DESCRIPTIONgdm3 is the equivalent of xdm(1x) or wdm(1x), but uses the GNOME libraries to provide a GNOME look-and-feel. It provides the GNOME equivalent of a ``login:'' prompt.
gdm3 reads /etc/gdm3/daemon.conf for its configuration. For each local display, gdm starts an X server and runs a minimal GNOME session including a graphical greeter. If configured so, the main gdm process also listens for XDMCP requests from remote displays. These requests can either be direct, causing gdm3 to start a session on the remote display, or indirect, causing a chooser to be opened.
When managing a display, gdm3 attempts to execute /etc/gdm3/Init/display, or /etc/gdm3/Init/Default if that does not exist. When a user logs in, gdm3 first attempts /etc/gdm3/PreSession/display (or /etc/gdm3/PreSession/Default), and then one of the sessions defined in /usr/share/xsessions. When the session has completed, gdm attempts to run /etc/gdm3/PostSession/display, or /etc/gdm3/PostSession/Default.
gdm3 maintains information about the displays it is managing in /var/lib/gdm3. This includes xauth information, so this directory is not readable to normal users.
gdm3 uses PAM to perform authentication using the config file /etc/pam.d/gdm3.
Upon session startup, GDM sets the XAUTHORITY environment variable to a
session-specific file in /var/run/gdm3.
Applications and scripts that assume this file is set to ~/.Xauthority will not work. To access the display you need both DISPLAY and XAUTHORITY variables.