Bug#681830: #681830 - gdm3: X failures not necessarily related to gnome-shell also cause this

[Tony Houghton]

I've seen this behaviour several times, and agree it's at least
"serious", so sorry for not reporting this or finding a bug to subscribe
to earlier. Today it was caused by X failing to start due to some
problem I couldn't be bothered to remmebr after deleting several hundred
files from /var/log, but involved "No usable screen configurations
found" or something along those lines. I think I've seen it caused by
something as common-place as trying to use the proprietary nvidia driver
without a matching kernel module.

Whatever is causing X to die but leave processes behind, gdm3 should not
allow this. I remember previous versions showing messages like "X server
respawning too fast, shutting down", but it seems like gdm3 (still) can't
properly protect against this despite what the changelog says in closing
#650183.

I'm currently using gdm3 3.4.1-5.