How to Create KVM Virtual Machine 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 we can say snapshot keeps or preserve the state and data of a virtual machine at given point of time.

Where we can use VM snapshots ..?

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 (domain) Snapshot

I am assuming KVM hypervisor is already configured on CentOS 7 / RHEL 7 box and VMs are running on it. We can list the all the VMs on hypervisor using below virsh command,

[[email protected] ~]# 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
[[email protected] ~]#

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”

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

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

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

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

[[email protected] ~]# 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
[[email protected] ~]#

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

[[email protected] ~]# 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}

[[email protected] ~]# virsh snapshot-revert webserver webserver_snap
[[email protected] ~]#

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:

[[email protected] ~]# virsh snapshot-list --domain webserver
 Name                 Creation Time             State
 webserver_snap       2018-02-04 15:05:05 +0530 running
[[email protected] ~]#
[[email protected] ~]# virsh snapshot-delete --domain webserver --snapshotname webserver_snap
Domain snapshot webserver_snap deleted
[[email protected] ~]#

That’s all from this article, I hope you guys get an idea on how to manage KVM virtual machine snapshots using virsh command. Please do share your feedback and don’t hesitate to share it among your technical friends 🙂

5 thoughts on “How to Create KVM Virtual Machine Snapshot with virsh command”

  1. Question:
    Lets say you have 3 snapshots, A B and C, taken in that order (thats C taken after B taken after A) with C as the current snapshot. If I want to delete the snapshots A and B, will the command still work. If yes, do you see potential problems of doing these?

  2. Not able to merge snapshot to existing disk

    **KVM and qemu RPM info :-**
    [[email protected]_rhel ~]# rpm -qa | grep -i qemu

    [[email protected]_rhel ~]# virsh snapshot-list –domain centos7.0
    Name Creation Time State
    testVM2-firstSNAP35 2019-08-08 13:22:11 -0400 shutoff
    testVM2-firstSNAP36 2019-08-08 13:24:48 -0400 shutoff
    testVM2-firstSNAP37 2019-08-08 13:27:13 -0400 shutoff

    [[email protected]_rhel ~]# virsh snapshot-info –domain centos7.0 –snapshotname testVM2-firstSNAP37
    Name: testVM2-firstSNAP37
    Domain: centos7.0
    Current: yes
    State: shutoff
    Location: external
    Parent: –
    Children: 0
    Descendants: 0
    Metadata: yes

    **if VM is shutdown :-**

    [[email protected]_rhel ~]# virsh blockcommit centos7.0 vda –active –verbose –pivot
    error: Requested operation is not valid: domain is not running

    **if VM is Running :-**
    [[email protected]_rhel ~]# virsh blockcommit centos7.0 vda –active –verbose –pivot
    error: unsupported configuration: online commit not supported with this QEMU binary

    1. QEMU libraries are old that’s why online commit is not possible in your current qemu library, You need to install QEMU 2.1 ( and above), libvirt-1.2.9 (and above)

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