我遇到一个问题，在测试模式下运行时 LightDM 无法启动lightdm --test-mode。
当我在调试中运行同样的事情时，输出如下：
[+0.00s] DEBUG: Logging to /home/vilsol/.cache/lightdm/log/lightdm.log
[+0.00s] DEBUG: Starting Light Display Manager 1.14.2, UID=1000 PID=31996
[+0.00s] DEBUG: Loading configuration dirs from /usr/share/lightdm/lightdm.conf.d
[+0.00s] DEBUG: Loading configuration from /usr/share/lightdm/lightdm.conf.d/40-lightdm-webkit-greeter.conf
[+0.00s] DEBUG: Loading configuration from /usr/share/lightdm/lightdm.conf.d/50-greeter-wrapper.conf
[+0.00s] DEBUG: Loading configuration from /usr/share/lightdm/lightdm.conf.d/50-guest-wrapper.conf
[+0.00s] DEBUG: Loading configuration from /usr/share/lightdm/lightdm.conf.d/50-ubuntu.conf
[+0.00s] DEBUG: Loading configuration from /usr/share/lightdm/lightdm.conf.d/50-unity-greeter.conf
[+0.00s] DEBUG: Loading configuration from /usr/share/lightdm/lightdm.conf.d/50-xserver-command.conf
[+0.00s] DEBUG: Loading configuration dirs from /usr/local/share/lightdm/lightdm.conf.d
[+0.00s] DEBUG: Loading configuration dirs from /usr/share/gnome/lightdm/lightdm.conf.d
[+0.00s] DEBUG: Loading configuration dirs from /etc/xdg/lightdm/lightdm.conf.d
[+0.00s] DEBUG: Loading configuration dirs from /usr/share/upstart/xdg/lightdm/lightdm.conf.d
[+0.00s] DEBUG: Loading configuration dirs from /etc/xdg/xdg-gnome/lightdm/lightdm.conf.d
[+0.00s] DEBUG: Loading configuration from /etc/lightdm/lightdm.conf
[+0.00s] DEBUG: Using D-Bus name org.freedesktop.DisplayManager
[+0.00s] DEBUG: Running in user mode
[+0.00s] DEBUG: Using Xephyr for X servers
[+0.00s] DEBUG: Registered seat module xlocal
[+0.00s] DEBUG: Registered seat module xremote
[+0.00s] DEBUG: Registered seat module unity
[+0.01s] DEBUG: Monitoring logind for seats
[+0.01s] DEBUG: New seat added from logind: seat0
[+0.01s] DEBUG: Loading properties from config section SeatDefaults
[+0.01s] DEBUG: Seat seat0: Starting
[+0.01s] DEBUG: Seat seat0: Creating greeter session
[+0.01s] DEBUG: Loading users from org.freedesktop.Accounts
[+0.01s] DEBUG: User /org/freedesktop/Accounts/User1000 added
[+0.02s] DEBUG: User /org/freedesktop/Accounts/User1002 added
[+0.02s] DEBUG: User /org/freedesktop/Accounts/User1001 added
[+0.02s] DEBUG: Seat seat0: Creating display server of type x
[+0.02s] DEBUG: Seat seat0: Starting local X display
[+0.02s] DEBUG: DisplayServer x-1: Logging to /home/vilsol/.cache/lightdm/log/x-1.log
[+0.02s] DEBUG: DisplayServer x-1: Writing X server authority to /home/vilsol/.cache/lightdm/run/root/:1
[+0.03s] DEBUG: DisplayServer x-1: Launching X Server
[+0.03s] DEBUG: Launching process 32000: /usr/bin/Xephyr :1 -seat seat0 -auth /home/vilsol/.cache/lightdm/run/root/:1 -nolisten tcp
[+0.03s] DEBUG: DisplayServer x-1: Waiting for ready signal from X server :1
[+0.03s] DEBUG: Acquired bus name org.freedesktop.DisplayManager
[+0.03s] DEBUG: Registering seat with bus path /org/freedesktop/DisplayManager/Seat0
[+0.07s] DEBUG: Got signal 10 from process 32000
[+0.07s] DEBUG: DisplayServer x-1: Got signal from X server :1
[+0.07s] DEBUG: DisplayServer x-1: Connecting to XServer :1
[+0.08s] DEBUG: Seat seat0: Display server ready, starting session authentication
[+0.08s] DEBUG: Session: Not setting XDG_VTNR
[+0.08s] DEBUG: Session pid=32012: Started with service 'lightdm-greeter', username 'vilsol'
[+0.08s] DEBUG: Session pid=32012: Authentication complete with return value 0: Success
[+0.08s] DEBUG: Seat seat0: Session authenticated, running command
[+0.08s] DEBUG: Session pid=32012: Not setting XDG_VTNR
[+0.08s] DEBUG: Session pid=32012: Running command /usr/lib/lightdm/lightdm-greeter-session /usr/bin/lightdm-webkit-greeter
[+0.08s] DEBUG: Creating shared data directory /var/lib/lightdm-data/vilsol
[+0.08s] DEBUG: Session pid=32012: Logging to /home/vilsol/.cache/lightdm/log/x-1-greeter.log
[+0.20s] DEBUG: Session pid=32012: Greeter closed communication channel
[+0.20s] DEBUG: Session pid=32012: Terminated with signal 11
[+0.20s] DEBUG: Seat seat0: Session stopped
[+0.20s] DEBUG: Seat seat0: Stopping; failed to start a greeter
[+0.20s] DEBUG: Seat seat0: Stopping
[+0.20s] DEBUG: Seat seat0: Stopping display server
[+0.20s] DEBUG: Sending signal 15 to process 32000
[+0.21s] DEBUG: Process 32000 exited with return value 0
[+0.21s] DEBUG: DisplayServer x-1: X server stopped
[+0.21s] DEBUG: DisplayServer x-1: Removing X server authority /home/vilsol/.cache/lightdm/run/root/:1
[+0.21s] DEBUG: Seat seat0: Display server stopped
[+0.21s] DEBUG: Seat seat0: Stopped
[+0.21s] DEBUG: Required seat has stopped
[+0.21s] DEBUG: Stopping display manager
[+0.21s] DEBUG: Display manager stopped
[+0.21s] DEBUG: Stopping daemon
[+0.21s] DEBUG: Exiting with return value 1
没有实际错误，但出于某种原因，欢迎程序说欢迎程序未启动。如果我重新启动，LightDM 就会正常显示，所以这一定与测试模式有关。
答案1
仅用于档案，因为这个问题已经很老了（但却是谷歌的最佳搜索结果）。
如果您查看 $HOME/.cache/lightdm/log/x-0.log，您可能会看到其他类似错误：
Fatal server error:
(EE) Cannot establish any listening sockets - Make sure an X server isn't already running(EE)
_XSERVTransSocketUNIXCreateListener: ...SocketCreateListener() failed
_XSERVTransMakeAllCOTSServerListeners: server already running
(EE)
当您使用“--test-mode”进行测试时，您应该使用 lightdm 作为显示管理器（这有点不直观，运行某些东西，首先要测试...）。也许您正在运行 gdm3 或另一个 dm？