lightdm 服务启动失败、服务不见了、无反应

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

systemctl  start  lightdm

此时，命令无任何返回信息， 卡住完全不动

solutions：

请执行卸载下面的命令

yum groupremove  "GNOME Desktop"  -y

然后重试 start
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

正常情况 ：

Available Environment Groups:
   Minimal Install
   Compute Node
   Infrastructure Server
   File and Print Server
   MATE Desktop
   Basic Web Server
   Virtualization Host
   Server with GUI
   GNOME Desktop
   KDE Plasma Workspaces
   Development and Creative Workstation
Installed Groups:
   X Window System
   Xfce
Available Groups:
   Additional Development
   Backup Client

=======================================================

[root@VM_64_75_centos lightdm]#
[root@VM_64_75_centos lightdm]# systemctl status lightdm
* lightdm.service
   Loaded: not-found (Reason: No such file or directory)
   Active: failed (Result: start-limit) since Tue 2017-08-15 17:03:40 CST; 16min ago
 Main PID: 5065 (code=exited, status=1/FAILURE)

Aug 15 17:03:40 VM_64_75_centos systemd[1]: lightdm.service: main process exited, code=exited, status=1/FAILURE
Aug 15 17:03:40 VM_64_75_centos systemd[1]: Unit lightdm.service entered failed state.
Aug 15 17:03:40 VM_64_75_centos systemd[1]: lightdm.service failed.
Aug 15 17:03:40 VM_64_75_centos systemd[1]: lightdm.service holdoff time over, scheduling restart.
Aug 15 17:03:40 VM_64_75_centos systemd[1]: start request repeated too quickly for lightdm.service
Aug 15 17:03:40 VM_64_75_centos systemd[1]: Failed to start Light Display Manager.
Aug 15 17:03:40 VM_64_75_centos systemd[1]: Unit lightdm.service entered failed state.
Aug 15 17:03:40 VM_64_75_centos systemd[1]: lightdm.service failed.
[root@VM_64_75_centos lightdm]#

=================================================================

[root@VM_64_75_centos lightdm]# more lightdm.log
[+0.00s] DEBUG: Logging to /var/log/lightdm/lightdm.log
[+0.00s] DEBUG: Starting Light Display Manager 1.10.6, UID=0 PID=5044
[+0.00s] DEBUG: Loading configuration dirs from /usr/share/lightdm/lightdm.conf.d
[+0.00s] DEBUG: Loading configuration dirs from /usr/local/share/lightdm/lightdm.conf.d
[+0.00s] DEBUG: Loading configuration dirs from /etc/xdg/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: Registered seat module xlocal
[+0.00s] DEBUG: Registered seat module xremote
[+0.00s] DEBUG: Registered seat module unity
[+0.00s] DEBUG: Registered seat module surfaceflinger
[+0.00s] DEBUG: Adding default seat
[+0.00s] DEBUG: Seat: Starting
[+0.00s] DEBUG: Seat: Creating greeter session
[+0.00s] DEBUG: Seat: Creating display server of type x
[+0.00s] DEBUG: Using VT 1
[+0.00s] DEBUG: Seat: Starting local X display on VT 1
[+0.00s] DEBUG: DisplayServer x-0: Logging to /var/log/lightdm/x-0.log
[+0.00s] DEBUG: DisplayServer x-0: Writing X server authority to /var/run/lightdm/root/:0
[+0.00s] DEBUG: DisplayServer x-0: Launching X Server
[+0.00s] DEBUG: Launching process 5050: /usr/bin/X -background none :0 -seat seat0 -auth /var/run/lightdm/root/:0 -nolisten tcp vt1 -novtswitch
[+0.00s] DEBUG: DisplayServer x-0: Waiting for ready signal from X server :0
[+0.00s] DEBUG: Acquired bus name org.freedesktop.DisplayManager
[+0.01s] DEBUG: Registering seat with bus path /org/freedesktop/DisplayManager/Seat0
[+0.01s] DEBUG: Loading users from org.freedesktop.Accounts
[+0.01s] DEBUG: User /org/freedesktop/Accounts/User1001 added
[+0.01s] DEBUG: User /org/freedesktop/Accounts/User1600 added
[+0.07s] DEBUG: Got signal 10 from process 5050
[+0.07s] DEBUG: DisplayServer x-0: Got signal from X server :0
[+0.07s] DEBUG: DisplayServer x-0: Connecting to XServer :0
[+0.07s] DEBUG: Seat: Display server ready, starting session authentication
[+0.07s] DEBUG: Session pid=5060: Started with service 'lightdm-greeter', username 'lightdm'
[+0.08s] DEBUG: Session pid=5060: Authentication complete with return value 0: Success
[+0.08s] DEBUG: Seat: Session authenticated, running command
[+0.08s] DEBUG: Session pid=5060: Running command /usr/sbin/lightdm-gtk-greeter
[+0.08s] DEBUG: Creating shared data directory /var/lib/lightdm-data/lightdm
[+0.08s] DEBUG: Session pid=5060: Logging to /var/log/lightdm/x-0-greeter.log
[+0.08s] DEBUG: Activating VT 1
[+0.09s] DEBUG: Activating login1 session c19
[+0.10s] DEBUG: Session pid=5060: Greeter connected version=1.10.6
[+0.23s] DEBUG: Session pid=5060: Greeter closed communication channel
[+0.24s] DEBUG: Session pid=5060: Exited with return value 11
[+0.24s] DEBUG: Seat: Session stopped
[+0.24s] DEBUG: Seat: Stopping; failed to start a greeter
[+0.24s] DEBUG: Seat: Stopping
[+0.24s] DEBUG: Seat: Stopping display server
[+0.24s] DEBUG: Sending signal 15 to process 5050
[+0.29s] DEBUG: Process 5050 exited with return value 0
[+0.29s] DEBUG: DisplayServer x-0: X server stopped
[+0.29s] DEBUG: Releasing VT 1
[+0.29s] DEBUG: DisplayServer x-0: Removing X server authority /var/run/lightdm/root/:0
[+0.29s] DEBUG: Seat: Display server stopped
[+0.29s] DEBUG: Seat: Stopped
[+0.29s] DEBUG: Required seat has stopped
[+0.29s] DEBUG: Stopping display manager
[+0.29s] DEBUG: Display manager stopped
[+0.29s] DEBUG: Stopping daemon
[+0.30s] DEBUG: Exiting with return value 1

重新安装lightdm

================================

yum groupremove "X Window System"

yum groupremove -y xfce

yum remove -y lightdm

yum groupinstall "X Window System"

yum groupinstall -y xfce

yum install -y lightdm

=============================================
解决问题： ailed to restart lightdm.service: Unit not found.

重新安装lightdm之后发现 lightdm 不存在

=============================================

gdm 与 lightdm 冲突，二者智能选其一。

[root@VM_64_75_centos ~]#  systemctl start lightdm
Failed to start lightdm.service: Unit not found.
[root@VM_64_75_centos ~]#
[root@VM_64_75_centos ~]#
[root@VM_64_75_centos ~]# systemctl restart lightdm
Failed to restart lightdm.service: Unit not found.
[root@VM_64_75_centos ~]#
[root@VM_64_75_centos ~]# systemctl list-units|grep dm
  sys-devices-virtual-block-dm\x2d0.device                          loaded    active plugged   /sys/devices/virtual/block/dm-0
* lightdm.service                                                   not-found failed failed    lightdm.service
  lvm2-monitor.service                                              loaded    active exited    Monitoring of LVM2 mirrors, snapshots etc. using dmeventd or progress polling
  rhel-dmesg.service                                                loaded    active exited    Dump dmesg to /var/log/dmesg
  system-selinux\x2dpolicy\x2dmigrate\x2dlocal\x2dchanges.slice     loaded    active active    system-selinux\x2dpolicy\x2dmigrate\x2dlocal\x2dchanges.slice
  dm-event.socket                                                   loaded    active listening Device-mapper event daemon FIFOs
[root@VM_64_75_centos ~]#
[root@VM_64_75_centos ~]#
[root@VM_64_75_centos ~]#
[root@VM_64_75_centos ~]# systemctl list-unit-files|grep dm
dm-event.service                              disabled
gdm.service                                   enabled
initrd-udevadm-cleanup-db.service             static 
lightdm.service                               disabled
rdma.service                                  disabled
rhel-dmesg.service                            disabled
rhel-loadmodules.service                      static 
dm-event.socket                               enabled
[root@VM_64_75_centos ~]# systemctl disable gdm.service
Removed symlink /etc/systemd/system/display-manager.service.
[root@VM_64_75_centos ~]#
[root@VM_64_75_centos ~]#
[root@VM_64_75_centos ~]# systemctl list-unit-files|grep dm
dm-event.service                              disabled
gdm.service                                   disabled
initrd-udevadm-cleanup-db.service             static 
lightdm.service                               disabled
rdma.service                                  disabled
rhel-dmesg.service                            disabled
rhel-loadmodules.service                      static 
dm-event.socket                               enabled
[root@VM_64_75_centos ~]# systemctl enable lightdm.service
Created symlink from /etc/systemd/system/display-manager.service to /usr/lib/systemd/system/lightdm.service.
[root@VM_64_75_centos ~]#
[root@VM_64_75_centos ~]#
[root@VM_64_75_centos ~]#
[root@VM_64_75_centos ~]#
[root@VM_64_75_centos ~]# systemctl list-units|grep dm
  sys-devices-virtual-block-dm\x2d0.device                          loaded active plugged   /sys/devices/virtual/block/dm-0
  lvm2-monitor.service                                              loaded active exited    Monitoring of LVM2 mirrors, snapshots etc. using dmeventd or progress polling
  rhel-dmesg.service                                                loaded active exited    Dump dmesg to /var/log/dmesg
  system-selinux\x2dpolicy\x2dmigrate\x2dlocal\x2dchanges.slice     loaded active active    system-selinux\x2dpolicy\x2dmigrate\x2dlocal\x2dchanges.slice
  dm-event.socket                                                   loaded active listening Device-mapper event daemon FIFOs
[root@VM_64_75_centos ~]# systemctl restart lightdm
[root@VM_64_75_centos ~]# systemctl  status lightdm
* lightdm.service - Light Display Manager
   Loaded: loaded (/usr/lib/systemd/system/lightdm.service; enabled; vendor preset: enabled)
   Active: active (running) since Tue 2017-08-15 17:44:02 CST; 16s ago
     Docs: man:lightdm(1)
 Main PID: 9898 (lightdm)
   CGroup: /system.slice/lightdm.service
           |-9898 /usr/sbin/lightdm
           |-9904 /usr/bin/X -background none :0 -seat seat0 -auth /var/run/lightdm/root/:0 -nolisten tcp vt1 -novtswitch
           `-9934 lightdm --session-child 12 19

Aug 15 17:44:02 VM_64_75_centos systemd[1]: Starting Light Display Manager...
Aug 15 17:44:02 VM_64_75_centos systemd[1]: Started Light Display Manager.
Aug 15 17:44:02 VM_64_75_centos lightdm[9914]: pam_unix(lightdm-greeter:session): session opened for user lightdm by (uid=0)
[root@VM_64_75_centos ~]#