After upgrading an Ubuntu 14.04 ("trusty") machine to the latest 16.04 Hardware Enablement packages, I ran into login problems. I could log into my user account and see the GNOME desktop for a split second before getting thrown back into the LightDM login manager.
The solution I found was to install this missing package:
apt install libwayland-egl1-mesa-lts-xenial
Looking for clues in the logs
The first place I looked was the log file for the login manager
(/var/log/lightdm/lightdm.log) where I found the following:
DEBUG: Session pid=12743: Running command /usr/sbin/lightdm-session gnome-session --session=gnome
DEBUG: Creating shared data directory /var/lib/lightdm-data/username
DEBUG: Session pid=12743: Logging to .xsession-errors
This told me that the login manager runs the gnome-session command and
gets it to create a session of type gnome. That command line is defined
in /usr/share/xsessions/gnome.desktop (look for Exec=):
[Desktop Entry]
Name=GNOME
Comment=This session logs you into GNOME
Exec=gnome-session --session=gnome
TryExec=gnome-shell
X-LightDM-DesktopName=GNOME
I couldn't see anything unexpected there, but it did point to another log
file (~/.xsession-errors) which contained the following:
Script for ibus started at run_im.
Script for auto started at run_im.
Script for default started at run_im.
init: Le processus gnome-session (GNOME) main (11946) s'est achevé avec l'état 1
init: Déconnecté du bus D-Bus notifié
init: Le processus logrotate main (11831) a été tué par le signal TERM
init: Le processus update-notifier-crash (/var/crash/_usr_bin_unattended-upgrade.0.crash) main (11908) a été tué par le signal TERM
Seaching for French error messages isn't as useful as searching for English
ones, so I took a look at /var/log/syslog and found this:
gnome-session[4134]: WARNING: App 'gnome-shell.desktop' exited with code 127
gnome-session[4134]: WARNING: App 'gnome-shell.desktop' exited with code 127
gnome-session[4134]: WARNING: App 'gnome-shell.desktop' respawning too quickly
gnome-session[4134]: CRITICAL: We failed, but the fail whale is dead. Sorry....
It looks like gnome-session is executing gnome-shell and that this last
command is terminating prematurely. This would explain why gnome-session
exits immediately after login.
Increasing the amount of logging
In order to get more verbose debugging information out of gnome-session, I
created a new type of session (GNOME debug) by copying the regular GNOME
session:
cp /usr/share/xsessions/gnome.desktop /usr/share/xsessions/gnome-debug.desktop
and then adding --debug to the command line inside gnome-debug.desktop:
[Desktop Entry]
Name=GNOME debug
Comment=This session logs you into GNOME debug
Exec=gnome-session --debug --session=gnome
TryExec=gnome-shell
X-LightDM-DesktopName=GNOME debug
After restarting LightDM (service lightdm restart), I clicked the GNOME
logo next to the password field and chose GNOME debug before trying to
login again.
This time, I had a lot more information in ~/.xsession-errors:
gnome-session[12878]: DEBUG(+): GsmAutostartApp: starting gnome-shell.desktop: command=/usr/bin/gnome-shell startup-id=10d41f1f5c81914ec61471971137183000000128780000
gnome-session[12878]: DEBUG(+): GsmAutostartApp: started pid:13121
...
/usr/bin/gnome-shell: error while loading shared libraries: libwayland-egl.so.1: cannot open shared object file: No such file or directory
gnome-session[12878]: DEBUG(+): GsmAutostartApp: (pid:13121) done (status:127)
gnome-session[12878]: WARNING: App 'gnome-shell.desktop' exited with code 127
which suggests that gnome-shell won't start because of a missing library.
Finding the missing library
To find the missing library, I used the apt-file command:
apt-file update
apt-file search libwayland-egl.so.1
and found that this file is provided by the following packages:
- libhybris
- libwayland-egl1-mesa
- libwayland-egl1-mesa-dbg
- libwayland-egl1-mesa-lts-utopic
- libwayland-egl1-mesa-lts-vivid
- libwayland-egl1-mesa-lts-wily
- libwayland-egl1-mesa-lts-xenial
Since I installed the LTS Enablement stack, the package I needed to install to fix this was libwayland-egl1-mesa-lts-xenial.
I filed a bug for this on Launchpad.