GDM

GDM, short for GNOME Display Manager, is the display manager used by the GNOME desktop environment. A display manager is the component responsible for handling graphical logins, starting user sessions, and managing access to the graphical server. GDM runs as a system daemon and coordinates with the display server (X11 or Wayland) to present a login screen and to initiate a user session after successful authentication.

The login screen, or greeter, presents available user accounts, accepts credentials, and offers a session selector to choose a desktop environment or session type. It support features such as automatic login and timed login, and can be configured to enable or disable remote login options. Authentication is handled through PAM and can integrate with accountsservice for user information and policy.

GDM is commonly packaged as gdm or gdm3, depending on the distribution. It is typically controlled by systemd as a service. Configuration is usually done in /etc/gdm/custom.conf, where administrators can enable automatic login, set login greeter preferences, or adjust security and accessibility options. GDM supports both Wayland and Xorg sessions, and may allow choosing between them at the login screen.

Despite its GNOME focus, GDM can be used with other desktop environments, although it is optimized for GNOME’s session structure. It is one of several display managers available for Linux and Unix-like systems, alongside LightDM and SDDM.