Every time I try to log via a DM it fails. I have attached part of lightdm.log, but I have also tried kdm and gdm with about same result.
Authentification is successful, the session seems to start normally, but for some reason exits after 0.05 sec. Effective user experience is black screen and the greeter again. No errors in Xorg.0.log or syslog.
If I log in to console and run startx it works just perfectly.
$ lsb_release -rd
Description: Ubuntu 12.10
Release: 12.10
ProblemType: Bug
DistroRelease: Ubuntu 12.10
Package: xorg 1:7.7+1ubuntu4
ProcVersionSignature: Ubuntu 3.5.0-18.29-generic 3.5.7
Uname: Linux 3.5.0-18-generic x86_64
ApportVersion: 2.6.1-0ubuntu6
Architecture: amd64
Date: Wed Nov 7 16:07:57 2012
InstallationDate: Installed on 2012-01-02 (310 days ago)
InstallationMedia: Kubuntu 11.10 "Oneiric Ocelot" - Release amd64 (20111012)
MarkForUpload: True
SourcePackage: xorg
Symptom: display
UpgradeStatus: Upgraded to quantal on 2012-11-06 (0 days ago)
Still no idea what happened to lightdm and gdm, but I have partially fixed the issue: now I can log in via kdm.
Unlike others it crashed X. Logs said something about unrecognised options:
"Fatal server error:
Unrecognized option: -nr"
So I went to /etc/kde4/kdmrc and edited ServerArgsLocal to -background none -nolisten tcp. That fixed the kdm issue.
lightdm and gdm however did not crash X and the problem still remains. They both seem to launch X correctly, however the session terminates immediately. I am still unable to find anything in logs.