Add these options to /etc/default/grub in Proxmox to provide a TTY to the virtual serial port of ILO of an HP Prolian Gen 8. The graphical terminal can still be used in the web view and via cable.

GRUB_CMDLINE_LINUX_DEFAULT="console=ttyS1,9600n8 console=tty0"
GRUB_TERMINAL_INPUT="console serial"
GRUB_TERMINAL_OUTPUT="gfxterm serial"
GRUB_SERIAL_COMMAND="serial --unit=1 --speed=9600 --word=8 --parity=no --stop=1"

* https://docs.kernel.org/admin-guide/serial-console.html

Access VSP:

[clerie@krypton:~]$ ssh 10.10.10.10 -o "Kexalgorithms diffie-hellman-group14-sha1" -o "Hostkeyalgorithms ssh-rsa" -l Administrator
Administrator@10.10.10.10's password: 
User:Administrator logged-in to 10.10.10.10

iLO Advanced 2.72 at  Oct 20 2019
Server Name: host is unnamed
Server Power: On

</>hpiLO-> VSP

Virtual Serial Port Active: COM2

Starting virtual serial port.
Press 'ESC (' to return to the CLI Session.


proxmox login: