Snapshot XML format

Snapshot XML

Attributes of libvirt snapshots are stored as child elements of the domainsnapshot element. At snapshot creation time, normally only the name and description elements are settable; the rest of the fields are ignored on creation, and will be filled in by libvirt in for informational purposes by virDomainSnapshotGetXMLDesc(). However, when redefining a snapshot (since 0.9.5), with the VIR_DOMAIN_SNAPSHOT_CREATE_REDEFINE flag of virDomainSnapshotCreateXML(), all of the XML described here is relevant.

Snapshots are maintained in a hierarchy. A domain can have a current snapshot, which is the most recent snapshot compared to the current state of the domain (although a domain might have snapshots without a current snapshot, if snapshots have been deleted in the meantime). Creating or reverting to a snapshot sets that snapshot as current, and the prior current snapshot is the parent of the new snapshot. Branches in the hierarchy can be formed by reverting to a snapshot with a child, then creating another snapshot.

The top-level domainsnapshot element may contain the following elements:

name

The name for this snapshot. If the name is specified when initially creating the snapshot, then the snapshot will have that particular name. If the name is omitted when initially creating the snapshot, then libvirt will make up a name for the snapshot, based on the time when it was created.

description

A human-readable description of the snapshot. If the description is omitted when initially creating the snapshot, then this field will be empty.

creationTime

The time this snapshot was created. The time is specified in seconds since the Epoch, UTC (i.e. Unix time). Readonly.

state

The state of the domain at the time this snapshot was taken. When the domain is reverted to this snapshot, the domain's state will default to whatever is in this field. Readonly.

parent

The parent of this snapshot. This element contains exactly one child element, name. This specifies the name of the parent snapshot of this snapshot, and is used to represent trees of snapshots, as described above. Readonly.

domain

The domain that this snapshot was taken against. Older versions of libvirt stored only a single child element, uuid; reverting to a snapshot like this is risky if the current state of the domain differs from the state that the domain was created in, and requires the use of the VIR_DOMAIN_SNAPSHOT_REVERT_FORCE flag in virDomainRevertToSnapshot(). Newer versions of libvirt store the entire inactive domain configuration at the time of the snapshot (since 0.9.5). Readonly.

Examples

Using this XML on creation:

<domainsnapshot>
  <description>Snapshot of OS install and updates</description>
</domainsnapshot>

will result in XML similar to this from virDomainSnapshotGetXMLDesc:

<domainsnapshot>
  <name>1270477159</name>
  <description>Snapshot of OS install and updates</description>
  <state>running</state>
  <creationTime>1270477159</creationTime>
  <parent>
    <name>bare-os-install</name>
  </parent>
  <domain>
    <name>fedora</name>
    <uuid>93a5c045-6457-2c09-e56c-927cdf34e178</uuid>
    <memory>1048576</memory>
    ...
    </devices>
  </domain>
</domainsnapshot>