Managing guests with virsh
virsh is a command line interface tool for managing guests and the hypervisor.
The virsh tool is built on the libvirt management API and operates as an alternative to the xm command and the graphical guest Manager (virt-manager). virsh can be used in read-only mode by unprivileged users. You can use virsh to execute scripts for the guest machines.
The following tables provide a quick reference for all virsh command line options.
| Command |
Description |
help |
Prints basic help information. |
list |
Lists all guests. |
dumpxml |
Outputs the XML configuration file for the guest. |
create |
Creates a guest from an XML configuration file and starts the new guest. |
start |
Starts an inactive guest. |
destroy |
Forces a guest to stop. |
define |
Outputs an XML configuration file for a guest. |
domid |
Displays the guest's ID. |
domuuid |
Displays the guest's UUID. |
dominfo |
Displays guest information. |
domname |
Displays the guest's name. |
domstate |
Displays the state of a guest. |
quit |
Quits the interactive terminal. |
reboot |
Reboots a guest. |
restore |
Restores a previously saved guest stored in a file. |
resume |
Resumes a paused guest. |
save |
Save the present state of a guest to a file. |
shutdown |
Gracefully shuts down a guest. |
suspend |
Pauses a guest. |
undefine |
Deletes all files associated with a guest. |
migrate |
Migrates a guest to another host. |
Table 28.1. Guest management commands
The following virsh command options manage guest and hypervisor resources:
| Command |
Description |
setmem |
Sets the allocated memory for a guest. |
setmaxmem |
Sets maximum memory limit for the hypervisor. |
setvcpus |
Changes number of virtual CPUs assigned to a guest. |
vcpuinfo |
Displays virtual CPU information about a guest. |
vcpupin |
Controls the virtual CPU affinity of a guest. |
domblkstat |
Displays block device statistics for a running guest. |
domifstat |
Displays network interface statistics for a running guest. |
attach-device |
Attach a device to a guest, using a device definition in an XML file. |
attach-disk |
Attaches a new disk device to a guest. |
attach-interface |
Attaches a new network interface to a guest. |
detach-device |
Detach a device from a guest, takes the same kind of XML descriptions as command attach-device. |
detach-disk |
Detach a disk device from a guest. |
detach-interface |
Detach a network interface from a guest. |
Table 28.2. Resource management options
These are miscellaneous virsh options:
| Command |
Description |
version |
Displays the version of virsh |
nodeinfo |
Outputs information about the hypervisor |
Table 28.3. Miscellaneous options
Connect to a hypervisor session with virsh:
# virsh connect {hostname OR URL}
Where <name> is the machine name of the hypervisor. To initiate a read-only connection, append the above command with -readonly.
Output a guest's XML configuration file with virsh:
# virsh dumpxml {guest-id, guestname or uuid}
This command outputs the guest's XML configuration file to standard out (stdout). You can save the data by piping the output to a file. An example of piping the output to a file called guest.xml:
# virsh dumpxml GuestID > guest.xml
An example of virsh dumpxml output:
# virsh dumpxml r5b2-mySQL01
<domain type='kvm' id='13'>
<name>r5b2-mySQL01</name>
<uuid>4a4c59a7ee3fc78196e4288f2862f011</uuid>
<bootloader>/usr/bin/pygrub</bootloader>
<os>
<type>linux</type>
<kernel>/var/lib/libvirt/vmlinuz.2dgnU_</kernel>
<initrd>/var/lib/libvirt/initrd.UQafMw</initrd>
<cmdline>ro root=/dev/VolGroup00/LogVol00 rhgb quiet</cmdline>
</os>
<memory>512000</memory>
<vcpu>1</vcpu>
<on_poweroff>destroy</on_poweroff>
<on_reboot>restart</on_reboot>
<on_crash>restart</on_crash>
<devices>
<interface type='bridge'>
<source bridge='br0'/>
<mac address='00:16:3e:49:1d:11'/>
<script path='bridge'/>
</interface>
<graphics type='vnc' port='5900'/>
<console tty='/dev/pts/4'/>
</devices>
</domain>
# virsh create configuration_file.xml
# virsh edit softwaretesting
This opens a text editor. The default text editor is the $EDITOR shell parameter (set to vi by default).
Suspend a guest with virsh:
# virsh suspend {domain-id, domain-name or domain-uuid}
When a guest is in a suspended state, it consumes system RAM but not processor resources. Disk and network I/O does not occur while the guest is suspended. This operation is immediate and the guest can be restarted with the
resume (
Resuming a guest) option.
Restore a suspended guest with virsh using the resume option:
# virsh resume {domain-id, domain-name or domain-uuid}
This operation is immediate and the guest parameters are preserved for suspend and resume operations.
Save the current state of a guest to a file using the virsh command:
# virsh save {domain-name, domain-id or domain-uuid} filename
This stops the guest you specify and saves the data to a file, which may take some time given the amount of memory in use by your guest. You can restore the state of the guest with the
restore (
Restore a guest) option. Save is similar to pause, instead of just pausing a guest the present state of the guest is saved.
# virsh restore filename
This restarts the saved guest, which may take some time. The guest's name and UUID are preserved but are allocated for a new id.
Shut down a guest using the virsh command:
# virsh shutdown {domain-id, domain-name or domain-uuid}
You can control the behavior of the rebooting guest by modifying the on_shutdown parameter in the guest's configuration file.
Reboot a guest using virsh command:
#virsh reboot {domain-id, domain-name or domain-uuid}
You can control the behavior of the rebooting guest by modifying the on_reboot element in the guest's configuration file.
Force a guest to stop with the virsh command:
# virsh destroy {domain-id, domain-name or domain-uuid}
This command does an immediate ungraceful shutdown and stops the specified guest. Using
virsh destroy can corrupt guest file systems . Use the
destroy option only when the guest is unresponsive. For para-virtualized guests, use the
shutdown option(
Shut down a guest) instead.
To get the domain ID of a guest:
# virsh domid {domain-name or domain-uuid}
To get the domain name of a guest:
# virsh domname {domain-id or domain-uuid}
To get the Universally Unique Identifier (UUID) for a guest:
# virsh domuuid {domain-id or domain-name}
An example of virsh domuuid output:
# virsh domuuid r5b2-mySQL01
4a4c59a7-ee3f-c781-96e4-288f2862f011
Using virsh with the guest's domain ID, domain name or UUID you can display information on the specified guest:
# virsh dominfo {domain-id, domain-name or domain-uuid}
This is an example of virsh dominfo output:
# virsh dominfo r5b2-mySQL01
id: 13
name: r5b2-mysql01
uuid: 4a4c59a7-ee3f-c781-96e4-288f2862f011
os type: linux
state: blocked
cpu(s): 1
cpu time: 11.0s
max memory: 512000 kb
used memory: 512000 kb
To display information about the host:
# virsh nodeinfo
An example of virsh nodeinfo output:
# virsh nodeinfo
CPU model x86_64
CPU (s) 8
CPU frequency 2895 Mhz
CPU socket(s) 2
Core(s) per socket 2
Threads per core: 2
Numa cell(s) 1
Memory size: 1046528 kb
This displays the node information and the machines that support the virtualization process.
To display the guest list and their current states with virsh:
# virsh list
Other options available include:
the --inactive option to list inactive guests (that is, guests that have been defined but are not currently active), and
the --all option lists all guests. For example:
# virsh list --all
Id Name State
----------------------------------
0 Domain-0 running
1 Domain202 paused
2 Domain010 inactive
3 Domain9600 crashed
The output from virsh list is categorized as one of the six states (listed below).
-
The running state refers to guests which are currently active on a CPU.
-
Guests listed as blocked are blocked, and are not running or runnable. This is caused by a guest waiting on I/O (a traditional wait state) or guests in a sleep mode.
-
The paused state lists domains that are paused. This occurs if an administrator uses the pause button in virt-manager, xm pause or virsh suspend. When a guest is paused it consumes memory and other resources but it is ineligible for scheduling and CPU resources from the hypervisor.
-
The shutdown state is for guests in the process of shutting down. The guest is sent a shutdown signal and should be in the process of stopping its operations gracefully. This may not work with all guest operating systems; some operating systems do not respond to these signals.
-
Domains in the dying state are in is in process of dying, which is a state where the domain has not completely shut-down or crashed.
-
crashed guests have failed while running and are no longer running. This state can only occur if the guest has been configured not to restart on crash.
To display virtual CPU information from a guest with virsh:
# virsh vcpuinfo {domain-id, domain-name or domain-uuid}
An example of virsh vcpuinfo output:
# virsh vcpuinfo r5b2-mySQL01
VCPU: 0
CPU: 0
State: blocked
CPU time: 0.0s
CPU Affinity: yy
To configure the affinity of virtual CPUs with physical CPUs:
# virsh vcpupin domain-id vcpu cpulist
The domain-id parameter is the guest's ID number or name.
The vcpu parameter denotes the number of virtualized CPUs allocated to the guest.The vcpu parameter must be provided.
The cpulist parameter is a list of physical CPU identifier numbers separated by commas. The cpulist parameter determines which physical CPUs the VCPUs can run on.
To modify the number of CPUs assigned to a guest with virsh:
# virsh setvcpus {domain-name, domain-id or domain-uuid} count
The new count value cannot exceed the count above the amount specified when the guest was created.
To modify a guest's memory allocation with virsh :
# virsh setmem {domain-id or domain-name} count
You must specify the count in kilobytes. The new count value cannot exceed the amount you specified when you created the guest. Values lower than 64 MB are unlikely to work with most guest operating systems. A higher maximum memory value does not affect an active guests. If the new value is lower the available memory will shrink and the guest may crash.
Use virsh domblkstat to display block device statistics for a running guest.
# virsh domblkstat GuestName block-device
Use virsh domifstat to display network interface statistics for a running guest.
# virsh domifstat GuestName interface-device
A guest can be migrated to another host with virsh. Migrate domain to another host. Add --live for live migration. The migrate command accepts parameters in the following format:
# virsh migrate --live GuestName DestinationURL
The --live parameter is optional. Add the --live parameter for live migrations.
The GuestName parameter represents the name of the guest which you want to migrate.
The DestinationURL parameter is the URL or hostname of the destination system. The destination system requires:
Once the command is entered you will be prompted for the root password of the destination system.
This section covers managing virtual networks with the virsh command. To list virtual networks:
# virsh net-list
This command generates output similar to:
# virsh net-list
Name State Autostart
-----------------------------------------
default active yes
vnet1 active yes
vnet2 active yes
To view network information for a specific virtual network:
# virsh net-dumpxml NetworkName
This displays information about a specified virtual network in XML format:
# virsh net-dumpxml vnet1
<network>
<name>vnet1</name>
<uuid>98361b46-1581-acb7-1643-85a412626e70</uuid>
<forward dev='eth0'/>
<bridge name='vnet0' stp='on' forwardDelay='0' />
<ip address='192.168.100.1' netmask='255.255.255.0'>
<dhcp>
<range start='192.168.100.128' end='192.168.100.254' />
</dhcp>
</ip>
</network>
Other virsh commands used in managing virtual networks are:
-
virsh net-autostart network-name — Autostart a network specified as network-name.
-
virsh net-create XMLfile — generates and starts a new network using an existing XML file.
-
virsh net-define XMLfile — generates a new network device from an existing XML file without starting it.
-
virsh net-destroy network-name — destroy a network specified as network-name.
-
virsh net-name networkUUID — convert a specified networkUUID to a network name.
-
virsh net-uuid network-name — convert a specified network-name to a network UUID.
-
virsh net-start nameOfInactiveNetwork — starts an inactive network.
-
virsh net-undefine nameOfInactiveNetwork — removes the definition of an inactive network.
