我有一台运行 Debian GNU/Linux 的 Intel NUC6i3SYH，带有 LightDM 1.26.0-3、LightDM GTK+ Greeter 2.0.6-1 和 Light Locker 1.8.0-3。当我锁定会话时，断开 DisplayPort 电缆与显示器的连接并尝试登录，LightDM 崩溃（但不是真的，因为systemctl status lightdm仍然显示“活动”旁边的时间相同）并且我的会话丢失。以下是尝试解锁后的输出journalctl（在 19:15 我按空格键激活我的问候语，在 19:16 我输入登录名并按 Enter 键）：
Feb 05 19:15:01 wb9688-nuc6i3syh CRON[4571]: pam_env(cron:session): Unable to open env file: /etc/environment: No such file or directory
Feb 05 19:15:01 wb9688-nuc6i3syh CRON[4571]: pam_unix(cron:session): session opened for user root by (uid=0)
Feb 05 19:15:01 wb9688-nuc6i3syh CRON[4572]: (root) CMD (command -v debian-sa1 > /dev/null && debian-sa1 1 1)
Feb 05 19:15:01 wb9688-nuc6i3syh CRON[4571]: pam_unix(cron:session): session closed for user root
Feb 05 19:15:09 wb9688-nuc6i3syh kernel: [drm:intel_dp_start_link_train [i915]] *ERROR* failed to enable link training
Feb 05 19:15:11 wb9688-nuc6i3syh kernel: [drm:intel_dp_start_link_train [i915]] *ERROR* failed to enable link training
Feb 05 19:15:13 wb9688-nuc6i3syh kernel: [drm:intel_dp_start_link_train [i915]] *ERROR* failed to enable link training
Feb 05 19:16:06 wb9688-nuc6i3syh systemd[1]: session-c4.scope: Killing process 4505 (lightdm) with signal SIGTERM.
Feb 05 19:16:06 wb9688-nuc6i3syh systemd[1]: session-c4.scope: Killing process 4520 (lightdm-gtk-gre) with signal SIGTERM.
Feb 05 19:16:06 wb9688-nuc6i3syh systemd[1]: Stopping Session c4 of user lightdm.
Feb 05 19:16:06 wb9688-nuc6i3syh lightdm[4505]: pam_unix(lightdm-greeter:session): session closed for user lightdm
Feb 05 19:16:06 wb9688-nuc6i3syh systemd[1]: session-c4.scope: Succeeded.
Feb 05 19:16:06 wb9688-nuc6i3syh systemd[1]: Stopped Session c4 of user lightdm.
Feb 05 19:16:07 wb9688-nuc6i3syh systemd-logind[594]: Removed session c4.
Feb 05 19:16:07 wb9688-nuc6i3syh pulseaudio[3889]: XIO: fatal IO error 11 (Resource temporarily unavailable) on X server ":0"
Feb 05 19:16:07 wb9688-nuc6i3syh pulseaudio[3889]: after 17 requests (17 known processed) with 0 events remaining.
Feb 05 19:16:07 wb9688-nuc6i3syh xfce4-notifyd[4491]: xfce4-notifyd: Fatal IO error 11 (Resource temporarily unavailable) on X server :0.
Feb 05 19:16:07 wb9688-nuc6i3syh at-spi-bus-launcher[3864]: XIO: fatal IO error 11 (Resource temporarily unavailable) on X server ":0"
Feb 05 19:16:07 wb9688-nuc6i3syh at-spi-bus-launcher[3864]: after 249 requests (249 known processed) with 0 events remaining.
Feb 05 19:16:07 wb9688-nuc6i3syh bluetoothd[597]: Endpoint unregistered: sender=:1.405 path=/MediaEndpoint/A2DPSource
Feb 05 19:16:07 wb9688-nuc6i3syh systemd[3770]: xfce4-notifyd.service: Main process exited, code=exited, status=1/FAILURE
Feb 05 19:16:07 wb9688-nuc6i3syh bluetoothd[597]: Endpoint unregistered: sender=:1.405 path=/MediaEndpoint/A2DPSink
Feb 05 19:16:07 wb9688-nuc6i3syh systemd[3770]: xfce4-notifyd.service: Failed with result 'exit-code'.
Feb 05 19:16:07 wb9688-nuc6i3syh sudo[4480]: pam_unix(sudo:session): session closed for user root
Feb 05 19:16:07 wb9688-nuc6i3syh systemd[3770]: pulseaudio.service: Main process exited, code=exited, status=1/FAILURE
Feb 05 19:16:07 wb9688-nuc6i3syh systemd[3770]: pulseaudio.service: Failed with result 'exit-code'.
Feb 05 19:16:07 wb9688-nuc6i3syh systemd[1]: session-5.scope: Killing process 3765 (lightdm) with signal SIGTERM.
Feb 05 19:16:07 wb9688-nuc6i3syh systemd[1]: session-5.scope: Killing process 3835 (ssh-agent) with signal SIGTERM.
Feb 05 19:16:07 wb9688-nuc6i3syh systemd[1]: session-5.scope: Killing process 3880 (agent) with signal SIGTERM.
Feb 05 19:16:07 wb9688-nuc6i3syh systemd[1]: session-5.scope: Killing process 3892 (applet.py) with signal SIGTERM.
Feb 05 19:16:07 wb9688-nuc6i3syh systemd[1]: Stopping Session 5 of user wb9688.
Feb 05 19:16:07 wb9688-nuc6i3syh systemd[1]: session-5.scope: Succeeded.
Feb 05 19:16:07 wb9688-nuc6i3syh systemd[1]: Stopped Session 5 of user wb9688.
Feb 05 19:16:07 wb9688-nuc6i3syh systemd-logind[594]: Removed session 5.
Feb 05 19:16:07 wb9688-nuc6i3syh acpid[600]: client 3724[0:0] has disconnected
Feb 05 19:16:07 wb9688-nuc6i3syh acpid[600]: client 4488[0:0] has disconnected
Feb 05 19:16:07 wb9688-nuc6i3syh acpid[600]: client connected from 4585[0:0]
Feb 05 19:16:07 wb9688-nuc6i3syh acpid[600]: 1 client rule loaded
Feb 05 19:16:07 wb9688-nuc6i3syh systemd[3770]: pulseaudio.service: Service RestartSec=100ms expired, scheduling restart.
Feb 05 19:16:07 wb9688-nuc6i3syh systemd[3770]: pulseaudio.service: Scheduled restart job, restart counter is at 1.
Feb 05 19:16:07 wb9688-nuc6i3syh systemd[3770]: Stopped Sound Service.
Feb 05 19:16:07 wb9688-nuc6i3syh systemd[3770]: Starting Sound Service...
Feb 05 19:16:07 wb9688-nuc6i3syh pulseaudio[4592]: W: [pulseaudio] pid.c: Stale PID file, overwriting.
Feb 05 19:16:08 wb9688-nuc6i3syh lightdm[4595]: pam_env(lightdm-greeter:session): Unable to open env file: /etc/environment: No such file or directory
Feb 05 19:16:08 wb9688-nuc6i3syh lightdm[4595]: pam_unix(lightdm-greeter:session): session opened for user lightdm by (uid=0)
Feb 05 19:16:08 wb9688-nuc6i3syh systemd-logind[594]: New session c5 of user lightdm.
Feb 05 19:16:08 wb9688-nuc6i3syh systemd[1]: Started Session c5 of user lightdm.
Feb 05 19:16:09 wb9688-nuc6i3syh rtkit-daemon[609]: Supervising 0 threads of 0 processes of 1 users.
Feb 05 19:16:09 wb9688-nuc6i3syh rtkit-daemon[609]: Supervising 0 threads of 0 processes of 1 users.
Feb 05 19:16:09 wb9688-nuc6i3syh rtkit-daemon[609]: Supervising 0 threads of 0 processes of 1 users.
Feb 05 19:16:09 wb9688-nuc6i3syh rtkit-daemon[609]: Supervising 0 threads of 0 processes of 1 users.
Feb 05 19:16:09 wb9688-nuc6i3syh rtkit-daemon[609]: Supervising 0 threads of 0 processes of 1 users.
Feb 05 19:16:09 wb9688-nuc6i3syh rtkit-daemon[609]: Supervising 0 threads of 0 processes of 1 users.
Feb 05 19:16:09 wb9688-nuc6i3syh rtkit-daemon[609]: Supervising 0 threads of 0 processes of 1 users.
Feb 05 19:16:09 wb9688-nuc6i3syh rtkit-daemon[609]: Supervising 0 threads of 0 processes of 1 users.
Feb 05 19:16:09 wb9688-nuc6i3syh rtkit-daemon[609]: Supervising 0 threads of 0 processes of 1 users.
Feb 05 19:16:09 wb9688-nuc6i3syh rtkit-daemon[609]: Supervising 0 threads of 0 processes of 1 users.
Feb 05 19:16:09 wb9688-nuc6i3syh rtkit-daemon[609]: Supervising 0 threads of 0 processes of 1 users.
Feb 05 19:16:09 wb9688-nuc6i3syh rtkit-daemon[609]: Supervising 0 threads of 0 processes of 1 users.
Feb 05 19:16:09 wb9688-nuc6i3syh rtkit-daemon[609]: Supervising 0 threads of 0 processes of 1 users.
Feb 05 19:16:09 wb9688-nuc6i3syh rtkit-daemon[609]: Supervising 0 threads of 0 processes of 1 users.
Feb 05 19:16:09 wb9688-nuc6i3syh rtkit-daemon[609]: Supervising 0 threads of 0 processes of 1 users.
Feb 05 19:16:09 wb9688-nuc6i3syh rtkit-daemon[609]: Supervising 0 threads of 0 processes of 1 users.
Feb 05 19:16:09 wb9688-nuc6i3syh rtkit-daemon[609]: Supervising 0 threads of 0 processes of 1 users.
Feb 05 19:16:09 wb9688-nuc6i3syh rtkit-daemon[609]: Supervising 0 threads of 0 processes of 1 users.
Feb 05 19:16:09 wb9688-nuc6i3syh rtkit-daemon[609]: Supervising 0 threads of 0 processes of 1 users.
Feb 05 19:16:09 wb9688-nuc6i3syh rtkit-daemon[609]: Supervising 0 threads of 0 processes of 1 users.
Feb 05 19:16:09 wb9688-nuc6i3syh dbus-daemon[610]: [system] Rejected send message, 2 matched rules; type="method_call", sender=":1.650" (uid=1000 pid=4592 comm="/usr/bin/pulseaudio --daemonize=no ") interface="org.freedesktop.DBus.ObjectManager" member="GetManagedObjects" error name="(unset)" requested_reply="0" destination="org.bluez" (uid=0 pid=597 comm="/usr/lib/bluetooth/bluetoothd ")
Feb 05 19:16:09 wb9688-nuc6i3syh systemd[3770]: Started Sound Service.
Feb 05 19:16:09 wb9688-nuc6i3syh pulseaudio[4592]: E: [pulseaudio] bluez5-util.c: GetManagedObjects() failed: org.freedesktop.DBus.Error.AccessDenied: Rejected send message, 2 matched rules; type="method_call", sender=":1.650" (uid=1000 pid=4592 comm="/usr/bin/pulseaudio --daemonize=no ") interface="org.freedesktop.DBus.ObjectManager" member="GetManagedObjects" error name="(unset)" requested_reply="0" destination="org.bluez" (uid=0 pid=597 comm="/usr/lib/bluetooth/bluetoothd ")
Feb 05 19:16:17 wb9688-nuc6i3syh systemd[1]: Stopping User Manager for UID 1000...
Feb 05 19:16:17 wb9688-nuc6i3syh systemd[3770]: Stopped target Default.
Feb 05 19:16:17 wb9688-nuc6i3syh systemd[3770]: Stopping Accessibility services bus...
Feb 05 19:16:17 wb9688-nuc6i3syh systemd[3770]: Stopping D-Bus User Message Bus...
Feb 05 19:16:17 wb9688-nuc6i3syh systemd[3770]: Stopping Virtual filesystem service...
Feb 05 19:16:17 wb9688-nuc6i3syh systemd[3770]: Stopping Sound Service...
Feb 05 19:16:17 wb9688-nuc6i3syh at-spi-bus-launcher[3864]: Invalid MIT-MAGIC-COOKIE-1 key
Feb 05 19:16:17 wb9688-nuc6i3syh systemd[3770]: gvfs-daemon.service: Main process exited, code=killed, status=15/TERM
Feb 05 19:16:17 wb9688-nuc6i3syh systemd[3770]: at-spi-dbus-bus.service: Succeeded.
Feb 05 19:16:17 wb9688-nuc6i3syh systemd[3770]: Stopped Accessibility services bus.
Feb 05 19:16:17 wb9688-nuc6i3syh systemd[3770]: run-user-1000-gvfs.mount: Succeeded.
Feb 05 19:16:17 wb9688-nuc6i3syh systemd[3770]: dbus.service: Succeeded.
Feb 05 19:16:17 wb9688-nuc6i3syh systemd[1]: run-user-1000-gvfs.mount: Succeeded.
Feb 05 19:16:17 wb9688-nuc6i3syh systemd[3770]: Stopped D-Bus User Message Bus.
Feb 05 19:16:17 wb9688-nuc6i3syh systemd[4509]: run-user-1000-gvfs.mount: Succeeded.
Feb 05 19:16:17 wb9688-nuc6i3syh systemd[3770]: gvfs-daemon.service: Succeeded.
Feb 05 19:16:17 wb9688-nuc6i3syh systemd[3770]: Stopped Virtual filesystem service.
Feb 05 19:16:17 wb9688-nuc6i3syh systemd[3770]: pulseaudio.service: Succeeded.
Feb 05 19:16:17 wb9688-nuc6i3syh systemd[3770]: Stopped Sound Service.
Feb 05 19:16:17 wb9688-nuc6i3syh systemd[3770]: Stopped target Basic System.
Feb 05 19:16:17 wb9688-nuc6i3syh systemd[3770]: Stopped target Paths.
Feb 05 19:16:17 wb9688-nuc6i3syh systemd[3770]: Stopped target Timers.
Feb 05 19:16:17 wb9688-nuc6i3syh systemd[3770]: Stopped target Sockets.
Feb 05 19:16:17 wb9688-nuc6i3syh systemd[3770]: dirmngr.socket: Succeeded.
Feb 05 19:16:17 wb9688-nuc6i3syh systemd[3770]: Closed GnuPG network certificate management daemon.
Feb 05 19:16:17 wb9688-nuc6i3syh systemd[3770]: dbus.socket: Succeeded.
Feb 05 19:16:17 wb9688-nuc6i3syh systemd[3770]: Closed D-Bus User Message Bus Socket.
Feb 05 19:16:17 wb9688-nuc6i3syh systemd[3770]: gpg-agent.socket: Succeeded.
Feb 05 19:16:17 wb9688-nuc6i3syh systemd[3770]: Closed GnuPG cryptographic agent and passphrase cache.
Feb 05 19:16:17 wb9688-nuc6i3syh systemd[3770]: gpg-agent-browser.socket: Succeeded.
Feb 05 19:16:17 wb9688-nuc6i3syh systemd[3770]: Closed GnuPG cryptographic agent and passphrase cache (access for web browsers).
Feb 05 19:16:17 wb9688-nuc6i3syh systemd[3770]: gpg-agent-ssh.socket: Succeeded.
Feb 05 19:16:17 wb9688-nuc6i3syh systemd[3770]: Closed GnuPG cryptographic agent (ssh-agent emulation).
Feb 05 19:16:17 wb9688-nuc6i3syh systemd[3770]: gpg-agent-extra.socket: Succeeded.
Feb 05 19:16:17 wb9688-nuc6i3syh systemd[3770]: Closed GnuPG cryptographic agent and passphrase cache (restricted).
Feb 05 19:16:17 wb9688-nuc6i3syh systemd[3770]: pulseaudio.socket: Succeeded.
Feb 05 19:16:17 wb9688-nuc6i3syh systemd[3770]: Closed Sound System.
Feb 05 19:16:17 wb9688-nuc6i3syh systemd[3770]: Reached target Shutdown.
Feb 05 19:16:17 wb9688-nuc6i3syh systemd[3770]: systemd-exit.service: Succeeded.
Feb 05 19:16:17 wb9688-nuc6i3syh systemd[3770]: Started Exit the Session.
Feb 05 19:16:17 wb9688-nuc6i3syh systemd[3771]: pam_unix(systemd-user:session): session closed for user wb9688
Feb 05 19:16:17 wb9688-nuc6i3syh systemd[3770]: Reached target Exit the Session.
Feb 05 19:16:17 wb9688-nuc6i3syh systemd[1]: [email protected]: Succeeded.
Feb 05 19:16:17 wb9688-nuc6i3syh systemd[1]: Stopped User Manager for UID 1000.
Feb 05 19:16:17 wb9688-nuc6i3syh systemd[1]: Stopping User Runtime Directory /run/user/1000...
Feb 05 19:16:17 wb9688-nuc6i3syh systemd[4509]: run-user-1000.mount: Succeeded.
Feb 05 19:16:17 wb9688-nuc6i3syh systemd[1]: run-user-1000.mount: Succeeded.
Feb 05 19:16:17 wb9688-nuc6i3syh systemd[1]: [email protected]: Succeeded.
Feb 05 19:16:17 wb9688-nuc6i3syh systemd[1]: Stopped User Runtime Directory /run/user/1000.
Feb 05 19:16:17 wb9688-nuc6i3syh systemd[1]: Removed slice User Slice of UID 1000.
那么，如果 DisplayPort 显示器断开连接，如何防止 LightDM 在解锁时崩溃呢？