GNOME/GDM

As part of the GNOME desktop suite, the GNOME Display Manager (GDM) Article description::is the daemon responsible for launching graphical display sessions via the [[Xorg display server or the directly via Wayland display protocol.]]

Debugging
To enable debugging, edit the following configuration file:

On systems running systemd, this will configure GDM to write verbose output to the journal. Be sure to disable debugging when finished resolving any issues to save space in the journal.

See upstream's debug documentation for more details on debugging GDM.

GDM and Optimus
See the GDM section of the NVIDIA Optimus article when using GDM on platforms utilizing NVIDIA Optimus.

Enable tap to click in GDM
Tap to click is disabled by default in GDM's environment. Enabling this feature requires setting GNOME option for the  user.

Grant permissions for to access the X server:

Then set the gsettings configuration value as the gdm user to enable tap to click:

The new setting will take effect after restarting the GDM service.

GDM crashes when attempting to launch a GNOME Wayland session
Problem: GDM is crashing when attempting to launch a GNOME Wayland session. Known to affect at least gdm-3.32.0.

Solution: This is most likely occurring because the NVIDIA kernel module is being loaded by the kernel and subsequently detected by udev - even if it not being used by the graphics stack. The udev rule (see ) is shipped with GDM. Even if the system is not actively using the NVIDIA driver or NVIDIA hardware to render graphics, the rule will still trigger the executable. This writes a configuration file to which is read by GDM at start time and disables support for Wayland sessions.

There are a few solutions to this problem:


 * 1) Uninstall the  package and remove the installed NVIDIA kernel modules. This is most likely the easiest solution, since it will remove the NVIDIA kernel module that triggers the udev rule  and prevent it from returning.
 * 2) Blacklist the NVIDIA kernel module from loading. This can is performed different ways: kernel command-line parameters via the secondary bootloader (GRUB2, systemd-boot, etc.) or adding a blacklist configuration file via modprobe.d.
 * 3) System administrators that want to keep the NVIDIA binary blob available for other desktop environments, but want to launch GNOME on Wayland and follow this last solution. It is simplest to manually editing the offending part of the udev rule so that gdm-disable-wayland cannot create the custom configuration file. To be safe, review Xorg's configuration files in the  directory to be sure NVIDIA is not being set as the primary Xorg driver. It is also a good idea to review the  to double check. Simply comment out the last line:

GDM produces an all-black screen when more than one video driver is loaded
One of the benefits of Wayland is the ability to run multi-GPU multi-head sessions. It is also possible for users to do this with multiple GPU drivers (e.g. running a modern AMDGPU card and an older radeon card in the same machine). This setup will work fine as long as modules are loaded in the correct order; if automatic configuration changes the module load order for some reason, it's possible that the older driver will load first and GDM will attempt to open a Xorg session, which may fail.

If this happens, users are able to force the kernel to load modules in a specific order by adapting the following procedure to your hardware (at least for systemd users): First, blacklist every GPU driver module except the one you want to load first by modifying /etc/modprobe.d/blacklist.conf

Next, load other drivers you may need in /etc/modules-load.d/gpu.conf

External resources

 * https://help.gnome.org/admin/gdm/stable/ - Upstream's administration guide