Ubuntu – Gnome3 Freezing / Hanging / Unresponsive – can’t restart

16.04gnomekeyboardmousemultiseat

I am running UbuntuGNOME 16.04. The Gnome3 interface is useful because of its touch support (helpful for various peripherals, as this is a desktop), but it hangs every so often – usually with specific programs (Firefox with a number of tabs open, Virtual Box running a CAD program on Windows 7 x64 Ultimate, etc).

The mouse responds to moving around the screen, but doesn't accept other inputs (no clicks, and it keeps the state it was in – e.g. a 'move cross', a waiting icon, etc). The keyboard doesn't accept ANY inputs.

I have tried ALT+F2–>R–>ENTER, Ctrl+Alt+F1, Ctl+Alt+F2 (or F3, etc). Nothing works, as the keyboard is 'unresponsive'

HOWEVER … this is a multiseat (2, to be precise) system. The other seat is responsive.

Q1: How do I overcome the keyboard not being responsive?

Q2: Can I restart the Gnome instance in Seat1 from Seat2?

THANKS!