My home lab has an NFS server for storage and a proxmox hypervisor connecting to it. If the power ever goes out for more than my UPS can handle, startup is a bit of a mess. My ProxMox server boots up much faster than my NFS server, so the result is no VMs start automatically (due to storage being unavailable) and I have to manually go in and start everything.
I found this bug report from 2015 which frustratingly doesn’t appear to have any traction to it. Ideally I could just tell the first VM to wait 5 minutes before turning on, and then trigger all the other VMs to turn on once the first one is up, but the devs don’t seem to want to address that issue. So, I got creative.
My solution was to alter the grub menu timeout before booting ProxMox. Simple but effective.
Edit /etc/default/grub and modify GRUB_TIMEOUT
#modify GRUB_TIMEOUT to your liking GRUB_TIMEOUT=300
Then simply run update-grub
Now my proxmox server waits 5 minutes before even booting the OS, by which time the NAS should be up and running. No more manual turning on of VMs after a power outage.