我安装的 Ubuntu 15.04 在 Unity 和 GNOME 3 上都会自动注销，但在 GNOME Fallback 上不会。我应该去 Xorg 0 日志文件来找出这种行为的原因吗？如果答案是肯定的，我到底应该寻找什么？
编辑：根据要求，这里是输出：
[ 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