Как выяснить причину автоматического выхода из системы в Ubuntu Unity и GNOME 3?

Моя установка Ubuntu 15.04 автоматически выходит из системы как в Unity, так и в GNOME 3, но не в GNOME Fallback. Является ли файл журнала Xorg 0 тем местом, куда мне следует обратиться, чтобы выяснить причину такого поведения? И, если ответ «да», что именно я должен искать?

Редактировать: По запросу, вот вывод:

[    58.984] (**) Option "xkb_layout" "us,ara"
[    58.984] (**) Option "xkb_variant" ","
[    58.984] (**) Option "xkb_options" "grp:alt_shift_toggle,grp_led:scroll"
[    71.806] (II) modeset(0): EDID vendor "CMO", prod id 5540
[    71.806] (II) modeset(0): Printing DDC gathered Modelines:
[    71.807] (II) modeset(0): Modeline "1366x768"x0.0   76.80  1366 1392 1448 1580  768 772 785 810 +hsync -vsync (48.6 kHz eP)
[    72.150] (II) XKB: reuse xkmfile /var/lib/xkb/server-B20D7FC79C7F597315E3E501AEF10E0D866E8E92.xkm
[    74.447] (II) modeset(0): EDID vendor "CMO", prod id 5540
[    74.447] (II) modeset(0): Printing DDC gathered Modelines:
[    74.447] (II) modeset(0): Modeline "1366x768"x0.0   76.80  1366 1392 1448 1580  768 772 785 810 +hsync -vsync (48.6 kHz eP)
[    74.683] (II) XKB: reuse xkmfile /var/lib/xkb/server-1EBBE7F05AE979C030B4F61D845BA40EFA576552.xkm
[    74.730] (II) XKB: reuse xkmfile /var/lib/xkb/server-1EBBE7F05AE979C030B4F61D845BA40EFA576552.xkm
[    74.857] (II) XKB: reuse xkmfile /var/lib/xkb/server-A1C2FAC6D30A4D0BE5D026BF99AE277EFAEE8014.xkm
[    74.951] (II) XKB: reuse xkmfile /var/lib/xkb/server-A1C2FAC6D30A4D0BE5D026BF99AE277EFAEE8014.xkm
[    74.958] (II) XKB: reuse xkmfile /var/lib/xkb/server-A1C2FAC6D30A4D0BE5D026BF99AE277EFAEE8014.xkm
[    74.965] (II) XKB: reuse xkmfile /var/lib/xkb/server-A1C2FAC6D30A4D0BE5D026BF99AE277EFAEE8014.xkm
[    74.972] (II) XKB: reuse xkmfile /var/lib/xkb/server-A1C2FAC6D30A4D0BE5D026BF99AE277EFAEE8014.xkm
[    74.980] (II) XKB: reuse xkmfile /var/lib/xkb/server-A1C2FAC6D30A4D0BE5D026BF99AE277EFAEE8014.xkm
[    74.987] (II) XKB: reuse xkmfile /var/lib/xkb/server-A1C2FAC6D30A4D0BE5D026BF99AE277EFAEE8014.xkm
[    74.994] (II) XKB: reuse xkmfile /var/lib/xkb/server-A1C2FAC6D30A4D0BE5D026BF99AE277EFAEE8014.xkm
[    75.001] (II) XKB: reuse xkmfile /var/lib/xkb/server-A1C2FAC6D30A4D0BE5D026BF99AE277EFAEE8014.xkm
[    75.009] (II) XKB: reuse xkmfile /var/lib/xkb/server-A1C2FAC6D30A4D0BE5D026BF99AE277EFAEE8014.xkm
[    75.016] (II) XKB: reuse xkmfile /var/lib/xkb/server-A1C2FAC6D30A4D0BE5D026BF99AE277EFAEE8014.xkm
[    75.023] (II) XKB: reuse xkmfile /var/lib/xkb/server-A1C2FAC6D30A4D0BE5D026BF99AE277EFAEE8014.xkm
[    75.031] (II) XKB: reuse xkmfile /var/lib/xkb/server-A1C2FAC6D30A4D0BE5D026BF99AE277EFAEE8014.xkm
[    75.039] (II) XKB: reuse xkmfile /var/lib/xkb/server-A1C2FAC6D30A4D0BE5D026BF99AE277EFAEE8014.xkm
[    75.046] (II) XKB: reuse xkmfile /var/lib/xkb/server-A1C2FAC6D30A4D0BE5D026BF99AE277EFAEE8014.xkm
[    75.054] (II) XKB: reuse xkmfile /var/lib/xkb/server-A1C2FAC6D30A4D0BE5D026BF99AE277EFAEE8014.xkm
[    75.061] (II) XKB: reuse xkmfile /var/lib/xkb/server-A1C2FAC6D30A4D0BE5D026BF99AE277EFAEE8014.xkm
[    75.069] (II) XKB: reuse xkmfile /var/lib/xkb/server-A1C2FAC6D30A4D0BE5D026BF99AE277EFAEE8014.xkm
[    75.076] (II) XKB: reuse xkmfile /var/lib/xkb/server-A1C2FAC6D30A4D0BE5D026BF99AE277EFAEE8014.xkm
[    75.084] (II) XKB: reuse xkmfile /var/lib/xkb/server-A1C2FAC6D30A4D0BE5D026BF99AE277EFAEE8014.xkm
[    75.091] (II) XKB: reuse xkmfile /var/lib/xkb/server-A1C2FAC6D30A4D0BE5D026BF99AE277EFAEE8014.xkm
[    95.792] (II) modeset(0): EDID vendor "CMO", prod id 5540
[    95.792] (II) modeset(0): Printing DDC gathered Modelines:
[    95.792] (II) modeset(0): Modeline "1366x768"x0.0   76.80  1366 1392 1448 1580  768 772 785 810 +hsync -vsync (48.6 kHz eP)
[    95.794] (II) modeset(0): EDID vendor "CMO", prod id 5540
[    95.794] (II) modeset(0): Printing DDC gathered Modelines:
[    95.794] (II) modeset(0): Modeline "1366x768"x0.0   76.80  1366 1392 1448 1580  768 772 785 810 +hsync -vsync (48.6 kHz eP)
[   343.578] (II) XKB: reuse xkmfile /var/lib/xkb/server-0E9687517A6661DDB904DA5E2AD2FDCBF7B8EBA7.xkm
[   343.604] (II) XKB: generating xkmfile /var/lib/xkb/server-9BEB1120B3B8F5164896EFCC810874661DE6EF1D.xkm
[   343.638] (II) XKB: reuse xkmfile /var/lib/xkb/server-9BEB1120B3B8F5164896EFCC810874661DE6EF1D.xkm
[   343.648] (II) XKB: reuse xkmfile /var/lib/xkb/server-9BEB1120B3B8F5164896EFCC810874661DE6EF1D.xkm
[   343.659] (II) XKB: reuse xkmfile /var/lib/xkb/server-9BEB1120B3B8F5164896EFCC810874661DE6EF1D.xkm
[   343.671] (II) XKB: reuse xkmfile /var/lib/xkb/server-9BEB1120B3B8F5164896EFCC810874661DE6EF1D.xkm
[   343.682] (II) XKB: reuse xkmfile /var/lib/xkb/server-9BEB1120B3B8F5164896EFCC810874661DE6EF1D.xkm
[   343.692] (II) XKB: reuse xkmfile /var/lib/xkb/server-9BEB1120B3B8F5164896EFCC810874661DE6EF1D.xkm
[   343.702] (II) XKB: reuse xkmfile /var/lib/xkb/server-9BEB1120B3B8F5164896EFCC810874661DE6EF1D.xkm
[   343.712] (II) XKB: reuse xkmfile /var/lib/xkb/server-9BEB1120B3B8F5164896EFCC810874661DE6EF1D.xkm
[   343.722] (II) XKB: reuse xkmfile /var/lib/xkb/server-9BEB1120B3B8F5164896EFCC810874661DE6EF1D.xkm