Ubuntu Unity および GNOME 3 で自動ログアウトが発生する理由を調べるにはどうすればよいでしょうか?

Ubuntu Unity および GNOME 3 で自動ログアウトが発生する理由を調べるにはどうすればよいでしょうか?

私の Ubuntu 15.04 インストールは、Unity と GNOME 3 の両方で自動的にログアウトしますが、GNOME Fallback ではログアウトしません。この動作の原因を突き止めるには、Xorg 0 ログ ファイルを参照すればよいのでしょうか? また、答えが「はい」の場合、具体的に何を探せばよいのでしょうか?

編集: ご要望に応じて、出力は次のとおりです。

[    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

関連情報