X display manager

In this condition, the DM realizes in the X Window System the functionality of getty and login on character-mode terminals.

X11 Release 3 introduced display managers in October 1988 with the aim of supporting the standalone X terminals, just coming onto the market.

This first version, written by Keith Packard of the MIT X Consortium, had several limitations, the most notable of which was that it could not detect when users switched X terminals off and on.

Thus every time a user switched a terminal off and on, the system administrator had to send a SIGHUP signal to XDM to instruct it to rescan Xservers.

In the X Window System paradigm, the server runs on the computer providing the display and input devices.

A server can connect, using the XDMCP protocol, to a display manager running on another computer, requesting it to start the session.

Most implementations enable such a list to contain: When the user selects a host from the list, the XDMCP Chooser running on the local machine will send a message to the selected remote computer's display manager and instruct it to connect the X server on the local computer or terminal.

A login screen shown by the SDDM display manager.
In the X Window System, the X server runs on the computer in front of the user. The X server may connect to a display manager running on another computer, starting a session which may comprise a variety of programs running on that other computer. Relative to X server the XDM is a client. See client–server separation in X11.