GDM (the GNOME Display Manager) is a display manager (a graphical login program) for the windowing systems X11 and Wayland.The X Window System by default uses the XDM display manager. However, resolving XDM configuration issues typically involves editing a configuration file. GDM allows users to customize or troubleshoot settings without having to resort to a command line. Users can pick their session type on a per-login basis.