select list (see Figure 18.1, “YaST: NTP Server”), determine whether to set up time synchronization using a time server from your local network (Local NTP Server) or an Internet-based time server that takes care of your time zone (Public NTP Server). For a local time server, click Lookup to start an SLP query for available time servers in your network. Select the most suitable time server from the list of search results and exit the dialog with OK. For a public time server, select your country (time zone) and a suitable server from the list under Public NTP Server then exit the dialog with OK. In the main dialog, test the availability of the selected server with Test. Options allows you to specify additional options for ntpd.

Using Access Control Options, you can restrict the actions that the remote computer can perform with the daemon running on your computer. This field is enabled only after checking Restrict NTP Service to Configured Servers Only on the Security Settings tab (see Figure 18.2, “Advanced NTP Configuration: Security Settings”). The options correspond to the restrict clauses in /etc/ntp.conf. For example, nomodify notrap noquery disallows the server to modify NTP settings of your computer and to use the trap facility (a remote event logging feature) of your NTP daemon. Using these restrictions is recommended for servers out of your control (for example, on the Internet).

Refer to /usr/share/doc/packages/ntp-doc (part of the ntp-doc package) for detailed information.


A peer is a machine to which a symmetric relationship is established: it acts both as a time server and as a client. To use a peer in the same network instead of a server, enter the address of the system. The rest of the dialog is identical to the Server dialog.

Radio Clock

To use a radio clock in your system for the time synchronization, enter the clock type, unit number, device name, and other options in this dialog. Click Driver Calibration to fine-tune the driver. Detailed information about the operation of a local radio clock is available in /usr/share/doc/packages/ntp-doc/refclock.html.

Outgoing Broadcast

Time information and queries can also be transmitted by broadcast in the network. In this dialog, enter the address to which such broadcasts should be sent. Do not activate broadcasting unless you have a reliable time source like a radio controlled clock.

Incoming Broadcast

If you want your client to receive its information via broadcast, enter the address from which the respective packets should be accepted in this fields.

Advanced NTP Configuration: Security Settings
Figure 18.2: Advanced NTP Configuration: Security Settings

In the Security Settings tab (see Figure 18.2, “Advanced NTP Configuration: Security Settings”), determine whether ntpd should be started in a chroot jail. By default, Run NTP Daemon in Chroot Jail is not activated. The chroot jail option increases the security in the event of an attack over ntpd, as it prevents the attacker from compromising the entire system.

Restrict NTP Service to Configured Servers Only increases the security of your system by disallowing remote computers to view and modify NTP settings of your computer and to use the trap facility for remote event logging. After being enabled, these restrictions apply to all remote computers, unless you override the access control options for individual computers in the list of time sources in the General Settings tab. For all other remote computers, only querying for local time is allowed.

Enable Open Port in Firewall if SuSEFirewall2 is active (which it is by default). If you leave the port closed, it is not possible to establish a connection to the time server.

18.2 Manually Configuring NTP in the Network

The easiest way to use a time server in the network is to set server parameters. For example, if a time server called is reachable from the network, add its name to the file /etc/ntp.conf by adding the following line:


To add more time servers, insert additional lines with the keyword server. After initializing ntpd with the command systemctl start ntp, it takes about one hour until the time is stabilized and the drift file for correcting the local computer clock is created. With the drift file, the systematic error of the hardware clock can be computed when the computer is powered on. The correction is used immediately, resulting in a higher stability of the system time.

There are two possible ways to use the NTP mechanism as a client: First, the client can query the time from a known server in regular intervals. With many clients, this approach can cause a high load on the server. Second, the client can wait for NTP broadcasts sent out by broadcast time servers in the network. This approach has the disadvantage that the quality of the server is unknown and a server sending out wrong information can cause severe problems.

If the time is obtained via broadcast, you do not need the server name. In this case, enter the line broadcastclient in the configuration file /etc/ntp.conf. To use one or more known time servers exclusively, enter their names in the line starting with servers.

18.3 Dynamic Time Synchronization at Runtime

If the system boots without network connection, ntpd starts up, but it cannot resolve DNS names of the time servers set in the configuration file. This can happen if you use NetworkManager with an encrypted Wi-Fi.

If you want ntpd to resolve DNS names at runtime, you must set the dynamic option. Then, when the network is establish some time after booting, ntpd looks up the names again and can reach the time servers to get the time.

Manually edit /etc/ntp.conf and add dynamic to one or more server entries:

server dynamic

Or use YaST and proceed as follows:

  1. In YaST click Network Services › NTP Configuration.

  2. Select the server you want to configure. Then click Edit.

  3. Activate the Options field and add dynamic. Separate it with a space, if there are already other options entered.

  4. Click Ok to close the edit dialog. Repeat the previous step to change all servers as wanted.

  5. Finally click Ok to save the settings.

18.4 Setting Up a Local Reference Clock

The software package ntpd contains drivers for connecting local reference clocks. A list of supported clocks is available in the ntp-doc package in the file /usr/share/doc/packages/ntp-doc/refclock.html. Every driver is associated with a number. In NTP, the actual configuration takes place by means of pseudo IP addresses. The clocks are entered in the file /etc/ntp.conf as though they existed in the network. For this purpose, they are assigned special IP addresses in the form 127.127.t.u. Here, t stands for the type of the clock and determines which driver is used and u for the unit, which determines the interface used.

Normally, the individual drivers have special parameters that describe configuration details. The file /usr/share/doc/packages/ntp-doc/drivers/driverNN.html (where NN is the number of the driver) provides information about the particular type of clock. For example, the type 8 clock (radio clock over serial interface) requires an additional mode that specifies the clock more precisely. The Conrad DCF77 receiver module, for example, has mode 5. To use this clock as a preferred reference, specify the keyword prefer. The complete server line for a Conrad DCF77 receiver module would be:

server mode 5 prefer

Other clocks follow the same pattern. Following the installation of the ntp-doc package, the documentation for NTP is available in the directory /usr/share/doc/packages/ntp-doc. The file /usr/share/doc/packages/ntp-doc/refclock.html provides links to the driver pages describing the driver parameters.

19 The Domain Name System


DNS (domain name system) is needed to resolve the domain names and host names into IP addresses. In this way, the IP address is assigned to the host name jupiter, for example. Before setting up your own name server, read the general information about DNS in Section 13.3, “Name Resolution”. The following configuration examples refer to BIND, the default DNS server.

19.1 DNS Terminology


The domain name space is divided into regions called zones. For instance, if you have, you have the example section (or zone) of the com domain.

DNS server

The DNS server is a server that maintains the name and IP information for a domain. You can have a primary DNS server for master zone, a secondary server for slave zone, or a slave server without any zones for caching.

Master zone DNS server

The master zone includes all hosts from your network and a DNS server master zone stores up-to-date records for all the hosts in your domain.

Slave zone DNS server

A slave zone is a copy of the master zone. The slave zone DNS server obtains its zone data with zone transfer operations from its master server. The slave zone DNS server responds authoritatively for the zone as long as it has valid (not expired) zone data. If the slave cannot obtain a new copy of the zone data, it stops responding for the zone.


Forwarders are DNS servers to which your DNS server should send queries it cannot answer. To enable different configuration sources in one configuration, netconfig is used (see also man 8 netconfig).


The record is information about name and IP address. Supported records and their syntax are described in BIND documentation. Some special records are:

NS record

An NS record tells name servers which machines are in charge of a given domain zone.

MX record

The MX (mail exchange) records describe the machines to contact for directing mail across the Internet.

SOA record

SOA (Start of Authority) record is the first record in a zone file. The SOA record is used when using DNS to synchronize data between multiple computers.

19.2 Installation

To install a DNS server, start YaST and select Software › Software Management. Choose View › Patterns and select DHCP and DNS Server. Confirm the installation of the dependent packages to finish the installation process.

19.3 Configuration with YaST

Use the YaST DNS module to configure a DNS server for the local network. When starting the module for the first time, a wizard starts, prompting you to make a few decisions concerning administration of the server. Completing this initial setup produces a basic server configuration. Use the expert mode to deal with more advanced configuration tasks, such as setting up ACLs, logging, TSIG keys, and other options.

19.3.1 Wizard Configuration

The wizard consists of three steps or dialogs. At the appropriate places in the dialogs, you can enter the expert configuration mode.

  1. When starting the module for the first time, the Forwarder Settings dialog, shown in Figure 19.1, “DNS Server Installation: Forwarder Settings”, opens. The Local DNS Resolution Policy allows to set the following options:

    • Merging forwarders is disabled

    • Automatic merging

    • Merging forwarders is enabled

    • Custom configuration—If Custom configuration is selected, Custom policy can be specified; by default (with Automatic merging selected), Custom policy is set to auto, but here you can either set interface names or select from the two special policy names STATIC and STATIC_FALLBACK.

    In Local DNS Resolution Forwarder, specify which service to use: Using system name servers, This name server (bind), or Local dnsmasq server.

    For more information about all these settings, see man 8 netconfig.

    DNS Server Installation: Forwarder Settings
    Figure 19.1: DNS Server Installation: Forwarder Settings

    Forwarders are DNS servers to which your DNS server sends queries it cannot answer itself. Enter their IP address and click Add.

  2. The DNS Zones dialog consists of several parts and is responsible for the management of zone files, described in Section 19.6, “Zone Files”. For a new zone, provide a name for it in Name. To add a reverse zone, the name must end in Finally, select the Type (master, slave, or forward). See Figure 19.2, “DNS Server Installation: DNS Zones”. Click Edit to configure other settings of an existing zone. To remove a zone, click Delete.

    DNS Server Installation: DNS Zones
    Figure 19.2: DNS Server Installation: DNS Zones
  3. In the final dialog, you can open the DNS port in the firewall by clicking Open Port in Firewall. Then decide whether to start the DNS server when booting (On or Off). You can also activate LDAP support. See Figure 19.3, “DNS Server Installation: Finish Wizard”.

    DNS Server Installation: Finish Wizard
    Figure 19.3: DNS Server Installation: Finish Wizard

19.3.2 Expert Configuration

After starting the module, YaST opens a window displaying several configuration options. Completing it results in a DNS server configuration with the basic functions in place: Start-Up

Under Start-Up, define whether the DNS server should be started when the booting the system or manually. To start the DNS server immediately, click Start DNS Server Now. To stop the DNS server, click Stop DNS Server Now. To save the current settings, select Save Settings and Reload DNS Server Now. You can open the DNS port in the firewall with Open Port in Firewall and modify the firewall settings with Firewall Details.

By selecting LDAP Support Active, the zone files are managed by an LDAP database. Any changes to zone data written to the LDAP database are picked up by the DNS server when it is restarted or prompted to reload its configuration. Forwarders

If your local DNS server cannot answer a request, it tries to forward the request to a Forwarder, if configured so. This forwarder may be added manually to the Forwarder List. If the forwarder is not static like in dial-up connections, netconfig handles the configuration. For more information about netconfig, see man 8 netconfig. Basic Options

In this section, set basic server options. From the Option menu, select the desired item then specify the value in the corresponding text box. Include the new entry by selecting Add. Logging

To set what the DNS server should log and how, select Logging. Under Log Type, specify where the DNS server should write the log data. Use the system-wide log by selecting System Log or specify a different file by selecting File. In the latter case, additionally specify a name, the maximum file size in megabytes and the number of log file versions to store.

Further options are available under Additional Logging. Enabling Log All DNS Queries causes every query to be logged, in which case the log file could grow extremely large. For this reason, it is not a good idea to enable this option for other than debugging purposes. To log the data traffic during zone updates between DHCP and DNS server, enable Log Zone Updates. To log the data traffic during a zone transfer from master to slave, enable Log Zone Transfer. See Figure 19.4, “DNS Server: Logging”.

DNS Server: Logging
Figure 19.4: DNS Server: Logging ACLs

Use this dialog to define ACLs (access control lists) to enforce access restrictions. After providing a distinct name under Name, specify an IP address (with or without netmask) under Value in the following fashion:

{ 192.168.1/24; }

The syntax of the configuration file requires that the address ends with a semicolon and is put into curly braces. TSIG Keys

The main purpose of TSIGs (transaction signatures) is to secure communications between DHCP and DNS servers. They are described in Section 19.8, “Secure Transactions”.

To generate a TSIG key, enter a distinctive name in the field labeled Key ID and specify the file where the key should be stored (Filename). Confirm your choices with Generate.

To use a previously created key, leave the Key ID field blank and select the file where it is stored under Filename. After that, confirm with Add. DNS Zones (Adding a Slave Zone)

To add a slave zone, select DNS Zones, choose the zone type Slave, write the name of the new zone, and click Add.

In the Zone Editor sub-dialog under Master DNS Server IP, specify the master from which the slave should pull its data. To limit access to the server, select one of the ACLs from the list. DNS Zones (Adding a Master Zone)

To add a master zone, select DNS Zones, choose the zone type Master, write the name of the new zone, and click Add. When adding a master zone, a reverse zone is also needed. For example, when adding the zone that points to hosts in a subnet, you should also add a reverse zone for the IP-address range covered. By definition, this should be named DNS Zones (Editing a Master Zone)

To edit a master zone, select DNS Zones, select the master zone from the table, and click Edit. The dialog consists of several pages: Basics (the one opened first), NS Records, MX Records, SOA, and Records.

The basic dialog, shown in Figure 19.5, “DNS Server: Zone Editor (Basics)”, lets you define settings for dynamic DNS and access options for zone transfers to clients and slave name servers. To permit the dynamic updating of zones, select Allow Dynamic Updates as well as the corresponding TSIG key. The key must have been defined before the update action starts. To enable zone transfers, select the corresponding ACLs. ACLs must have been defined already.

In the Basics dialog, select whether to enable zone transfers. Use the listed ACLs to define who can download zones.

DNS Server: Zone Editor (Basics)
Figure 19.5: DNS Server: Zone Editor (Basics)
Zone Editor (NS Records)

The NS Records dialog allows you to define alternative name servers for the zones specified. Make sure that your own name server is included in the list. To add a record, enter its name under Name Server to Add then confirm with Add. See Figure 19.6, “DNS Server: Zone Editor (NS Records)”.

DNS Server: Zone Editor (NS Records)
Figure 19.6: DNS Server: Zone Editor (NS Records)
Zone Editor (MX Records)

To add a mail server for the current zone to the existing list, enter the corresponding address and priority value. After doing so, confirm by selecting Add. See Figure 19.7, “DNS Server: Zone Editor (MX Records)”.

DNS Server: Zone Editor (MX Records)
Figure 19.7: DNS Server: Zone Editor (MX Records)
Zone Editor (SOA)

This page allows you to create SOA (start of authority) records. For an explanation of the individual options, refer to Example 19.6, “The /var/lib/named/ File”. Changing SOA records is not supported for dynamic zones managed via LDAP.

DNS Server: Zone Editor (SOA)
Figure 19.8: DNS Server: Zone Editor (SOA)
Zone Editor (Records)

This dialog manages name resolution. In Record Key, enter the host name then select its type. The A type represents the main entry. The value for this should be an IP address (IPv4). Use AAAA for IPv6 addresses. CNAME is an alias. Use the types NS and MX for detailed or partial records that expand on the information provided in the NS Records and MX Records tabs. These three types resolve to an existing A record. PTR is for reverse zones. It is the opposite of an A record, for example: IN A IN PTR Adding Reverse Zones

To add a reverse zone, follow this procedure:

  1. Start YaST › DNS Server › DNS Zones.

  2. If you have not added a master forward zone, add it and Edit it.

  3. In the Records tab, fill the corresponding Record Key and Value, then add the record with Add and confirm with OK. If YaST complains about a non-existing record for a name server, add it in the NS Records tab.

    Adding a Record for a Master Zone
    Figure 19.9: Adding a Record for a Master Zone
  4. Back in the DNS Zones window, add a reverse master zone.

    Adding a Reverse Zone
    Figure 19.10: Adding a Reverse Zone
  5. Edit the reverse zone, and in the Records tab, you can see the PTR: Reverse translation record type. Add the corresponding Record Key and Value, then click Add and confirm with OK.

    Adding a Reverse Record
    Figure 19.11: Adding a Reverse Record

    Add a name server record if needed.

Tip: Editing the Reverse Zone

After adding a forward zone, go back to the main menu and select the reverse zone for editing. There in the tab Basics activate the check box Automatically Generate Records From and select your forward zone. That way, all changes to the forward zone are automatically updated in the reverse zone.

19.4 Starting the BIND Name Server

On a openSUSE® Leap system, the name server BIND (Berkeley Internet Name Domain) comes preconfigured so it can be started right after installation without any problems. If you already have a functioning Internet connection and have entered as the name server address for localhost in /etc/resolv.conf, you normally already have a working name resolution without needing to know the DNS of the provider. BIND carries out name resolution via the root name server, a notably slower process. Normally, the DNS of the provider should be entered with its IP address in the configuration file /etc/named.conf under forwarders to ensure effective and secure name resolution. If this works so far, the name server runs as a pure caching-only name server. Only when you configure its own zones it becomes a proper DNS. Find a simple example documented in /usr/share/doc/packages/bind/config.

Tip: Automatic Adaptation of the Name Server Information

Depending on the type of Internet connection or the network connection, the name server information can automatically be adapted to the current conditions. To do this, set the NETCONFIG_DNS_POLICY variable in the /etc/sysconfig/network/config file to auto.

However, do not set up an official domain until one is assigned to you by the responsible institution. Even if you have your own domain and it is managed by the provider, you are better off not using it, because BIND would otherwise not forward requests for this domain. The Web server at the provider, for example, would not be accessible for this domain.

To start the name server, enter the command systemctl start named as root. Check with systemctl status named whether named (as the name server process is called) has been started successfully. Test the name server immediately on the local system with the host or dig programs, which should return localhost as the default server with the address If this is not the case, /etc/resolv.conf probably contains an incorrect name server entry or the file does not exist. For the first test, enter host, which should always work. If you get an error message, use systemctl status named to see whether the server is actually running. If the name server does not start or behaves unexpectedly, check the output of journalctl -e.

To use the name server of the provider (or one already running on your network) as the forwarder, enter the corresponding IP address or addresses in the options section under forwarders. The addresses included in Example 19.1, “Forwarding Options in named.conf” are examples only. Adjust these entries to your own setup.

Example 19.1: Forwarding Options in named.conf
options {
        directory "/var/lib/named";
        forwarders {;; };
        listen-on {;; };
        allow-query { 127/8; 192.168/16 };
        notify no;

The options entry is followed by entries for the zone, localhost, and The type hint entry under . should always be present. The corresponding files do not need to be modified and should work as they are. Also make sure that each entry is closed with a ; and that the curly braces are in the correct places. After changing the configuration file /etc/named.conf or the zone files, tell BIND to reread them with systemctl reload named. Achieve the same by stopping and restarting the name server with systemctl restart named. Stop the server at any time by entering systemctl stop named.

19.5 The /etc/named.conf Configuration File

All the settings for the BIND name server itself are stored in the /etc/named.conf file. However, the zone data for the domains to handle (consisting of the host names, IP addresses, and so on) are stored in separate files in the /var/lib/named directory. The details of this are described later.

/etc/named.conf is roughly divided into two areas. One is the options section for general settings and the other consists of zone entries for the individual domains. A logging section and acl (access control list) entries are optional. Comment lines begin with a # sign or //. A minimal /etc/named.conf is shown in Example 19.2, “A Basic /etc/named.conf”.

Example 19.2: A Basic /etc/named.conf
options {
        directory "/var/lib/named";
        forwarders {; };
        notify no;

zone "localhost" in {
       type master;
       file "";

zone "" in {
        type master;
        file "";

zone "." in {
        type hint;
        file "root.hint";

19.5.1 Important Configuration Options

directory "filename";

Specifies the directory in which BIND can find the files containing the zone data. Usually, this is /var/lib/named.

forwarders { ip-address; };

Specifies the name servers (mostly of the provider) to which DNS requests should be forwarded if they cannot be resolved directly. Replace ip-address with an IP address like

forward first;

Causes DNS requests to be forwarded before an attempt is made to resolve them via the root name servers. Instead of forward first, forward only can be written to have all requests forwarded and none sent to the root name servers. This makes sense for firewall configurations.

listen-on port 53 {; ip-address; };

Tells BIND on which network interfaces and port to accept client queries. port 53 does not need to be specified explicitly, because 53 is the default port. Enter to permit requests from the local host. If you omit this entry entirely, all interfaces are used by default.

listen-on-v6 port 53 {any; };

Tells BIND on which port it should listen for IPv6 client requests. The only alternative to any is none. As far as IPv6 is concerned, the server only accepts wild card addresses.

query-source address * port 53;

This entry is necessary if a firewall is blocking outgoing DNS requests. This tells BIND to post requests externally from port 53 and not from any of the high ports above 1024.

query-source-v6 address * port 53;

Tells BIND which port to use for IPv6 queries.

allow-query {; net; };

Defines the networks from which clients can post DNS requests. Replace net with address information like The /24 at the end is an abbreviated expression for the netmask (in this case

allow-transfer ! *;;

Controls which hosts can request zone transfers. In the example, such requests are completely denied with ! *. Without this entry, zone transfers can be requested from anywhere without restrictions.

statistics-interval 0;

In the absence of this entry, BIND generates several lines of statistical information per hour in the system's journal. Set it to 0 to suppress these statistics completely or set an interval in minutes.

cleaning-interval 720;

This option defines at which time intervals BIND clears its cache. This triggers an entry in the system's journal each time it occurs. The time specification is in minutes. The default is 60 minutes.

interface-interval 0;

BIND regularly searches the network interfaces for new or nonexistent interfaces. If this value is set to 0, this is not done and BIND only listens at the interfaces detected at start-up. Otherwise, the interval can be defined in minutes. The default is sixty minutes.

notify no;

no prevents other name servers from being informed when changes are made to the zone data or when the name server is restarted.

For a list of available options, read the manual page man 5 named.conf.

19.5.2 Logging

What, how, and where logging takes place can be extensively configured in BIND. Normally, the default settings should be sufficient. Example 19.3, “Entry to Disable Logging”, shows the simplest form of such an entry and completely suppresses any logging.

Example 19.3: Entry to Disable Logging
logging {
        category default { null; };

19.5.3 Zone Entries

Example 19.4: Zone Entry for
zone "" in {
      type master;
      file "";
      notify no;

After zone, specify the name of the domain to administer ( followed by in and a block of relevant options enclosed in curly braces, as shown in Example 19.4, “Zone Entry for”. To define a slave zone, switch the type to slave and specify a name server that administers this zone as master (which, in turn, may be a slave of another master), as shown in Example 19.5, “Zone Entry for”.

Example 19.5: Zone Entry for
zone "" in {
      type slave;
      file "slave/";
      masters {; }; 

The zone options:

type master;

By specifying master, tell BIND that the zone is handled by the local name server. This assumes that a zone file has been created in the correct format.

type slave;

This zone is transferred from another name server. It must be used together with masters.

type hint;

The zone . of the hint type is used to set the root name servers. This zone definition can be left as is.

file or file slave/;

This entry specifies the file where zone data for the domain is located. This file is not required for a slave, because this data is pulled from another name server. To differentiate master and slave files, use the directory slave for the slave files.

masters { server-ip-address; };

This entry is only needed for slave zones. It specifies from which name server the zone file should be transferred.

allow-update {! *; };

This option controls external write access, which would allow clients to make a DNS entry—something not normally desirable for security reasons. Without this entry, zone updates are not allowed. The above entry achieves the same because ! * effectively bans any such activity.

19.6 Zone Files

Two types of zone files are needed. One assigns IP addresses to host names and the other does the reverse: it supplies a host name for an IP address.

Tip: Using the Dot (Period, Fullstop) in Zone Files

The "." has an important meaning in the zone files. If host names are given without a final dot (.), the zone is appended. Complete host names specified with a full domain name must end with a dot (.) to avoid having the domain added to it again. A missing or wrongly placed "." is probably the most frequent cause of name server configuration errors.

The first case to consider is the zone file, responsible for the domain, shown in Example 19.6, “The /var/lib/named/ File”.

Example 19.6: The /var/lib/named/ File
1.  $TTL 2D
2. IN SOA      dns ( 
3.               2003072441  ; serial
4.               1D          ; refresh
5.               2H          ; retry
6.               1W          ; expiry
7.               2D )        ; minimum
9.               IN NS       dns 
10.              IN MX       10 mail
12. gate         IN A 
13.              IN A 
14. dns          IN A 
15. mail         IN A 
16. jupiter      IN A
17. venus        IN A
18. saturn       IN A
19. mercury      IN A
20. ntp          IN CNAME    dns 
21. dns6         IN A6  0    2002:c0a8:174::
Line 1:

$TTL defines the default time to live that should apply to all the entries in this file. In this example, entries are valid for a period of two days (2 D).

Line 2:

This is where the SOA (start of authority) control record begins:

  • The name of the domain to administer is in the first position. This ends with ".", because otherwise the zone would be appended a second time. Alternatively, @ can be entered here, in which case the zone would be extracted from the corresponding entry in /etc/named.conf.

  • After IN SOA is the name of the name server in charge as master for this zone. The name is expanded from dns to, because it does not end with a ".".

  • An e-mail address of the person in charge of this name server follows. Because the @ sign already has a special meaning, "." is entered here instead. For the entry must read The "." must be included at the end to prevent the zone from being added.

  • The ( includes all lines up to ) into the SOA record.

Line 3:

The serial number is an arbitrary number that is increased each time this file is changed. It is needed to inform the secondary name servers (slave servers) of changes. For this, a 10 digit number of the date and run number, written as YYYYMMDDNN, has become the customary format.

Line 4:

The refresh rate specifies the time interval at which the secondary name servers verify the zone serial number. In this case, one day.

Line 5:

The retry rate specifies the time interval at which a secondary name server, in case of error, attempts to contact the primary server again. Here, two hours.

Line 6:

The expiration time specifies the time frame after which a secondary name server discards the cached data if it has not regained contact to the primary server. Here, a week.

Line 7:

The last entry in the SOA record specifies the negative caching TTL—the time for which results of unresolved DNS queries from other servers may be cached.

Line 9:

The IN NS specifies the name server responsible for this domain. dns is extended to because it does not end with a ".". There can be several lines like this—one for the primary and one for each secondary name server. If notify is not set to no in /etc/named.conf, all the name servers listed here are informed of the changes made to the zone data.

Line 10:

The MX record specifies the mail server that accepts, processes, and forwards e-mails for the domain In this example, this is the host The number in front of the host name is the preference value. If there are multiple MX entries, the mail server with the smallest value is taken first and, if mail delivery to this server fails, an attempt is made with the next higher value.

Lines 12–19:

These are the actual address records where one or more IP addresses are assigned to host names. The names are listed here without a "." because they do not include their domain, so is added to all of them. Two IP addresses are assigned to the host gate, as it has two network cards. Wherever the host address is a traditional one (IPv4), the record is marked with A. If the address is an IPv6 address, the entry is marked with AAAA.

Note: IPv6 Syntax

The IPv6 record has a slightly different syntax than IPv4. Because of the fragmentation possibility, it is necessary to provide information about missed bits before the address. To fill up the IPv6 address with the needed number of 0, add two colons at the correct place in the address.

pluto     AAAA 2345:00C1:CA11::1234:5678:9ABC:DEF0
pluto     AAAA 2345:00D2:DA11::1234:5678:9ABC:DEF0
Line 20:

The alias ntp can be used to address dns (CNAME means canonical name).

The pseudo domain is used for the reverse lookup of IP addresses into host names. It is appended to the network part of the address in reverse notation. So 192.168 is resolved into See Example 19.7, “Reverse Lookup”.

Example 19.7: Reverse Lookup
1.  $TTL 2D
2.   IN SOA (
3.                          2003072441      ; serial
4.                          1D              ; refresh
5.                          2H              ; retry
6.                          1W              ; expiry
7.                          2D )            ; minimum
9.                          IN NS 
11. 1.5                     IN PTR 
12. 100.3                   IN PTR 
13. 253.2                   IN PTR
Line 1:

$TTL defines the standard TTL that applies to all entries here.

Line 2:

The configuration file should activate reverse lookup for the network 192.168. Given that the zone is called, it should not be added to the host names. Therefore, all host names are entered in their complete form—with their domain and with a "." at the end. The remaining entries correspond to those described for the previous example.

Lines 3–7:

See the previous example for

Line 9:

Again this line specifies the name server responsible for this zone. This time, however, the name is entered in its complete form with the domain and a "." at the end.

Lines 11–13:

These are the pointer records hinting at the IP addresses on the respective hosts. Only the last part of the IP address is entered at the beginning of the line, without the "." at the end. Appending the zone to this (without the results in the complete IP address in reverse order.

Normally, zone transfers between different versions of BIND should be possible without any problems.

19.7 Dynamic Update of Zone Data

The term dynamic update refers to operations by which entries in the zone files of a master server are added, changed, or deleted. This mechanism is described in RFC 2136. Dynamic update is configured individually for each zone entry by adding an optional allow-update or update-policy rule. Zones to update dynamically should not be edited by hand.

Transmit the entries to update to the server with the command nsupdate. For the exact syntax of this command, check the manual page for nsupdate (man 8 nsupdate). For security reasons, any such update should be performed using TSIG keys as described in Section 19.8, “Secure Transactions”.

19.8 Secure Transactions

Secure transactions can be made with transaction signatures (TSIGs) based on shared secret keys (also called TSIG keys). This section describes how to generate and use such keys.

Secure transactions are needed for communication between different servers and for the dynamic update of zone data. Making the access control dependent on keys is much more secure than merely relying on IP addresses.

Generate a TSIG key with the following command (for details, see man dnssec-keygen):

dnssec-keygen -a hmac-md5 -b 128 -n HOST host1-host2

This creates two files with names similar to these:

Khost1-host2.+157+34265.private Khost1-host2.+157+34265.key

The key itself (a string like ejIkuCyyGJwwuN3xAteKgg==) is found in both files. To use it for transactions, the second file (Khost1-host2.+157+34265.key) must be transferred to the remote host, preferably in a secure way (using scp, for example). On the remote server, the