GNOME Display Manager explained

GNOME Display Manager (GDM) is a display manager (a graphical login manager) 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. GDM 2.38.0 is the last version that features customization with themes; subsequent releases do not support themes.

Software architecture

GDM is a display manager that implements all significant features required for managing attached and remote displays. GDM was written from scratch and does not contain any XDM or X Consortium code.^[1]

Components

GDM comprises the following components:

• Chooser – a program used to select a remote host as the source for a remote display on the attached display (gdm-host-chooser)
• Greeter – the graphical login window (provided by GNOME Shell)
• Pluggable authentication module (PAM)
• X Display Manager Control Protocol (XDMCP)

Hidden features

Until version 2.22,^[2] GDM had a few Easter eggs, in the form of strings to be entered in the username box. These can be found in the source file "gui/guilogin.c", in a function named "evil".^[3]

• Dancing login – type "Start Dancing" to start, and "Stop Dancing" to stop.
  • (This requires the standard greeter ("GTK+ Greeter"), rather than the graphical one ("Themed Greeter")).
• "Gimme Random Cursor" – can be used repeatedly.
  • This changes the mouse cursor to a randomly selected 1 of 77 different "cursor fonts" as defined in the X11 specification.
• "Require Quarter" (or "Require Quater", for backward compatibility with a typo in the original),^[4] then log in normally – a dialog box that reads "Please insert 25 cents to log in." appears after entering the password. Clicking "OK" allows the login process to proceed as normal.

Queen of England

Some of the copyright notices of GDM refer to the "Queen of England", whom release announcements from version 2.2.1 also named as a maintainer.^[5] Subsequently, developers realised that the title "Queen of England" has not existed since the Acts of Union of 1707.^[6]

See also

1. getty – a non-graphical login program
2. LightDM
3. SDDM (KDE Plasma 5)
4. KDE Display Manager (KDE Plasma 4)

Notes and References

1. Web site: GDM documentation.
2. Web site: migrate gui to new config framework with a chainsaw . 2007-06-01 . 2014-04-26.
3. Web site: https://gitlab.gnome.org/GNOME/gdm/blob/gnome-2-20/gui/gdmlogin.c#L807 . gdm – guilogin.c . 2018-05-31 . 2018-08-09.
4. Web site: GDM commit ee8de912 . 5 March 2001 . 2009-08-26.
5. Web site: ANNOUNCE: GDM 2.2.1, the 'Just because you're not paranoid doesn't mean they're not after you' release . 4 May 2001 . Gdm2 was originally written by Martin K. Petersen , and is now maintained by the Queen of England..
6. Web site: ANNOUNCE: GDM 2.5.90.2 (unstable), the "Nose poking" release . 4 March 2004.