lightDM crashes on restart after upgrading from Precise to Quantal

[bamyasi]

I have upgraded my home PC from Precise to Quantal today. The upgrade process was mostly smooth and I was able to fix a few glitches that did happen afterwards (this is not the first time I do a live Kubuntu system upgrade after all). However, one last annoying bug remains adamant to all my efforts to fix it. Every time I try to log out of the KDE session it does not work: the screen goes black and the system locks up for 30-40 seconds (even keyboard is locked), then the computer reboots. Same thing happens when I run "sudo service lightdm restart" from console. I have searched the Web and Launchpad bug reports but found nothing related to my problem. Note, this system uses nvidia-current drivers from X-Updates PPA (304.64) with GeForce GT 520 video card. Everything else works fine: desktop effects, audio, network, etc. Only the logout sequence causes a system crash and hard reboot.

Any ideas?

[SteveRiley]

Some guesses, and that's all...

1. Can you gracefully shut down the computer after LightDM starts but before you log into a KDE session?

2. If you create a new user account, and log into that one, can you then properly log out?

[bamyasi]

Some guesses, and that's all...

1. Can you gracefully shut down the computer after LightDM starts but before you log into a KDE session?

Yes.

2. If you create a new user account, and log into that one, can you then properly log out?

I haven't tried creating a new user yet but I did try with guest account (which uses default user configuration) and observed the same LightDM crash upon logout attempt.

[bamyasi]

I have done a fresh install of 12.10 on a brand new disk today. Initially, LightDM was working fine using the default open source Nvidia drivers (nouveau) and logout option on the desktop menu worked as expected. As soon as I switched to nvidia binary drivers (nvidia_current) LightDM again started crashing on me on every restart/logout attempt. So, this is obviously a software bug and not a misconfiguration due to the live upgrade, as I thought. I am just not sure where to submit my bug report: for nvidia package of for KDE/LightDM.

Interestingly enough, I am only seeing these crashes on my home computer while four other PCs I've installed at work recently are all unaffected, despite having very similar hardware and being installed using the same Kubuntu 12.10 DVD. Office computers have slightly different Nvidia cards however: GeForce GT 610 vs GT 520 in my home computer.

[SteveRiley]

Who is listed as the owning user:group of ~/.Xauthority? It should be your own user:group.

Also, could I take a look at:

~/.xsession-errors
/var/log/auth.log
/var/log/lightdm/lightdm.log
/var/log/x-0.log
/var/log/x-0-greeter.log

[bamyasi]

Who is listed as the owning user:group of ~/.Xauthority? It should be your own user:group.

Also, could I take a look at:

~/.xsession-errors
/var/log/auth.log
/var/log/lightdm/lightdm.log
/var/log/x-0.log
/var/log/x-0-greeter.log

My ~/.Xauthority file ownership & permissions look correct. I have also scanned all the above log files for errors specific to the LightDM crash but found none. There is a lot of error/warning messages, especially in ~/.xsession-errors but all of them look "normal". As I said, I've already tried googling most suspicious of the error messages but found nothing even remotely similar to my problem. There were several hits to bug reports and known problems but nothing comparable to crashes I am experiencing.

I will keep digging and post results, if any, here.