经过几次更新后，我的系统lightdm似乎出现了问题（无法进行会话lightdm，总是在启动时进入低图形模式）。如果我选择gdm它，它就可以工作。但我希望恢复 lightdm，因为我真的不喜欢lightdm-gtk-greeter。
lightdm --test-mode --debug给出
[+0.00s] DEBUG: Logging to /home/andreas/.cache/lightdm/log/lightdm.log
[+0.00s] DEBUG: Starting Light Display Manager 1.16.6, UID=1000 PID=11764
[+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/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 from /usr/share/lightdm/lightdm.conf.d/60-gnome.conf
[+0.00s] DEBUG: Loading configuration from /usr/share/lightdm/lightdm.conf.d/60-lightdm-gtk-greeter.conf
[+0.00s] DEBUG: Loading configuration from /usr/share/lightdm/lightdm.conf.d/90-nvidia.conf
[+0.00s] DEBUG: [SeatDefaults] is now called [Seat:*], please update this configuration
[+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 /usr/share/ubuntu/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-ubuntu/lightdm/lightdm.conf.d
[+0.00s] DEBUG: Loading configuration from /etc/lightdm/lightdm.conf
[+0.00s] DEBUG: [SeatDefaults] is now called [Seat:*], please update this configuration
[+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
[+0.02s] DEBUG: Monitoring logind for seats
[+0.02s] DEBUG: New seat added from logind: seat0
[+0.02s] DEBUG: Seat seat0: Loading properties from config section Seat:*
[+0.02s] DEBUG: Seat seat0: Starting
[+0.02s] DEBUG: Seat seat0: Creating greeter session
[+0.02s] DEBUG: Loading users from org.freedesktop.Accounts
[+0.02s] DEBUG: User /org/freedesktop/Accounts/User1000 added
[+0.02s] DEBUG: Seat seat0: Creating display server of type x
[+0.03s] DEBUG: Seat seat0: Starting local X display
[+0.03s] DEBUG: DisplayServer x-1: Logging to /home/andreas/.cache/lightdm/log/x-1.log
[+0.03s] DEBUG: DisplayServer x-1: Writing X server authority to /home/andreas/.cache/lightdm/run/root/:1
[+0.03s] DEBUG: DisplayServer x-1: Launching X Server
[+0.03s] DEBUG: Launching process 11769: /usr/bin/Xephyr :1 -seat seat0 -auth /home/andreas/.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
[+0.04s] DEBUG: Process 11769 exited with return value 1
[+0.04s] DEBUG: DisplayServer x-1: X server stopped
[+0.04s] DEBUG: DisplayServer x-1: Removing X server authority /home/andreas/.cache/lightdm/run/root/:1
[+0.04s] DEBUG: Seat seat0: Display server stopped
[+0.04s] DEBUG: Launching process 11770: /sbin/prime-switch
Warning: writing to /var/log/gpu-manager.log failed (Permission denied)
log_file: /var/log/gpu-manager.log
last_boot_file: /var/lib/ubuntu-drivers-common/last_gfx_boot
new_boot_file: /var/lib/ubuntu-drivers-common/last_gfx_boot
/etc/modprobe.d is not a file
grep dmesg status 256
dmesg status 256 == 0? No
/etc/modprobe.d is not a file
/etc/modprobe.d is not a file
/etc/modprobe.d is not a file
Is nvidia loaded? yes
Was nvidia unloaded? no
Is nvidia blacklisted? no
Is fglrx loaded? no
Was fglrx unloaded? no
Is fglrx blacklisted? no
Is intel loaded? yes
Is radeon loaded? no
Is radeon blacklisted? no
Is nouveau loaded? no
Is nouveau blacklisted? yes
Is fglrx kernel module available? no
Is nvidia kernel module available? yes
Vendor/Device Id: 8086:a16
BusID "PCI:0@0:2:0"
Is boot vga? yes
Vendor/Device Id: 10de:1290
BusID "PCI:9@0:0:0"
Is boot vga? no
Skipping "/dev/dri/card1", driven by "nvidia-drm"
Skipping "/dev/dri/card0", driven by "i915"
Skipping "/dev/dri/card1", driven by "nvidia-drm"
Skipping "/dev/dri/card0", driven by "i915"
Skipping "/dev/dri/card1", driven by "nvidia-drm"
Found "/dev/dri/card0", driven by "i915"
output 0:
eDP connector
Number of connected outputs for /dev/dri/card0: 1
Does it require offloading? yes
last cards number = 2
Has amd? no
Has intel? yes
Has nvidia? yes
How many cards? 2
Has the system changed? No
main_arch_path x86_64-linux-gnu, other_arch_path i386-linux-gnu
update-alternatives: error: no alternatives for x86_64-linux-gnu_gfxcore_conf
Current alternative: /usr/lib/nvidia-358-prime/ld.so.conf
Current core alternative: (null)
Is nvidia enabled? no
Is fglrx enabled? no
Is mesa enabled? no
Is pxpress enabled? no
Is prime enabled? yes
Is nvidia available? yes
Is fglrx available? no
Is fglrx-core available? no
Is mesa available? yes
Is pxpress available? no
Is prime available? yes
Intel IGP detected
Intel hybrid system
Nvidia driver version 358.16 detected
Removing xorg.conf. Path: /etc/X11/xorg.conf
Moved /etc/X11/xorg.conf to /etc/X11/xorg.conf.01122016
Powering off the discrete card
initctl: Name "com.ubuntu.Upstart" does not exist
Unloading nvidia-uvm with "no" parameters
rmmod: ERROR: Module nvidia_uvm is not currently loaded
Unloading nvidia with "no" parameters
rmmod: ERROR: Module nvidia is in use by: nvidia_modeset
[+0.08s] DEBUG: Process 11770 exited with return value 0
[+0.08s] DEBUG: Seat seat0: Exit status of /sbin/prime-switch: 0
[+0.08s] DEBUG: Seat seat0: Stopping; greeter display server failed to start
[+0.08s] DEBUG: Seat seat0: Stopping
[+0.08s] DEBUG: Seat seat0: Stopping session
[+0.08s] DEBUG: Seat seat0: Session stopped
[+0.08s] DEBUG: Seat seat0: Stopped
[+0.08s] DEBUG: Required seat has stopped
[+0.08s] DEBUG: Stopping display manager
[+0.08s] DEBUG: Display manager stopped
[+0.08s] DEBUG: Stopping daemon
[+0.08s] DEBUG: Seat seat0: Stopping session
[+0.08s] DEBUG: Exiting with return value 1
有人有主意吗？
答案1
经过两天的尝试，我自己找到了答案：
问题是.Xauthoritylightdm 文件不知为何丢失了。使用 创建它touch /var/lib/lightdm/.Xauthority并sudo chown lightdm:lightdm /var/lib/lightdm/.Xauthority修复了该问题。
答案2
从 15.04 升级到 15.10 后，我的桌面拒绝启动。
在我的情况下，该文件夹/var/lib/lightdm根本不存在，而且我发现它也不是 lightdm 包的一部分。创建该文件夹并将所有权转让给 lightdm 为我解决了这个问题：
mkdir /var/lib/lightdm
chown -R lightdm /var/lib/lightdm