log-in screen loops indefinitely

[Richard Stobart]

New installation of Ubunto 14.04 delivered on a Dell Precision Tower 5810. After first major upgrade including updates to kernel and NVIDIA graphics drivers, this issue appeared.

\\loin screen appears - then when password is entered and either mouse-click or CR, the screen goes black and after a short time (1-2s) the log on screen re-appears.

None of the suggested repair routes have worked. (Routes include trying gdm, updating lightdm and gdm.)
NVIDIA graphics card is Quadro K1200.

Description 14.04.5 LTS, release 14.04

Package is xorg.

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: lightdm 1.10.6-0ubuntu1
ProcVersionSignature: Ubuntu 4.4.0-38.57~14.04.1-generic 4.4.19
Uname: Linux 4.4.0-38-generic x86_64
ApportVersion: 2.14.1-0ubuntu3.21
Architecture: amd64
Date: Sun Oct 2 20:25:25 2016
DistributionChannelDescriptor:
 # This is a distribution channel descriptor
 # For more information see http://wiki.ubuntu.com/DistributionChannelDescriptor
 canonical-oem-somerville-trusty-amd64-osp1-20150720-0
InstallationDate: Installed on 2016-09-25 (6 days ago)
InstallationMedia: Ubuntu 14.04 "Trusty" - Build amd64 LIVE Binary 20150720-04:06
LightdmConfig:
 [SeatDefaults]
 autologin-guest=false
 autologin-user-timeout=0
 autologin-session=lightdm-autologin
SourcePackage: lightdm
UpgradeStatus: No upgrade log present (probably fresh install)

[Robert Ancell (robert-ancell)]

The relevant parts of lightdm.log show:

[+16.34s] DEBUG: Session pid=5887: Running command /usr/sbin/lightdm-session gnome-session --session=ubuntu
[+16.34s] DEBUG: Creating shared data directory /var/lib/lightdm-data/richard
[+16.34s] DEBUG: Session pid=5887: Logging to .xsession-errors
[+16.37s] DEBUG: Activating VT 7
[+16.37s] DEBUG: Activating login1 session c28
[+16.98s] DEBUG: Session pid=5887: Exited with return value 0

Which is showing that the session has immediately ended as soon as you logged in. You might be able to better debug this by checking ~/richard/.xsession-errors after this occurs.

[Richard Stobart (richard-stobart)]

.xsession-errors contains:

Xlib: extension "GLX" missing on display ":0".
Xlib: extension "GLX" missing on display ":0".
Script for ibus started at run_im.
Script for auto started at run_im.
Script for default started at run_im.
init: gnome-session (Unity) main process (2719) terminated with status 1
init: Disconnected from notified D-Bus bus
init: logrotate main process (2579) killed by TERM signal
init: update-notifier-crash (/var/crash/susres.2016-10-03_08:56:40.650760.crash) main process (2613) killed by TERM signal
init: update-notifier-crash (/var/crash/_usr_bin_eog.1001.crash) main process (2615) killed by TERM signal
init: update-notifier-crash (/var/crash/_usr_lib_gvfs_gvfsd-afp.1001.crash) main process (2616) killed by TERM signal
init: update-notifier-crash (/var/crash/_usr_lib_gvfs_gvfsd-afp-browse.1001.crash) main process (2625) killed by TERM signal
init: update-notifier-crash (/var/crash/_usr_lib_ibus_ibus-ui-gtk3.1001.crash) main process (2626) killed by TERM signal
init: update-notifier-crash (/var/crash/_usr_lib_virtualbox_VirtualBox.0.crash) main process (2627) killed by TERM signal
init: update-notifier-crash (/var/crash/_usr_share_software-center_software-center.1001.crash) main process (2628) killed by TERM signal
init: update-notifier-crash (/var/crash/_usr_bin_compiz.1001.crash) main process (2614) killed by TERM signal
init: xsession-init main process (2705) killed by TERM signal
init: hud main process (2712) killed by TERM signal
init: unity-panel-service main process (2732) killed by TERM signal
init: window-stack-bridge main process (2609) killed by KILL signal

Critical line is
"gnome-session (Unity) main process (2719) terminated with status 1"

Similar posts on Ubuntu blogs point to a graphics driver incompatibility - in my case caused by the recent substantial upgrade.