How to Create KVM Virtual Machine Snapshot with Virsh Command

In this blog post, we will explain how to create KVM virtual machine (vm) snapshot with virsh command.

While working on the virtualization platform system administrators usually take the snapshot of virtual machine before doing any major activity like deploying the latest patch and code.

Virtual machine snapshot is a copy of virtual machine’s disk at the specific point of time. In other words, snapshots are like frozen moments in time, capturing the state of a virtual machine at a particular point.

Why VM Snapshots Matter?

If you are working on KVM based hypervisors we can take virtual machines or domain snapshot using the virsh command. Snapshot becomes very helpful in a situation where you have installed or apply the latest patches on the VM but due to some reasons, application hosted in the VMs becomes unstable and application team wants to revert all the changes or patches. If you had taken the snapshot of the VM before applying patches then we can restore or revert the VM to its previous state using snapshot.

Note: We can only take the snapshot of the VMs whose disk format is Qcow2 and raw disk format is not supported by kvm virsh command, Use below command to convert the raw disk format to qcow2

# qemu-img convert -f raw -O qcow2 image-name.img image-name.qcow2

Create KVM Virtual Machine Snapshot

We are assuming KVM hypervisor is already configured on RHEL 8/9 or Rocky Linux or Ubuntu and VMs are running on it. We can list the all the VMs on hypervisor using below virsh command,

# virsh list --all
 Id    Name                           State
----------------------------------------------------
 94    centos7.0                      running
 101   overcloud-controller           running
 102   overcloud-compute2             running
 103   overcloud-compute1             running
 114   webserver                      running
 115   Test-MTN                       running
#

Let’s suppose we want to create the snapshot of ‘webserver‘ VM, run the below command,

Syntax:

# virsh snapshot-create-as –domain {vm_name} –name {snapshot_name} –description  “enter description here”

# virsh snapshot-create-as --domain webserver --name webserver_snap --description "snap before patch on 4Feb2018"
Domain snapshot webserver_snap created
#

Once the snapshot is created then we can list snapshots related to the VM using beneath command,

# virsh snapshot-list webserver
 Name                 Creation Time             State
------------------------------------------------------------
 webserver_snap       2018-02-04 15:05:05 +0530 running
#

To list the detailed info of VM’s snapshot, run the beneath virsh command,

# virsh snapshot-info --domain webserver --snapshotname webserver_snap
Name:           webserver_snap
Domain:         webserver
Current:        yes
State:          running
Location:       internal
Parent:         -
Children:       0
Descendants:    0
Metadata:       yes
#

We can view the size of snapshot using below qemu-img command,

# qemu-img info /var/lib/libvirt/images/snaptestvm.img

Revert / Restore  KVM Virtual Machine to snapshot

Let’s assume we want to revert or restore webserver VM to the snapshot that we have created in above step. Use below virsh command to restore Webserver VM to its snapshot “webserver_snap”

Syntax :

# virsh snapshot-revert {vm_name} {snapshot_name}

# virsh snapshot-revert webserver webserver_snap

Delete KVM Virtual Machine Snapshots

To delete KVM virtual machine snapshots, first get the VM’s snapshot details using “virsh snapshot-list” command and then use “virsh snapshot-delete” command to delete the snapshot. Example is shown below:

# virsh snapshot-list --domain webserver
 Name                 Creation Time             State
------------------------------------------------------------
 webserver_snap       2018-02-04 15:05:05 +0530 running
#

# virsh snapshot-delete --domain webserver --snapshotname webserver_snap
Domain snapshot webserver_snap deleted
#

Conclusion:

Creating KVM virtual machine snapshots with the Virsh command provides an essential layer of flexibility and security when working with virtualization. Snapshots allow you to experiment, troubleshoot, and maintain system stability effortlessly. By following the steps in this guide, you can harness the power of KVM snapshots to take control of your virtual machines, ensuring your work is safe, efficient, and well-managed.

Also Read : How to Create and Manage KVM Virtual Machines via Command Line