Do regular VM snapshots trigger fsfreeze via guest agent?

[PHPMaroc]

Hi everyone,

When taking a regular VM snapshot in Proxmox (either from the web GUI or via CLI), and the QEMU Guest Agent is installed and running inside the VM — does Proxmox automatically trigger a fsfreeze (filesystem freeze) via the guest agent?

I’m asking because I do not want the guest filesystem to be frozen during snapshots, as it sometimes interferes with applications running in the VM.

If fsfreeze is triggered by default, is there a way to disable it while still having the guest agent enabled for other features?

Thanks a lot for your help!

 

[Impact]

Yes it does. You can monitor it via journalctl -fu qemu-guest-agent.service and then do a snapshot to see.
I don't recommend it but you can disable the freezing via Options > QEMU Guest Agent. What issues do you encounter?

 

[PHPMaroc]

Thanks for your reply!

My question is about the option in the VM settings:
"Freeze/thaw guest filesystems on backup for consistency" — it specifically mentions "on backup".

Does this also apply to regular snapshots (the ones created manually or via API/CLI, not backup jobs)?
Or is fsfreeze only triggered when running a backup (e.g., vzdump)?

Thanks again for clarifying!

 

[Impact]

I was hoping you use the instructions above to answer this yourself but good question. I only tested that you can see the freezing in the service logs.
I tested this with disabled freezing too now and a snapshot will still call fsreeze even if it's disabled in the options. I guess there's a reason backup was mentioned. Sorry for missing that aspect previously.
Perhaps you could create an issue on bugzilla so there's control to be had over that too.

 

[PHPMaroc]

Thanks for your clarification!

Currently, I'm using the automatic snapshot tool proxmox-autosnap, and it works well overall.
However, with hourly snapshots, the fsfreeze causes issues inside some Windows VMs — especially at the moment the snapshot is taken — and sometimes it takes longer than expected.

I'm now considering switching to native ZFS snapshots directly, instead of using this tool which relies on Proxmox's built-in snapshot command.

What do you think? Would this approach avoid the guest agent freeze and give me more control?

Thanks!