KVM Snapshots with virsh: Create and Revert

A snapshot records a VM's disk (and optionally memory) at a point in time so you can roll back after a bad update or failed experiment. This guide covers KVM snapshots with virsh, the two snapshot styles and the mistakes to avoid.

Before you start

A KVM host with libvirt and root access.
For internal snapshots the VM disk must be qcow2. See qcow2 vs raw.
Optional: qemu-guest-agent installed and running in the guest.

Internal vs external snapshots

	Internal	External
Stored	Inside the same qcow2 file	New overlay file; original becomes read-only
Revert with virsh	Simple	Supported in newer libvirt; older versions need manual steps
Use	Quick rollback points	Live backups, block commit

Create a snapshot

Internal snapshot with a description:

virsh snapshot-create-as web01 pre-upgrade --description "Before PHP upgrade"

Disk-only external snapshot, quiesced through the guest agent so filesystems are consistent:

virsh snapshot-create-as web01 backup1 --disk-only --atomic --quiesce

List and inspect snapshots

virsh snapshot-list web01 --tree

virsh snapshot-info web01 pre-upgrade

Revert to a snapshot

virsh snapshot-revert web01 pre-upgrade

Everything written after the snapshot is lost. Shut the VM down first if the snapshot did not include memory.

Delete a snapshot

virsh snapshot-delete web01 pre-upgrade

For external snapshots, merge the overlay back into the base when done, then remove metadata:

virsh blockcommit web01 vda --active --pivot --verbose

Snapshots are not backups

They live on the same storage as the VM; a disk failure loses both.
Long snapshot chains slow I/O and use more space over time.
Keep snapshots for hours or days, and take real off-host backups. See website backups explained.

Troubleshooting

"internal snapshots of a raw disk are not supported": use an external snapshot or convert to qcow2.
--quiesce fails: install and start qemu-guest-agent and add the guest agent channel to the VM.
Host disk filling up: delete or commit old snapshots.

Frequently asked questions

Can I snapshot my VPS from a panel?

Many VPS panels offer snapshots or backups; options depend on the provider. Virtualizor users can see Virtualizor backups.

Do snapshots include RAM?

Internal snapshots of a running VM include memory state by default; --disk-only snapshots do not.

How many snapshots should I keep?

As few as possible, ideally one or two short-lived ones.

Next steps

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