This post guides you on fixing the error – Failed to Start Light Display Manager Error in Linux systems.
I know it’s not a good feeling when you expect something to come up on the screen and suddenly face this particular error. It is uncomfortable because you are lost in a terminal and unsure of what to do.
If you follow some steps, it’s easier to fix. So, let’s try to fix it.
Table of Contents
How to Fix – Failed to Start Light Display Manager Error
Why this error?
This error comes from the lightdm package, a popular Linux system display manager. It is likely caused by any action you may have taken before this error. More likely, it is caused by incorrect package updates or removing specific lightdm related packages or incorrect configurations of lightdm.
The display manager enables the login screen by communicating with the X11 server; failing to do so, the system stalls at the prompt and sometimes with a black screen.
How to Fix
As it may have been caused by multiple failure points, the solution may differ. Here I am outlining some of the fixes that may help you troubleshoot.
When you are stuck at the above screen, press CTRL+ALT+F2 to reach the console mode.
Then log in using any admin id and password. You can log in using your usual user id, and when required, you can provide the sudo password as well.
Firstly, check whether anything wrong with the lightdm systemd service.
systemctl status lightdm
If it gives you the status GREEN, then something else is broken.
Next, try to run the following command to start lightdm as test mode with debugging switch. This would try to launch lightdm and show you any errors or warnings.
lightdm --test-mode --debug
For this example, as you can see below – it successfully loads everything, but in the end, it cannot find the greeter. The greeter is a graphical login window where you enter your user id and password. And for this case, somehow, the greeter is corrupted.
So, the obvious corrective step is reinstalling the greeter and enabling the lightdm systemd service. You can use your distribution’s package manager to install the greeter.
For this guide, I am using Arch Linux hence I ran the following to re-install the lightdm-gtk-greeter –
pacman -S lightdm-gtk-greeter
Then enable the systemd service for lightdm, just in case.
systemctl enable lightdm
And then reboot –
systemctl reboot
If all goes well, this error should disappear, and you should get your login screen back.
Other Solutions
If the above steps do not work, you might also want to review the following troubleshooting options. These may work.
- Xorg server is corrupted or not installed. Hence, lightdm is not able to communicate with Xorg. Reinstalling xorg package would help. You can reinstall Arch Linux just by using
pacman -S xorg. - Sometimes the
lightdm-gtk-greeter-settingspackage misconfiguration causes this error. So reinstallinglightdm-gtk-greeter-settingscan help as well. - It is always recommended to check whether you have the lightdm service enabled via systemd.
- In the end, check the log of debug mode command carefully. You will find the possible cause of this problem.
- Verify the lightdm log file and Xorg log file in the following path for any errors or warnings. The lightdm log file:
/var/log/lightdm/lightdm.log. And the Xorg log file/var/log/lightdm/x-0.org. - If you have an advanced system that boots in superfast mode, then lightdm and graphics drivers may run into race conditions. The lightdm service may start before the Kernel loads the graphics drivers. If this is the case, you may try to add the following lines in the
/etc/lightdm/lightdm.conffile under[lightDM]section.
[LightDM]
logind-check-graphical=true
Historically, Nvidia driver updates may cause issues with Xorg and lightdm. As lightdm depends on Xorg to work properly, it might be necessary to fix Xorg for errors. The following commands you may use to reconfigure Xorg after removing the Nvidia driver.
cp /etc/X11/xorg.conf /etc/X11/xorg_backup.conf
sudo Xorg -configure
cp /root/xorg.conf.new /etc/X11/xorg.conf
startx
Closing Notes
This error is more frequent in Arch Linux and its derivatives, such as Manjaro, Arco Linux, etc. I hope the above troubleshooting steps help you to get back to your login screen and your system. Let me know in the comment box below if it helps.
