I have recently been unable to login to Ubuntu in Unity 3D mode. I can log into Unity 2D mode without problems.
When the problem first started, I checked the log files, and found this in my syslog file around the time I tried to log in:
A little bit of googling suggested I could try fixing the problem by typing
Oct 28 17:09:14 beast kernel: [ 202.447509] show_signal_msg: 39 callbacks suppressed
Oct 28 17:09:14 beast kernel: [ 202.447512] compiz: segfault at 0 ip (null) sp 00007fff049bbe88 error 14 in compiz[400000+c000]
Oct 28 17:09:23 beast gnome-session: WARNING: Application 'compiz.desktop' killed by signal
Oct 28 17:09:23 beast gnome-session: WARNING: App 'compiz.desktop' respawning too quickly
Oct 28 17:09:23 beast gnome-session: CRITICAL: We failed, but the fail whale is dead. Sorry....
I tried this, but I still can't log in. However, the error messages about compiz are now gone from my syslog file. In fact I can't find anything in my syslog file that looks like it's reporting an error at the time I try to log in.
Unity 2D still works just fine.
I'm using Ubuntu 12.04 with NVidia proprietary drivers.
Any ideas what to check next?