How to get OS version of proxmox server over command line (cli)?

How do I check what version of Proxmox my server is running?

Wikipedia tells me that Proxmox runs on a modified version of Ubuntu LTS

It is a Debian-based Linux distribution with a modified Ubuntu LTS kernel

But when I check /etc/issue as expected with a Debian-based release, I see only this:

host:~# cat /etc/issue

------------------------------------------------------------------------------

Welcome to the Proxmox Virtual Environment. Please use your web browser to
configure this server - connect to:

  https://192.168.0.5/

------------------------------------------------------------------------------

host:~#

How do I actually determine the OS version of my proxmox server using the command-line?

You can get the version of proxmox using the pveversion command.

host:~# pveversion
pve-manager/6.2-6/ee1d7754 (running kernel: 5.4.41-1-pve)
host:~# 

For even more information, use the --verbose flag

pveversion --verbose