Users authenticate against LDAP. Was fine until I upgraded to Ubuntu 18.04. /home is nfs mounted.
I've checked all logs I can find, syslog, auth, kern, lightdm, Xorg, .xsession-errors. My main suspect from auth.log is:
lightdm: pam_systemd(lightdm:session): Failed to create session: Connection timed out
There seems to be a 25 second timeout and if the session isn't ready it goes back to the login screen (here lightdm-greeter).
Something else is bugging me: when a given session DOES let me login, after restarting lightdm for whatever reason, I won't be able to log back in. It's like the lightdm restart doesn't properly terminate, and some bad clues are left in the user's home folder so that the next try will end in a login loop.
Reinstalling flashback with apt-get install --reinstall gnome-session-flashback didn't help.
~/.Xauthority is owned and writable by the owner. This has never been a problem.
No login problem for an old local account.
---
ProblemType: Bug
ApportVersion: 2.20.9-0ubuntu7.5
Architecture: amd64
CurrentDesktop: GNOME-Flashback:GNOME
DistroRelease: Ubuntu 18.04
InstallationDate: Installed on 2016-12-18 (693 days ago)
InstallationMedia: Ubuntu 16.04 LTS "Xenial Xerus" - Release amd64 (20160420.1)
Package: gnome-flashback 3.28.0-1ubuntu1.3
PackageArchitecture: amd64
ProcVersionSignature: Ubuntu 4.15.0-39.42-generic 4.15.18
Tags: bionic package-from-proposed
Uname: Linux 4.15.0-39-generic x86_64
UpgradeStatus: Upgraded to bionic on 2018-11-03 (7 days ago)
UserGroups: adm adm cdrom cdrom dip dip lpadmin lpadmin plugdev plugdev sambashare sambashare sudo sudo
_MarkForUpload: True
Well this starts sound like problem is somewhere else... Do I understand correctly that you can not login only in LDAP?