我有一台联想 Thinkpad t440s，配有英特尔显卡，运行 Ubuntu Desktop Trusty 14.04.4 LTS。这个问题发生在连接了两个外接显示器的 ThinkPad Ultra Dock 上。
启动后，我可以看到登录屏幕一秒钟，然后两个外部屏幕都变黑（无信号）。如果使用Ctrl+ Alt +切换到控制台登录F1，外部显示器就会启动。现在，只有笔记本电脑盖关闭时才会发生这种情况，所以我必须一直打开它，在这种情况下，两个外部显示器就可以正常工作。
另外，我注意到使用外接显示器登录时会有相当长的延迟（大约 15 秒），如果笔记本电脑没有连接到扩展坞则不会出现这种延迟。
任何指点都将不胜感激。
以下是 x-0-greeter.log
[+0.00s] DEBUG: unity-greeter.vala:496: Starting unity-greeter 14.04.11 UID=112 LANG=en_US.UTF-8
[+0.00s] DEBUG: unity-greeter.vala:499: Setting cursor
[+0.00s] DEBUG: unity-greeter.vala:513: Loading command line options
[+0.00s] DEBUG: unity-greeter.vala:541: Setting GTK+ settings
[+0.05s] DEBUG: unity-greeter.vala:564: Creating Unity Greeter
[+0.05s] DEBUG: unity-greeter.vala:57: Creating background surface
[+0.05s] DEBUG: Connecting to display manager...
[+0.05s] DEBUG: Wrote 18 bytes to daemon
[+0.05s] DEBUG: Read 8 bytes from daemon
[+0.05s] DEBUG: Read 150 bytes from daemon
[+0.05s] DEBUG: Connected version=1.10.6 default-session=ubuntu show-manual-login=false hide-users=false has-guest-account=true show-remote-login=true
[+0.07s] DEBUG: menubar.vala:336: LANG=en_US.UTF-8 LANGUAGE=(null)
[+0.07s] DEBUG: menubar.vala:368: LANG=en_US.UTF-8 LANGUAGE=(null)
[+0.08s] DEBUG: Loading users from org.freedesktop.Accounts
[+0.08s] DEBUG: User /org/freedesktop/Accounts/User1000 added
[+0.08s] DEBUG: user-list.vala:1030: Adding/updating user angel (Angel Kafazov)
[+0.08s] DEBUG: Loading sessions from org.freedesktop.DisplayManager
[+0.08s] DEBUG: user-list.vala:1012: Adding guest account entry
[+0.09s] DEBUG: Loaded session /usr/share/xsessions/ubuntu.desktop (Ubuntu, This session logs you into Ubuntu)
[+0.09s] DEBUG: Starting authentication for user angel...
[+0.09s] DEBUG: Wrote 21 bytes to daemon
[+0.09s] DEBUG: main-window.vala:185: Screen is 1920x1080 pixels
[+0.09s] DEBUG: main-window.vala:193: Monitor 0 is 1920x1080 pixels at 0,0
[+0.09s] DEBUG: main-window.vala:193: Monitor 1 is 1920x1080 pixels at 0,0
[+0.09s] DEBUG: main-window.vala:193: Monitor 2 is 1920x1080 pixels at 0,0
[+0.09s] DEBUG: unity-greeter.vala:567: Showing greeter
[+0.09s] DEBUG: unity-greeter.vala:252: Showing main window
[+0.10s] DEBUG: background.vala:483: Regenerating backgrounds
[+0.10s] DEBUG: background.vala:68: Making background /usr/share/backgrounds/warty-final-ubuntu.png at 1920x1080
[+0.10s] DEBUG: unity-greeter.vala:610: Starting main loop
[+0.10s] DEBUG: Read 8 bytes from daemon
[+0.10s] DEBUG: Read 35 bytes from daemon
[+0.10s] DEBUG: Prompt user with 1 message(s)
[+0.11s] DEBUG: background.vala:68: Making background /usr/share/backgrounds/Reflections_by_Trenton_Fox.jpg at 1920x1080
[+0.14s] DEBUG: settings-daemon.vala:75: Acquired org.gnome.SessionManager
[+0.14s] DEBUG: settings-daemon.vala:102: Acquired org.gnome.ScreenSaver
[+0.14s] DEBUG: settings-daemon.vala:159: All bus names acquired, starting unity-settings-daemon
[+0.19s] DEBUG: unity-greeter.vala:235: starting system-ready sound
[+0.22s] DEBUG: menubar.vala:538: Adding indicator object 0x13689d0 at position 0
[+0.23s] DEBUG: Connected to Application Indicator Service.
[+0.26s] DEBUG: menubar.vala:538: Adding indicator object 0x1368710 at position 0
[+0.28s] DEBUG: Request current apps
[+0.31s] DEBUG: menubar.vala:538: Adding indicator object 0x1368f50 at position 2
[+0.38s] DEBUG: main-window.vala:185: Screen is 1920x1080 pixels
[+0.38s] DEBUG: main-window.vala:193: Monitor 0 is 1920x1080 pixels at 0,0
[+0.38s] DEBUG: main-window.vala:193: Monitor 1 is 1920x1080 pixels at 0,0
[+0.38s] DEBUG: main-window.vala:193: Monitor 2 is 1920x1080 pixels at 0,0
[+0.39s] DEBUG: background.vala:121: Render of background /usr/share/backgrounds/Reflections_by_Trenton_Fox.jpg complete
[+0.42s] DEBUG: menubar.vala:538: Adding indicator object 0x1368450 at position 3
[+0.42s] DEBUG: background.vala:121: Render of background /usr/share/backgrounds/warty-final-ubuntu.png complete
[+0.49s] DEBUG: main-window.vala:185: Screen is 5760x1080 pixels
[+0.49s] DEBUG: main-window.vala:193: Monitor 0 is 1920x1080 pixels at 0,0
[+0.49s] DEBUG: main-window.vala:193: Monitor 1 is 1920x1080 pixels at 1920,0
[+0.49s] DEBUG: main-window.vala:193: Monitor 2 is 1920x1080 pixels at 3840,0
[+0.63s] DEBUG: background.vala:483: Regenerating backgrounds
[+0.63s] DEBUG: background.vala:68: Making background /usr/share/backgrounds/warty-final-ubuntu.png at 1920x1080
[+0.63s] DEBUG: background.vala:68: Making background /usr/share/backgrounds/Reflections_by_Trenton_Fox.jpg at 1920x1080
[+0.73s] DEBUG: menubar.vala:538: Adding indicator object 0x1368c90 at position 3
** (nm-applet:3495): CRITICAL **: nm_secret_agent_register: assertion 'priv->registered == FALSE' failed
[+0.81s] DEBUG: Building new application entry: :1.20 with icon: nm-device-wired at position 0
[+0.81s] DEBUG: menubar.vala:538: Adding indicator object 0x17ce4e0 at position 5
** (unity-settings-daemon:3517): WARNING **: Unable to register client: GDBus.Error:org.freedesktop.DBus.Error.UnknownMethod: No such method 'RegisterClient'
[+1.02s] DEBUG: background.vala:121: Render of background /usr/share/backgrounds/Reflections_by_Trenton_Fox.jpg complete
[+1.03s] DEBUG: background.vala:121: Render of background /usr/share/backgrounds/warty-final-ubuntu.png complete
[+5.16s] DEBUG: Providing response to display manager
[+5.16s] DEBUG: Wrote 25 bytes to daemon
[+5.17s] DEBUG: Read 8 bytes from daemon
[+5.17s] DEBUG: Read 17 bytes from daemon
[+5.17s] DEBUG: Authentication complete for user angel with return code 0
[+5.17s] DEBUG: Starting session ubuntu
[+5.17s] DEBUG: Wrote 18 bytes to daemon
[+5.17s] DEBUG: Read 8 bytes from daemon
[+5.17s] DEBUG: Read 4 bytes from daemon
[+5.17s] DEBUG: unity-greeter.vala:605: Got a SIGTERM
[+5.17s] DEBUG: unity-greeter.vala:613: Cleaning up
[+5.17s] DEBUG: unity-greeter.vala:621: Upstart exited with return value 0
[+5.17s] DEBUG: unity-greeter.vala:633: AT-SPI exited with return value 0
[+5.17s] DEBUG: unity-greeter.vala:639: Exiting
init: indicator-power main process (3510) killed by TERM signal
init: indicator-bluetooth main process (3504) killed by TERM signal
init: indicator-messages main process (3498) killed by TERM signal
init: indicator-datetime main process (3512) killed by TERM signal
init: indicator-session main process (3519) killed by TERM signal
g_dbus_connection_real_closed: Remote peer vanished with error: Underlying GIOStream returned 0 bytes on an async read (g-io-error-quark, 0). Exiting.
nm-applet-Message: PID 3495 (we are 3495) sent signal 15, shutting down...
init: indicator-application main process (3537) killed by TERM signal
** (unity-settings-daemon:3517): WARNING **: Name taken or bus went away - shutting down
(nm-applet:3495): libappindicator-WARNING **: Unable to send signal for NewStatus: The connection is closed
(unity-settings-daemon:3517): dconf-WARNING **: failed to commit changes to dconf: The connection is closed
g_dbus_connection_real_closed: Remote peer vanished with error: Underlying GIOStream returned 0 bytes on an async read (g-io-error-quark, 0). Exiting.
(nm-applet:3495): GLib-CRITICAL **: Source ID 132 was not found when attempting to remove it