qm "commit changes" question/behavior (noob head-scratching thing)

ronejamesdo

Member
Apr 22, 2024
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I ran this:

qm set 114 --scsi1 [storage-name]:101/vm-101-disk-1.qcow2,backup=0

Which made a visible change on the web interface in that a second line appeared below the original hard disk configuration line (the original hard disk configuration has the "Backup" box checked by default). That line was "yellow", included the backup=0 and if I clicked the drive there it had a "Revert" button. (It also didn't work, in the sense that if I take a backup it backs up that drive too.)

1748957551364.png

Nothing I could find (command line wise) would actually apply those changes although this:

https://pve.proxmox.com/pve-docs/qm.1.html

seemed to indicate that it would just work "...better to use the qm command... instantaneously apply most changes to running VM... no need to restart the VM".

Eventually I did vm stop and vm start on that VM. That committed the changes. BUT that also makes further changes not need the stop/start. If I run the same command and set "backup=1" it changes immediately in the web interface (no yellow line, no stop and start), and I can toggle it back and forth from 0 to 1 repeatedly now.

Why? (IE - What becomes different after the one stop/start that allows the instant apply changes, and can anything take that away again, like another reboot for example?)

Thanks.


Just for background (since someone might wonder why I care):

I am looking for a way to take two separate backups of a Proxmox virtual machine (I do not have Proxmox Backup Server, this would just use mounted storage from Proxmox itself).

In one of the backups I want the whole machine.
In the other I want the whole machine, minus one of the hard disks (the storage part of the server, with user-made changes).

(One backup is for "the whole thing crashed, I just need it back" and the other is for "this is an OS issue, I want the OS back, pre-event, but I want all of the server's files current till the moment it I start restoration".)

I have not found a way to do this yet but the idea that got me to this thread was that perhaps I could script/cron "backup=0/backup=1" changes to the disk (timed for when I want each kind of backup).
 
Why? (IE - What becomes different after the one stop/start that allows the instant apply changes, and can anything take that away again, like another reboot for example?)
The command you ran also unset the option iothread. Meaning the default would apply again, and the default is to turn it off. Turning that feature on and off requires a VM restart. Hence, your changes did not apply immediately.