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Chapter 5. GDM

GDM is the GNOME Display Manager, which provides a graphical login environment. After the transition from GNOME 2 to GNOME 3, configuring GDM is only possible through systemd as it no longer supports other init systems.
the gdm package
The gdm package has replaced xorg-x11-xdm, which provided a legacy display login manager for the X Window System. As mentioned before, the gdm package provides the graphical login screen, shown shortly after boot up, log out, and when user-switching.
GDM and logind
GDM now uses logind for defining and tracking users. For more information, see Chapter 2, logind. System administrators can also set up automatic login manually in the GDM custom configuration file: /etc/gdm/custom.conf.
custom.conf
GDM configuration is now found in /etc/gdm/custom.conf. However for backwards compatibility, if /etc/gdm/gdm.conf is found it will be used instead of custom.conf. When upgrading, Red Hat recommends removing your old gdm.conf file and migrating any custom configuration to custom.conf.

Getting More Information

For more information on GDM, see Section 14.1, “What Is GDM?”.
For information on configuring and managing user sessions, see Section 14.3, “User Sessions”.
For information on customizing the login screen appearance, see Section 10.4, “Customizing the Login Screen”.