Applies to openSUSE Leap 42.1

22 Sharing File Systems with NFS

Abstract

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. 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.

Important
Important: Need for DNS

In principle, all exports can be made using IP addresses only. To avoid time-outs, you need a working DNS system. DNS is necessary at least for logging purposes, because the mountd daemon does reverse lookups.

22.1 Terminology

The following are terms used in the YaST module.

Exports

A directory exported by an NFS server, which clients can integrate it into their system.

NFS Client

The NFS client is a system that uses NFS services from an NFS server over the Network File System protocol. The TCP/IP protocol is already integrated into the Linux kernel; there is no need to install any additional software.

NFS Server

The NFS server provides NFS services to clients. A running server depends on the following daemons: nfsd (worker), idmapd (user and group name mappings to IDs and vice versa), statd (file locking), and mountd (mount requests).

NFSv3

NFSv3 is the version 3 implementation, the old stateless NFS that supports client authentication.

NFSv4

NFSv4 is the new version 4 implementation that supports secure user authentication via kerberos. NFSv4 requires one single port only and thus is better suited for environments behind a firewall than NFSv3.

The protocol is specified as http://tools.ietf.org/html/rfc3530.

pNFS

Parallel NFS, a protocol extension of NFSv4. Any pNFS clients can directly access the data on an NFS server.

22.2 Installing NFS Server

The NFS server software is not part of the default installation. If you configure an NFS server as described in Section 22.3, “Configuring NFS Server” you will automatically be prompted to install the required packages. Alternatively, install the package nfs-kernel-server with YaST or Zypper.

Like NIS, NFS is a client/server system. However, a machine can be both—it can supply file systems over the network (export) and mount file systems from other hosts (import).

Note
Note: Mounting NFS Volumes Locally on the Exporting Server

Mounting NFS volumes locally on the exporting server is not supported on SUSE Linux Enterprise systems, as is the case on all Enterprise-class Linux systems.

22.3 Configuring NFS Server

Configuring an NFS server can be done either through YaST or manually. For authentication, NFS can also be combined with Kerberos.

22.3.1 Exporting File Systems with YaST

With YaST, turn a host in your network into an NFS server—a server that exports directories and files to all hosts granted access to it or to all members of a group. Thus, the server can also provide applications without installing the applications locally on every host.

To set up such a server, proceed as follows:

Procedure 22.1: Setting Up an NFS Server
  1. Start YaST and select Network Services › NFS Server; see Figure 22.1, “NFS Server Configuration Tool”. You may be prompted to install additional software.

    NFS Server Configuration Tool
    Figure 22.1: NFS Server Configuration Tool
  2. Activate the Start radio button.

  3. If a firewall is active on your system (SuSEFirewall2), check Open Ports in Firewall. YaST adapts its configuration for the NFS server by enabling the nfs service.

  4. Check whether you want to Enable NFSv4. If you deactivate NFSv4, YaST will only support NFSv3 and NFSv2.

    1. If NFSv4 is selected, additionally enter the appropriate NFSv4 domain name.

      Make sure the name is the same as the one in the /etc/idmapd.conf file of any NFSv4 client that accesses this particular server. This parameter is for the idmapd daemon that is required for NFSv4 support (on both server and client). Leave it as localdomain (the default) if you do not have any special requirements.

  5. Click Enable GSS Security if you need secure access to the server. A prerequisite for this is to have Kerberos installed on your domain and to have both the server and the clients kerberized. Click Next to proceed with the next configuration dialog.

  6. Click Add Directory in the upper half of the dialog to export your directory.

  7. If you have not configured the allowed hosts already, another dialog for entering the client information and options pops up automatically. Enter the host wild card (usually you can leave the default settings as they are).

    There are four possible types of host wild cards that can be set for each host: a single host (name or IP address), netgroups, wild cards (such as * indicating all machines can access the server), and IP networks.

    For more information about these options, see the exports man page.

  8. Click Finish to complete the configuration.

22.3.2 Exporting File Systems Manually

The configuration files for the NFS export service are /etc/exports and /etc/sysconfig/nfs. In addition to these files, /etc/idmapd.conf is needed for the NFSv4 server configuration. To start or restart the services, run the command systemctl restart nfsserver. This also starts the rpc.idmapd if NFSv4 is configured in /etc/sysconfig/nfs. The NFS server depends on a running RPC portmapper. Therefore, it also starts or restarts the portmapper service.

Note
Note: NFSv4

NFSv4 is the latest version of NFS protocol available on openSUSE Leap. Configuring directories for export with NFSv4 is now the same as with NFSv3.

On the previous SUSE Linux Enterprise Server 11 version, the bind mount in /etc/exports was mandatory. It is still supported, but now deprecated.

/etc/exports

The /etc/exports file contains a list of entries. Each entry indicates a directory that is shared and how it is shared. A typical entry in /etc/exports consists of:

/shared/directory   host(option_list)

For example:

/export/data   192.168.1.2(rw,sync)

Here the IP address 192.168.1.2 is used to identify the allowed client. You can also use the name of the host, a wild card indicating a set of hosts (*.abc.com, *, etc.), or netgroups (@my-hosts).

For a detailed explanation of all options and their meaning, refer to the man page of exports (man exports).

/etc/sysconfig/nfs

The /etc/sysconfig/nfs file contains a few parameters that determine NFSv4 server daemon behavior. It is important to set the parameter NFS4_SUPPORT to yes (default). NFS4_SUPPORT determines whether the NFS server supports NFSv4 exports and clients.

Tip
Tip: Mount Options

On SUSE Linux Enterprise prior to version 12, the --bind mount in /etc/exports was mandatory. It is still supported, but now deprecated. Configuring directories for export with NFSv4 is now the same as with NFSv3.

/etc/idmapd.conf

Every user on a Linux machine has a name and an ID. idmapd does the name-to-ID mapping for NFSv4 requests to the server and replies to the client. It must be running on both server and client for NFSv4, because NFSv4 uses only names for its communication.

Make sure that there is a uniform way in which user names and IDs (uid) are assigned to users across machines that might probably be sharing file systems using NFS. This can be achieved by using NIS, LDAP, or any uniform domain authentication mechanism in your domain.

The parameter Domain must be set the same for both, client and server in the /etc/idmapd.conf file. If you are not sure, leave the domain as localdomain in the server and client files. A sample configuration file looks like the following:

[General]
Verbosity = 0
Pipefs-Directory = /var/lib/nfs/rpc_pipefs
Domain = localdomain

[Mapping]
Nobody-User = nobody
Nobody-Group = nobody

For more information, see the man pages of idmapd and idmapd.conf (man idmapd and man idmapd.conf).

After changing /etc/exports or /etc/sysconfig/nfs, start or restart the NFS server service:

systemctl restart nfsserver

After changing /etc/idmapd.conf, reload the configuration file:

killall -HUP rpc.idmapd

If the NFS service needs to start at boot time, run:

systemctl enable nfsserver

22.3.3 NFS with Kerberos

To use Kerberos authentication for NFS, GSS security must be enabled. Select Enable GSS Security in the initial YaST NFS Server dialog. You must have a working Kerberos server to use this feature. YaST does not set up the server but only uses the provided functionality. If you want to use Kerberos authentication in addition to the YaST configuration, complete at least the following steps before running the NFS configuration:

  1. Make sure that both the server and the client are in the same Kerberos domain. They must access the same KDC (Key Distribution Center) server and share their krb5.keytab file (the default location on any machine is /etc/krb5.keytab). For more information about Kerberos, see Book “Security Guide”, Chapter 7 “Network Authentication with Kerberos”.

  2. Start the gssd service on the client with systemctl start gssd.

  3. Start the svcgssd service on the server with systemctl start svcgssd.

For more information about configuring kerberized NFS, refer to the links in Section 22.5, “For More Information”.

22.4 Configuring Clients

To configure your host as an NFS client, you do not need to install additional software. All needed packages are installed by default.

22.4.1 Importing File Systems with YaST

Authorized users can mount NFS directories from an NFS server into the local file tree using the YaST NFS client module. Proceed as follows:

Procedure 22.2: Importing NFS Directories
  1. Start the YaST NFS client module.

  2. Click Add in the NFS Shares tab. Enter the host name of the NFS server, the directory to import, and the mount point at which to mount this directory locally.

  3. When using NFSv4, select Enable NFSv4 in the NFS Settings tab. Additionally, the NFSv4 Domain Name must contain the same value as used by the NFSv4 server. The default domain is localdomain.

  4. To use Kerberos authentication for NFS, GSS security must be enabled. Select Enable GSS Security.

  5. Enable Open Port in Firewall in the NFS Settings tab if you use a Firewall and want to allow access to the service from remote computers. The firewall status is displayed next to the check box.

  6. Click OK to save your changes.

The configuration is written to /etc/fstab and the specified file systems are mounted. When you start the YaST configuration client at a later time, it also reads the existing configuration from this file.

Tip
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 13.4.1.2.5, “Activating the Network Device”, and choose On NFSroot in the Device Activation pane.

22.4.2 Importing File Systems Manually

The prerequisite for importing file systems manually from an NFS server is a running RPC port mapper. The nfs service takes care to start it properly; thus, start it by entering systemctl start nfs as root. Then remote file systems can be mounted in the file system like local partitions using mount:

mount host:remote-pathlocal-path

To import user directories from the nfs.example.com machine, for example, use:

mount nfs.example.com:/home /home

22.4.2.1 Using the Automount Service

The autofs daemon can be used to mount remote file systems automatically. Add the following entry to the /etc/auto.master file:

/nfsmounts /etc/auto.nfs

Now the /nfsmounts directory acts as the root for all the NFS mounts on the client if the auto.nfs file is filled appropriately. The name auto.nfs is chosen for the sake of convenience—you can choose any name. In auto.nfs add entries for all the NFS mounts as follows:

localdata -fstype=nfs server1:/data
nfs4mount -fstype=nfs4 server2:/

Activate the settings with systemctl start autofs as root. In this example, /nfsmounts/localdata, the /data directory of server1, is mounted with NFS and /nfsmounts/nfs4mount from server2 is mounted with NFSv4.

If the /etc/auto.master file is edited while the service autofs is running, the automounter must be restarted for the changes to take effect with systemctl restart autofs.

22.4.2.2 Manually Editing /etc/fstab

A typical NFSv3 mount entry in /etc/fstab looks like this:

nfs.example.com:/data /local/path nfs rw,noauto 0 0

For NFSv4 mounts, use nfs4 instead of nfs in the third column:

nfs.example.com:/data /local/pathv4 nfs4 rw,noauto 0 0

The noauto option prevents the file system from being mounted automatically at start-up. If you want to mount the respective file system manually, it is possible to shorten the mount command specifying the mount point only:

mount /local/path
Note
Note: Mounting at Start-Up

If you do not enter the noauto option, the init scripts of the system will handle the mount of those file systems at start-up.

22.4.3 Parallel NFS (pNFS)

NFS is one of the oldest protocols, developed in the '80s. As such, NFS is usually sufficient if you want to share small files. However, when you want to transfer big files or large numbers of clients want to access data, an NFS server becomes a bottleneck and significantly impacts on the system performance. This is because of files quickly getting bigger, whereas the relative speed of your Ethernet has not fully kept up.

When you request a file from a normal NFS server, the server looks up the file metadata, collects all the data and transfers it over the network to your client. However, the performance bottleneck becomes apparent no matter how small or big the files are:

  • With small files most of the time is spent collecting the metadata.

  • With big files most of the time is spent on transferring the data from server to client.

pNFS, or parallel NFS, overcomes this limitation as it separates the file system metadata from the location of the data. As such, pNFS requires two types of servers:

  • A metadata or control server that handles all the non-data traffic

  • One or more storage server(s) that hold(s) the data

The metadata and the storage servers form a single, logical NFS server. When a client wants to read or write, the metadata server tells the NFSv4 client which storage server to use to access the file chunks. The client can access the data directly on the server.

SUSE Linux Enterprise supports pNFS on the client side only.

22.4.3.1 Configuring pNFS Client With YaST

Proceed as described in Procedure 22.2, “Importing NFS Directories”, but click the pNFS (v4.1) check box and optionally NFSv4 share. YaST will do all the necessary steps and will write all the required options in the file /etc/exports.

22.4.3.2 Configuring pNFS Client Manually

Refer to Section 22.4.2, “Importing File Systems Manually” to start. Most of the configuration is done by the NFSv4 server. For pNFS, the only difference is to add the minorversion option and the metadata server MDS_SERVER to your mount command:

mount -t nfs4 -o minorversion=1 MDS_SERVER MOUNTPOINT

To help with debugging, change the value in the /proc file system:

echo 32767 > /proc/sys/sunrpc/nfsd_debug
echo 32767 > /proc/sys/sunrpc/nfs_debug

22.5 For More Information

In addition to the man pages of exports, nfs, and mount, information about configuring an NFS server and client is available in /usr/share/doc/packages/nfsidmap/README. For further documentation online refer to the following Web sites:

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