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Francois Marier: Debugging gnome-session problems on Ubuntu 14.04

Thu, 2016-08-25 16:02

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: 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

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.

Maxim Zakharov: Small fix for AMP WordPress plugin

Wed, 2016-08-24 12:03

If you use AMP plugin for WordPress to make AMP (Accelerated Mobile Pages) version of your posts and have some troubles validating them on AMP validator, you may try this fix for AMP plugin to make those pages valid.