Backup job causes PVE to machine to reboot

[promoxer]

vzdump 102 103 --node pve --all 0 --mailnotification always --mailto email@example.com --mode snapshot --compress zstd --fleecing 0 --prune-backups 'keep-last=1' --notes-template '{{guestname}}' --storage local

1. Starting from a few days ago, I'm waking up to a rebooted PVE
2. I eventually and traced it down to the VMs backup job and reproduced the problem
3. The job runs 2am daily and reboots at around 3-4am (I'm notified each time PVE boots successfully)
3. And it was basically like pressing the reset button on the hardware, not a controlled reboot, where the VMs shutdown etc
4. I can accept a failed backup job, but a reboot feels wrong
5. In a matter that I suspect is related, my local storage is almost full
6. How can I track down what is causing PVE to suddenly reboot?

 

[Onslow]

From your post I guess that you've already checked the logs and they don't contain a hint.
As you suspect that a lack of free local storage may be the cause, you can write a script which in a loop logs to a file the amount of free space and possibly which directory consumes how much. Then from cron start this script before the backup starts.
Even if there's an unclean reboot, the resulting log should contain some data.