Basic operations to manage a KVM virtual machine
Today we will see basic operations to manage a KVM virtual machine.
Information and requirements
These elements are to be taken into consideration to follow this article:
- You have installed KVM, QEMU and Libvirt as described here.
- You have created a KVM virtual machine template as described here.
State
Save virtual machine state
This command stops the virtual machine mail.illuad.local and saves the data to a file called state-mail.illuad.local. This will take a few moments depending upon the amount of memory in use by your virtual machine.
sudo virsh save mail.illuad.local state-mail.illuad.local
Domain mail.illuad.local saved to state-mail.illuad.local
Restore virtual machine state
To restore the previously saved state of a virtual machine, just specify the file name like this.
sudo virsh restore state-mail.illuad.local
Domain restored from state-mail.illuad.local
Power management
Suspend or pause
sudo virsh suspend mail.illuad.local
Domain 'mail.illuad.local' suspended
Resume
sudo virsh resume mail.illuad.local
Domain 'mail.illuad.local' resumed
Stop active virtual machines
To forcibly stop an active virtual machine, and leave it in the inactive state, execute this command.
sudo virsh destroy mail.illuad.local
Domain 'mail.illuad.local' destroyed
You can also gracefully stop the virtual machine instead of forcing it.
sudo virsh destroy mail.illuad.local --graceful
Domain 'mail.illuad.local' destroyed
Snapshot
Create
I don’t describe the use of a snapshot, but I do advise you to do one at the beginning. First, shutdown your virtual machine.
sudo virsh shutdown mail.illuad.local
Then, you can create it.
sudo virsh snapshot-create-as --domain mail.illuad.local --name "Start" --description "Virutal machine initial state"
Domain snapshot Start created
You can list snapshots like this.
sudo virsh snapshot-list mail.illuad.local
Name Creation Time State
----------------------------------------------
Start 2021-06-03 00:40:14 +0200 shutoff
Restore
sudo virsh shutdown mail.illuad.local
sudo virsh snapshot-revert --domain mail.illuad.local --snapshotname Start
Delete
sudo virsh snapshot-delete --domain mail.illuad.local --snapshotname Start
Domain snapshot Start deleted
Network
Retrieve virtual interfaces
sudo virsh domiflist mail.illuad.local
Interface Type Source Model MAC
-------------------------------------------------------------
vnet0 network default virtio 52:54:00:81:61:4e
Retrieve IP address(es)
sudo virsh domifaddr mail.illuad.local
Name MAC address Protocol Address
-------------------------------------------------------------------------------
vnet0 52:54:00:81:61:4e ipv4 192.168.122.238/24
Retrieve network interface stats
The virtual interface’s name of my virtual machine is vnet0, replace it by yours.
sudo virsh domifstat mail.illuad.local vnet0
vnet0 rx_bytes 11214
vnet0 rx_packets 181
vnet0 rx_errs 0
vnet0 rx_drop 0
vnet0 tx_bytes 4160
vnet0 tx_packets 49
vnet0 tx_errs 0
vnet0 tx_drop 0
Cleaning
Remove a virtual machine and delete its storage
Make sure your virtual machine is shutdown, otherwise you’ll have the following message.
error: Storage volume deletion is supported only on stopped domains
Make sure no snapshot belongs to your virtual machine, otherwise you’ll have the following message.
error: Requested operation is not valid: cannot delete inactive domain with 1 snapshots
sudo virsh undefine mail.illuad.local --remove-all-storage
Domain 'mail.illuad.local' has been undefined
Volume 'vda'(/var/lib/libvirt/images/mail.illuad.local.qcow2) removed.
General
Virtual machine information
sudo virsh dominfo mail.illuad.local
Id: 1
Name: mail.illuad.local
UUID: c712dfc7-fd1a-497c-b49e-4f45b0b58273
OS Type: hvm
State: running
CPU(s): 4
CPU time: 46.0s
Max memory: 4194304 KiB
Used memory: 4194304 KiB
Persistent: yes
Autostart: disable
Managed save: no
Security model: none
Security DOI: 0
Dump virtual machine’s XML configuration
This command will display the complete configuration details (software and hardware) of the virtual machine.
sudo virsh dumpxml mail.illuad.local
<domain type='kvm' id='1'>
<name>mail.illuad.local</name>
<uuid>c712dfc7-fd1a-497c-b49e-4f45b0b58273</uuid>
<metadata>
[...]
Libguestfs
You need the libguestfs tools installed to execute those commands.
Read file content
You can as well cat a file without doing SSH to the virtual machine or accessing it via the console.
sudo virt-cat --domain mail.illuad.local /etc/redhat-release
Rocky Linux release 8.4 (Green Obsidian)
Edit a file
Using virt-edit on live virtual machines, or concurrently with other disk editing tools, can be dangerous, potentially causing disk corruption. The virtual machine must be shut down before you use this command, and disk images must not be edited concurrently.
sudo virt-edit --domain mail.illuad.local /etc/hosts
Display virtual machine disk usage
sudo virt-df --domain mail.illuad.local
Filesystem 1K-blocks Used Available Use%
mail.illuad.local:/dev/sda1 1038336 138160 900176 14%
mail.illuad.local:/dev/cl/root 17811456 1410328 16401128 8%
List filesystems, partitions, block devices, LVM in a virtual machine
sudo virt-filesystems --all --uuid --human-readable --long --domain mail.illuad.local
Name Type VFS Label MBR Size Parent UUID
/dev/sda1 filesystem xfs - - 1014M - 1ea2d7be-bfbb-4d61-90e2-ef8baee369ee
/dev/cl/root filesystem xfs - - 17G - 5106b919-2692-4e50-9040-251795b68913
/dev/cl/swap filesystem swap - - 2.0G - 46cc4821-647b-4d83-8b62-4285b54ad56b
/dev/cl/root lv - - - 17G /dev/cl HF2PvO-ecs6-W7ds-zENe-aK5t-Cqrz-MRJ1Kt
/dev/cl/swap lv - - - 2.0G /dev/cl 0YaYHy-aaEw-kTLM-sza1-CkDI-m66s-hqSdpR
/dev/cl vg - - - 19G /dev/sda2 IoAFjZc5FuYYbmOERrJEX47bRL2JvmuZ
/dev/sda2 pv - - - 19G - LgDuy214LzfntxBDFtTPDAFaXW5TB1Ii
/dev/sda1 partition - - 83 1.0G /dev/sda -
/dev/sda2 partition - - 8e 19G /dev/sda -
/dev/sda device - - - 20G - -
Volume and pool
List pool
The default pool name (and if you have followed my articles) is images. Otherwise, you can execute the following command to list pools.
sudo virsh pool-list
Name State Autostart
------------------------------
images active yes
sudo virsh vol-list --details --pool images
Name Path Type Capacity Allocation
------------------------------------------------------------------------------------------------------------
centos_8_stream.qcow2 /var/lib/libvirt/images/centos_8_stream.qcow2 file 20.00 GiB 2.02 GiB
mail.illuad.local.qcow2 /var/lib/libvirt/images/mail.illuad.local.qcow2 file 20.00 GiB 2.12 GiB
Remove a volume
sudo virsh vol-delete --pool images --vol mail.illuad.local.qcow2
Vol mail.illuad.local.qcow2 deleted
Refresh the pool
sudo virsh pool-refresh images
Pool images refreshed