Well, @runlinux.run, I stand corrected. It used to work fairly easy, but not any more, or at least it’s not working in UB server. It would appear one needs an Xserver running, and that’s just a non-starter for me on a server. Even their documentation says is should work: Guest Additions
So, sorry for the mis-lead on that one. I guess the next best option is just to use SSH.