qm: vmgenid: fix spacing and reword,

[pve-docs.git] / qm.adoc

diff --git a/qm.adoc b/qm.adoc
index 1451f5df14d2f157f7be2044a400b36eb334ae07..bd10ca1e3c349671006cf5a1e20949da0d2bea7e 100644 (file)
--- a/qm.adoc
+++ b/qm.adoc
@@ -788,6 +788,42 @@ NOTE: It is not possible to start templates, because this would modify
 the disk images. If you want to change the template, create a linked
 clone and modify that.
 
+VM Generation ID
+----------------
+
+{pve} supports Virtual Machine Generation ID ('vmgedid') footnote:[Official
+'vmgenid' Specification
+https://docs.microsoft.com/en-us/windows/desktop/hyperv_v2/virtual-machine-generation-identifier]
+for virtual machines.
+This can be used by the guest operating system to detect any event resulting
+in a time shift event, for example, restoring a backup or a snapshot rollback.
+
+When creating new VMs, a 'vmgenid' will be automatically generated and saved
+in its configuration file.
+
+To create and add a 'vmgenid' to an already existing VM one can pass the
+special value `1' to let {pve} autogenerate one or manually set the 'UUID'
+footnote:[Online GUID generator http://guid.one/] by using it as value,
+e.g.:
+
+----
+ qm set VMID -vmgenid 1
+ qm set VMID -vmgenid 00000000-0000-0000-0000-000000000000
+----
+
+In the rare case the 'vmgenid' mechanism is not wanted one can pass `0' for
+its value on VM creation, or retroactively delete the property in the
+configuration with:
+
+----
+ qm set VMID -delete vmgenid
+----
+
+The most prominent use case for 'vmgenid' are newer Microsoft Windows
+operating systems, which use it to avoid problems in time sensitive or
+replicate services (e.g., databases, domain controller) on snapshot
+rollback, backup restore or a whole VM clone operation.
+
 Importing Virtual Machines and disk images
 ------------------------------------------