10 Basic VM Guest management #

The main window of the Virtual Machine Manager lists all VM Guests for each VM Host Server it is connected to. Each VM Guest entry contains the machine's name, its status (Running, Paused, or Shutoff) displayed as an icon and literally, and a CPU usage bar.

Use the command virsh list to get a list of VM Guests:

For more information and further options, see virsh help list or man 1 virsh.

Opening a graphical console to a VM Guest lets you interact with the machine like a physical host via a VNC connection. If accessing the VNC server requires authentication, you are prompted to enter a user name (if applicable) and a password.

When you click into the VNC console, the cursor is “grabbed” and cannot be used outside the console anymore. To release it, press Alt–Ctrl.

Tip: Seamless (absolute) cursor movement

To prevent the console from grabbing the cursor and to enable seamless cursor movement, add a tablet input device to the VM Guest. See Section 13.5, “Input devices” for more information.

Certain key combinations such as Ctrl–Alt–Del are interpreted by the host system and are not passed to the VM Guest. To pass such key combinations to a VM Guest, open the Send Key menu from the VNC window and choose the desired key combination entry. The Send Key menu is only available when using Virtual Machine Manager and virt-viewer. With Virtual Machine Manager, you can alternatively use the “sticky key” feature as explained in Tip: Passing key combinations to virtual machines.

Note: Supported VNC viewers

Principally all VNC viewers can connect to the console of a VM Guest. However, if you are using SASL authentication and/or TLS/SSL connection to access the guest, the options are limited. Common VNC viewers such as tightvnc or tigervnc support neither SASL authentication nor TLS/SSL. The only supported alternative to Virtual Machine Manager and virt-viewer is Remmina (refer to Book “Reference”, Chapter 4 “Remote graphical sessions with VNC”, Section 4.2 “Remmina: the remote desktop client”).

10.2.1.2 Opening a graphical console with virt-viewer #

  

virt-viewer is a simple VNC viewer with added functionality for displaying VM Guest consoles. For example, it can be started in “wait” mode, where it waits for a VM Guest to start before it connects. It also supports automatically reconnecting to a VM Guest that is rebooted.

virt-viewer addresses VM Guests by name, by ID or by UUID. Use virsh list --all to get this data.

To connect to a guest that is running or paused, use either the ID, UUID, or name. VM Guests that are shut off do not have an ID—you can only connect to them by UUID or name.

Connect to guest with the ID 8

> virt-viewer 8

Connect to the inactive guest named sles12; the connection window will open once the guest starts

> virt-viewer --wait sles12

With the --wait option, the connection will be upheld even if the VM Guest is not running at the moment. When the guest starts, the viewer will be launched.

For more information, see virt-viewer --help or man 1 virt-viewer.

Note: Password input on remote connections with SSH

When using virt-viewer to open a connection to a remote host via SSH, the SSH password needs to be entered twice. The first time for authenticating with libvirt, the second time for authenticating with the VNC server. The second password needs to be provided on the command line where virt-viewer was started.

Accessing the graphical console of a virtual machine requires a graphical environment on the client accessing the VM Guest. As an alternative, virtual machines managed with libvirt can also be accessed from the shell via the serial console and virsh. To open a serial console to a VM Guest named “sles12”, run the following command:

> virsh console sles12

virsh console takes two optional flags: --safe ensures exclusive access to the console, --force disconnects any existing sessions before connecting. Both features need to be supported by the guest operating system.

Being able to connect to a VM Guest via serial console requires that the guest operating system supports serial console access and is properly supported. Refer to the guest operating system manual for more information.

Tip: Enabling serial console access for SUSE Linux Enterprise and openSUSE guests

Serial console access in SUSE Linux Enterprise and openSUSE is disabled by default. To enable it, proceed as follows:

SLES 12 and up/openSUSE

Launch the YaST Boot Loader module and switch to the Kernel Parameters tab. Add console=ttyS0 to the field Optional Kernel Command Line Parameter.

SLES 11

Launch the YaST Boot Loader module and select the boot entry for which to activate serial console access. Choose Edit and add console=ttyS0 to the field Optional Kernel Command Line Parameter. Additionally, edit /etc/inittab and uncomment the line with the following content:

#S0:12345:respawn:/sbin/agetty -L 9600 ttyS0 vt102

Changing a VM Guest's state can be done either from Virtual Machine Manager's main window, or from a VNC window.

In the following examples, the state of a VM Guest named “sles12” is changed.

Save a running VM Guest with the command virsh save and specify the file which it is saved to.

To restore a VM Guest, use virsh restore:

> virsh restore /virtual/saves/opensuse13.vmsave

There are several specific terms used to describe the types of snapshots:

Important: Internal snapshots only

Virtual Machine Manager supports only internal snapshots, either live or offline.

To open the snapshot management view in Virtual Machine Manager, open the VNC window as described in Section 10.2.1.1, “Opening a graphical console with Virtual Machine Manager”. Now either choose View › Snapshots or click Manage VM Snapshots in the toolbar.

The list of existing snapshots for the chosen VM Guest is displayed in the left-hand part of the window. The snapshot that was last started is marked with a green tick. The right-hand part of the window shows details of the snapshot currently marked in the list. These details include the snapshot's title and time stamp, the state of the VM Guest at the time the snapshot was taken and a description. Snapshots of running guests also include a screenshot. The Description can be changed directly from this view. Other snapshot data cannot be changed.

To list all existing snapshots for a domain (admin_server in the following), run the snapshot-list command:

> virsh snapshot-list --domain sle-ha-node1
 Name                 Creation Time             State
------------------------------------------------------------
 sleha_12_sp2_b2_two_node_cluster 2016-06-06 15:04:31 +0200 shutoff
 sleha_12_sp2_b3_two_node_cluster 2016-07-04 14:01:41 +0200 shutoff
 sleha_12_sp2_b4_two_node_cluster 2016-07-14 10:44:51 +0200 shutoff
 sleha_12_sp2_rc3_two_node_cluster 2016-10-10 09:40:12 +0200 shutoff
 sleha_12_sp2_gmc_two_node_cluster 2016-10-24 17:00:14 +0200 shutoff
 sleha_12_sp3_gm_two_node_cluster 2017-08-02 12:19:37 +0200 shutoff
 sleha_12_sp3_rc1_two_node_cluster 2017-06-13 13:34:19 +0200 shutoff
 sleha_12_sp3_rc2_two_node_cluster 2017-06-30 11:51:24 +0200 shutoff
 sleha_15_b6_two_node_cluster 2018-02-07 15:08:09 +0100 shutoff
 sleha_15_rc1_one-node 2018-03-09 16:32:38 +0100 shutoff

The snapshot that was last started is shown with the snapshot-current command:

> virsh snapshot-current --domain admin_server
Basic installation incl. SMT for CLOUD4

Details about a particular snapshot can be obtained by running the snapshot-info command:

> virsh snapshot-info --domain admin_server \
   -name  "Basic installation incl. SMT for CLOUD4"
Name:           Basic installation incl. SMT for CLOUD4
Domain:         admin_server
Current:        yes
State:          shutoff
Location:       internal
Parent:         Basic installation incl. SMT for CLOUD3-HA
Children:       0
Descendants:    0
Metadata:       yes

> virsh snapshot-create-as --domain admin_server1 --name "Snapshot 1"2 \
--description "First snapshot"3

> virsh snapshot-create-as --domain admin_server --name \
 "Offline external snapshot" --disk-only

> virsh snapshot-create-as --domain admin_server --name \
 "Offline external snapshot" \
 --disk-only --diskspec vda,snapshot=external,file=/path/to/snapshot_file

> virsh snapshot-create-as --domain admin_server --name \
 "Offline external snapshot" --live \
 --memspec snapshot=external,file=/path/to/snapshot_file

> virsh snapshot-create-as --domain admin_server --name \
 "Offline external snapshot" --live \
 --memspec snapshot=external,file=/path/to/snapshot_file
 --diskspec vda,snapshot=external,file=/path/to/snapshot_file

> virsh snapshot-delete --domain admin_server --snapshotname "Snapshot 2"

> virsh snapshot-revert --domain admin_server --snapshotname "Snapshot 1"

> virsh snapshot-revert --domain admin_server --current

To delete a VM Guest, it needs to be shut down first. It is not possible to delete a running guest. For information on shutting down, see Section 10.3, “Changing a VM Guest's state: start, stop, pause”.

To delete a VM Guest with virsh, run virsh undefine VM_NAME.

> virsh undefine sles12

There is no option to automatically delete the attached storage files. If they are managed by libvirt, delete them as described in Section 8.2.1.4, “Deleting volumes from a storage pool”.

To successfully migrate a VM Guest to another VM Host Server, the following requirements need to be met:

Important

In order to use the post-copy live migration option, KVM hosts with kernel version 5.11 or newer require setting the unprivileged_userfaultfd system value to 1:

> sudo sysctl -w vm.unprivileged_userfaultfd=1

Since kernel versions prior to 5.11 did not require setting unprivileged_userfaultfd to use the post-copy option, libvirt provides the setting in /usr/lib/sysctl.d/60-qemu-postcopy-migration.conf file to preserve the old behavior.

When using the Virtual Machine Manager to migrate VM Guests, it does not matter on which machine it is started. You can start Virtual Machine Manager on the source or the target host or even on a third host. In the latter case you need to be able to open remote connections to both the target and the source host.

To migrate a VM Guest with virsh migrate, you need to have direct or remote shell access to the VM Host Server, because the command needs to be run on the host. The migration command looks like this:

> virsh migrate [OPTIONS] VM_ID_or_NAME CONNECTION_URI [--migrateuri tcp://REMOTE_HOST:PORT]

The most important options are listed below. See virsh help migrate for a full list.

The following examples use mercury.example.com as the source system and jupiter.example.com as the target system; the VM Guest's name is opensuse131 with Id 37.

Note: Transient compared to persistent migrations

By default virsh migrate creates a temporary (transient) copy of the VM Guest on the target host. A shut down version of the original guest description remains on the source host. A transient copy will be deleted from the server after it is shut down.

To create a permanent copy of a guest on the target host, use the switch --persistent. A shut down version of the original guest description remains on the source host, too. Use the option --undefinesource together with --persistent for a “real” move where a permanent copy is created on the target host and the version on the source host is deleted.

It is not recommended to use --undefinesource without the --persistent option, since this will result in the loss of both VM Guest definitions when the guest is shut down on the target host.

After starting Virtual Machine Manager and connecting to the VM Host Server, a CPU usage graph of all the running guests is displayed.

It is also possible to get information about disk and network usage with this tool, however, you must first activate this in Preferences:

Afterward, the disk and network statistics are also displayed in the main window of the Virtual Machine Manager.

More precise data is available from the VNC window. Open a VNC window as described in Section 10.2.1, “Opening a graphical console”. Choose Details from the toolbar or the View menu. The statistics are displayed from the Performance entry of the left-hand tree menu.

virt-top is a command line tool similar to the well-known process monitoring tool top. virt-top uses libvirt and therefore is capable of showing statistics for VM Guests running on different hypervisors. It is recommended to use virt-top instead of hypervisor-specific tools like xentop.

By default virt-top shows statistics for all running VM Guests. Among the data that is displayed is the percentage of memory used (%MEM) and CPU (%CPU) and the uptime of the guest (TIME). The data is updated regularly (every three seconds by default). The following shows the output on a VM Host Server with seven VM Guests, four of them inactive:

virt-top 13:40:19 - x86_64 8/8CPU 1283MHz 16067MB 7.6% 0.5%
7 domains, 3 active, 3 running, 0 sleeping, 0 paused, 4 inactive D:0 O:0 X:0
CPU: 6.1%  Mem: 3072 MB (3072 MB by guests)

   ID S RDRQ WRRQ RXBY TXBY %CPU %MEM    TIME   NAME
    7 R  123    1  18K  196  5.8  6.0   0:24.35 sled12_sp1
    6 R    1    0  18K    0  0.2  6.0   0:42.51 sles12_sp1
    5 R    0    0  18K    0  0.1  6.0  85:45.67 opensuse_leap
    -                                           (Ubuntu_1410)
    -                                           (debian_780)
    -                                           (fedora_21)
    -                                           (sles11sp3)

By default the output is sorted by ID. Use the following key combinations to change the sort field:

To use any other field for sorting, press Shift–F and select a field from the list. To toggle the sort order, use Shift–R.

virt-top also supports different views on the VM Guests data, which can be changed on-the-fly by pressing the following keys:

virt-top supports more hot keys to change the view of the data and many command line switches that affect the behavior of the program. For more information, see man 1 virt-top.

kvm_stat can be used to trace KVM performance events. It monitors /sys/kernel/debug/kvm, so it needs the debugfs to be mounted. On openSUSE Leap it should be mounted by default. In case it is not mounted, use the following command:

> sudo mount -t debugfs none /sys/kernel/debug

kvm_stat can be used in three different modes:

kvm_stat                    # update in 1 second intervals
kvm_stat -1                 # 1 second snapshot
kvm_stat -l > kvmstats.log  # update in 1 second intervals in log format
                            # can be imported to a spreadsheet

kvm statistics

 efer_reload                  0       0
 exits                 11378946  218130
 fpu_reload               62144     152
 halt_exits              414866     100
 halt_wakeup             260358      50
 host_state_reload       539650     249
 hypercalls                   0       0
 insn_emulation         6227331  173067
 insn_emulation_fail          0       0
 invlpg                  227281      47
 io_exits                113148      18
 irq_exits               168474     127
 irq_injections          482804     123
 irq_window               51270      18
 largepages                   0       0
 mmio_exits                6925       0
 mmu_cache_miss           71820      19
 mmu_flooded              35420       9
 mmu_pde_zapped           64763      20
 mmu_pte_updated              0       0
 mmu_pte_write           213782      29
 mmu_recycled                 0       0
 mmu_shadow_zapped       128690      17
 mmu_unsync                  46      -1
 nmi_injections               0       0
 nmi_window                   0       0
 pf_fixed               1553821     857
 pf_guest               1018832     562
 remote_tlb_flush        174007      37
 request_irq                  0       0
 signal_exits                 0       0
 tlb_flush               394182     148

See http://clalance.blogspot.com/2009/01/kvm-performance-tools.html for further information on how to interpret these values.