To unlock a locked Xubuntu Linux workstation, you can use ‘sudo loginctl unlock-sessions’ and alt-ctrl-F7. This command works over SSH and over Salt, but obviously it requires root access to target computer.
With salt:
$ sudo salt teroscomputer cmd.run 'loginctl unlock-sessions'
With SSH:
$ ssh tero@teroscomputer $ sudo loginctl unlock-sessions
On the target computer, press alt-ctrl-F7 (alt-ctrl-F8…).
You are now on unlocked desktop. Well done. Always keep using good passwords.
Q: Is this a bug/vulnerability? No, by design you can do anything when you have root access.
Thanks to Fincer for the tip for this command.
Updated: fixed styling.