When X decides to crash
Yesterday evening at 20:45 (UTC+1) I decide to do a good deed and help Mamarok help a Kubuntu user getting his system fixed.
The symptoms sound quite familiar (apparently there also have been quite some cases of this): login doesn't work, get thrown back to KDM.
At approximately 21:00 I realized that simply helping to help will not suffice in this particular case.
At 22:36 I gained SSH access to the affected machine.
At 00:43 I found the source of the issue.
At 01:17 I got all data for a somewhat feasible bug report.
I certainly do hope that you now wonder what the problem was I spent around 4 hours of time on. Well, an X crash, though you probably guessed that much already from the title of this post
More interesting is how we got there, I collected the most important data in the bug report on launchpad.
Apparently some recent update triggered the issue. Naturally I inspected the dpkg.log, but since there was one rather large update recently, that did not give me much of a clue, xsession-errors is also rather unspectacular, well, other than the X connection problems (I suspect those were caused by X going down?).