Editing X display manager (section)

==Local and remote display management==
A display manager can run on the same computer where the user sits—starting one or more X servers, displaying the login screen at the beginning and (optionally) every time the user logs out—or on a remote one, working according to the XDMCP protocol.

[[Image:Xserver and display manager.svg|thumb|400px|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 [[X Window System|client–server separation]] in X11.]]

The XDMCP protocol mandates that the X server starts autonomously and connects to the display manager. 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. In this case, the X server acts as a graphical [[telnet]] client while the display manager acts like a telnet server: users start programs from the computer running the display manager, while their input and output take place on the computer where the server (and the user) sits.

An administrator can typically configure an '''XDMCP Chooser''' program running on the local computer or X terminal to connect to a specific host's X display manager or to display a list of suitable hosts that the user can choose from. Most implementations enable such a list to contain:
# a predefined set of hosts and their respective network addresses, and/or
# a set of hosts (on the local [[Internet protocol suite|TCP/IP]] [[subnetwork|subnet]]) that the XDMCP Chooser determines by a [[broadcast domain|network broadcast]] to the available display managers.

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.