我有一台在 Thinkpad T430s 上运行的标准 Ubuntu 18.04 机器。我使用 gdm3 作为我的显示管理器。昨天 gdm3 停止工作了。我安装了更新，关闭了机器，下次我再次启动它时，在启动时 Ubuntu 徽标消失后，屏幕仍然黑着。
幸运的是，我可以通过安装 xdm 的终端访问终端ALT+CTRL+F1，将其配置为默认显示管理器并卸载 gdm3。虽然 xdm 运行良好，但我对它的可用性并不满意，因此安装了 SLiM。SLiM 开箱即用。
今天，SLiM 和我安装的其他显示管理器（xdm、lightDM、gdm3）都不起作用。此外，当我通过终端登录以手动启动 X-Server 时，它崩溃了。在我startx第二次输入命令后，X-Server 终于启动了。
我不知道是什么原因导致了这个问题，我很感激任何线索。
/var/log/slim.log：
slim: waiting for X server to begin accepting connections.
slim: waiting for X server to shut down.
slim: waiting for X server to begin accepting connections.
slim: waiting for X server to shut down.
slim: waiting for X server to begin accepting connections.
slim: waiting for X server to shut down.
slim: waiting for X server to begin accepting connections.
slim: unexpected signal 15
slim: connection to X server lost.
slim: waiting for X server to shut down
slim: waiting for X server to begin accepting connections.
slim: waiting for X server to shut down.
slim: waiting for X server to begin accepting connections.
slim: pam_authentication(): Authentication failure
slim: waiting for X server to shut down.
slim: waiting for X server to begin accepting connections.
slim: pam_authentication(): Authentication failure
slim: unexpected signal 15
slim: connection to X server lost.
slim: waiting for X server to shut down
slim: waiting for X server to begin accepting connections.
slim: waiting for X server to begin accepting connections.
slim: pam_authentication(): Authentication failure
slim: unexpected signal 15
slim: connection to X server lost.
slim: waiting for X server to shut down
slim: waiting for X server to begin accepting connections.
slim: unexpected signal 15
slim: connection to X server lost.
slim: waiting for X server to shut down
/var/log/xdm.log：
Tue Jul 10 15:17:54 2018 xdm info (pid 1350): Starting
Tue Jul 10 15:17:54 2018 xdm info (pid 1350): Starting X server on :0
X.Org X Server 1.19.6
Release Date: 2017-12-20
X Protocol Version 11, Revision 0
Build Operating System: Linux 4.4.0-119-generic x86_64 Ubuntu
Current Operating System: Linux philipp-ThinkPad-T430s 4.15.0-24-generic #26-Ubuntu SMP Wed Jun 13 08:44:47 UTC 2018 x86_64
Kernel command line: BOOT_IMAGE=/boot/vmlinuz-4.15.0-24-generic root=UUID=f99351c7-ae2a-4ce1-b539-e4ed1f555a19 ro quiet splash vt.handoff=1
Build Date: 13 April 2018 08:07:36PM
xorg-server 2:1.19.6-1ubuntu4 (For technical support please see http://www.ubuntu.com/support)
Current version of pixman: 0.34.0
Before reporting problems, check http://wiki.x.org
to make sure that you have the latest version.
Markers: (--) probed, (**) from config file, (==) default setting,
(++) from command line, (!!) notice, (II) informational,
(WW) warning, (EE) error, (NI) not implemented, (??) unknown.
(==) Log file: "/var/log/Xorg.0.log", Time: Tue Jul 10 15:17:54 2018
(==) Using system config directory "/usr/share/X11/xorg.conf.d"
Tue Jul 10 15:17:56 2018 xdm info (pid 2381): sourcing /etc/X11/xdm/Xsetup
Tue Jul 10 15:18:00 2018 xdm info (pid 2381): sourcing /etc/X11/xdm/Xstartup
Tue Jul 10 15:18:00 2018 xdm info (pid 2514): executing session /etc/X11/xdm/Xsession
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Jul 10 15:21:57 2018 xdm info (pid 1215): Starting
Tue Jul 10 15:21:57 2018 xdm info (pid 1215): Starting X server on :0
X.Org X Server 1.19.6
Release Date: 2017-12-20
X Protocol Version 11, Revision 0
Build Operating System: Linux 4.4.0-119-generic x86_64 Ubuntu
Current Operating System: Linux philipp-ThinkPad-T430s 4.15.0-24-generic #26-Ubuntu SMP Wed Jun 13 08:44:47 UTC 2018 x86_64
Kernel command line: BOOT_IMAGE=/boot/vmlinuz-4.15.0-24-generic root=UUID=f99351c7-ae2a-4ce1-b539-e4ed1f555a19 ro quiet splash vt.handoff=1
Build Date: 13 April 2018 08:07:36PM
xorg-server 2:1.19.6-1ubuntu4 (For technical support please see http://www.ubuntu.com/support)
Current version of pixman: 0.34.0
Before reporting problems, check http://wiki.x.org
to make sure that you have the latest version.
Markers: (--) probed, (**) from config file, (==) default setting,
(++) from command line, (!!) notice, (II) informational,
(WW) warning, (EE) error, (NI) not implemented, (??) unknown.
(==) Log file: "/var/log/Xorg.0.log", Time: Tue Jul 10 15:21:57 2018
(==) Using system config directory "/usr/share/X11/xorg.conf.d"
Tue Jul 10 15:21:58 2018 xdm info (pid 2403): sourcing /etc/X11/xdm/Xsetup
Tue Jul 10 15:22:02 2018 xdm info (pid 2403): sourcing /etc/X11/xdm/Xstartup
Tue Jul 10 15:22:02 2018 xdm info (pid 2445): executing session /etc/X11/xdm/Xsession
(II) AIGLX: Suspending AIGLX clients for VT switch
Tue Jul 10 15:39:14 2018 xdm error (pid 1215): Unknown session exit code 256 from process 2403
Tue Jul 10 15:39:14 2018 xdm info (pid 1215): Shutting down
(II) Server terminated successfully (0). Closing log file.
Tue Jul 10 15:39:14 2018 xdm info (pid 1215): Exiting
Tue Jul 10 15:39:29 2018 xdm info (pid 1315): Starting
Tue Jul 10 15:39:29 2018 xdm info (pid 1315): Starting X server on :0
X.Org X Server 1.19.6
Release Date: 2017-12-20
X Protocol Version 11, Revision 0
Build Operating System: Linux 4.4.0-119-generic x86_64 Ubuntu
Current Operating System: Linux philipp-ThinkPad-T430s 4.15.0-24-generic #26-Ubuntu SMP Wed Jun 13 08:44:47 UTC 2018 x86_64
Kernel command line: BOOT_IMAGE=/boot/vmlinuz-4.15.0-24-generic root=UUID=f99351c7-ae2a-4ce1-b539-e4ed1f555a19 ro quiet splash vt.handoff=1
Build Date: 13 April 2018 08:07:36PM
xorg-server 2:1.19.6-1ubuntu4 (For technical support please see http://www.ubuntu.com/support)
Current version of pixman: 0.34.0
Before reporting problems, check http://wiki.x.org
to make sure that you have the latest version.
Markers: (--) probed, (**) from config file, (==) default setting,
(++) from command line, (!!) notice, (II) informational,
(WW) warning, (EE) error, (NI) not implemented, (??) unknown.
(==) Log file: "/var/log/Xorg.0.log", Time: Tue Jul 10 15:39:29 2018
(==) Using system config directory "/usr/share/X11/xorg.conf.d"
Tue Jul 10 15:39:31 2018 xdm info (pid 2406): sourcing /etc/X11/xdm/Xsetup
Tue Jul 10 15:39:35 2018 xdm info (pid 2406): sourcing /etc/X11/xdm/Xstartup
Tue Jul 10 15:39:35 2018 xdm info (pid 2539): executing session /etc/X11/xdm/Xsession
Tue Jul 10 15:42:50 2018 xdm info (pid 2406): sourcing /etc/X11/xdm/Xreset
Tue Jul 10 15:42:50 2018 xdm info (pid 1315): Starting X server on :0
Tue Jul 10 15:42:51 2018 xdm info (pid 5898): sourcing /etc/X11/xdm/Xsetup
Tue Jul 10 15:42:56 2018 xdm info (pid 5898): sourcing /etc/X11/xdm/Xstartup
Tue Jul 10 15:42:56 2018 xdm info (pid 5941): executing session /etc/X11/xdm/Xsession
Tue Jul 10 15:43:11 2018 xdm info (pid 1315): Shutting down
Tue Jul 10 15:43:11 2018 xdm error (pid 1315): Unknown session exit code 256 from process 5898
(II) Server terminated successfully (0). Closing log file.
Tue Jul 10 15:43:12 2018 xdm info (pid 1315): Exiting
//编辑：可以找到/var/log/Xorg.0.log这里