Allegedly, on or about 19 March 2018, Javier Perez sent:
My question is: How can I restart the Xorg server and/or the nouveau driver?
Next time you're logged in and things are working, go into the keyboard preferences, and delve through the keyboard layout options. There's a hotkey, that's traditionally CTRL+ALT+BACKSPACE to restart X, but has been disabled by default, for quite some time. It's one of the first things I re-enable on new systems.
If remotely logging into a stalled system, run the "top" command and find Xorg, you could try killing it. I used to do something like switch to runlevel 3 (command line only), wait for that to complete, then switch back to runlevel 5 (GUI). There's probably other ways, too.