Verbose boot with GRUB
Unfortunately, Proxmox VE ships with quiet booting, the screen goes blank and then turns into login prompt. It does not use e.g. Plymouth that would allow you to optionally see the boot messages, but save on the boot-up time when they are not needed. While trivial, there does not seem to be dedicated official guide on this basic troubleshooting tip.
Note
There is only one exception to the statement above - ZFS install on non-SecureBoot UEFI system, in which case the bootloader is systemd-boot instead, which defaults to verbose boot. You may wish to replace it with GRUB instead, however.
One-off verbose boot
Instantly after power-on, when presented with GRUB
boot menu, press e to edit the commands of the selected boot option:
Navigate onto the linux line and note the quiet keyword at the end:
Remove the quiet keyword leaving everything else intact:
Press F10 to proceed to boot verbosely.
Permanent verbose boot
You may want to have verbose setup as your default, it only adds a couple of seconds to your boot-up time.
On a working booted-up system, edit /etc/default/grub:
nano /etc/default/grub
Remove the quiet keyword, so that the line looks like this:
GRUB_CMDLINE_LINUX_DEFAULT=""Save your changed file and apply the changes:
update-grubIn case of ZFS install, you might be instead using e.g. Proxmox boot tool:
proxmox-boot-tool refreshUpon next reboot, you will be greeted with verbose output.