XDMCP

A screenshot of the XDM login screen.

XDMCP (acronym for "X Display Manager Control Protocol", "Display Manager Control Protocol X" in Spanish) is a protocol used in networks to communicate a server computer running an operating system with an X-based window manager, with other clients that will connect to it for interactive purposes..

An X Display Manager keeps X server processes running on it, connecting it to a physical display and providing a dialog allowing everyone to log in to it. computers that require it. It listens to the User Datagram Protocol (UDP) on port 177 and responds to QUERY and BROADCAST_QUERY type requests by sending a WILLING type packet to the host that contacted him.

When an X server runs in a standalone X terminal, it displays a list of connectable clients (an XDMCP Chooser). This list may be composed of:

• A predefined list of machines and their respective network addresses;.
• A list that the XDMCP in turn gets through a broadcast request, which normally matches the list of local TCP/IP machines.

It is common for the XDMCP server to show itself in the list. When the user selects a host from the list, the X server running on the local host connects to the X display manager on the remote host.

X provides XDM (X Window Display Manager) as the primary display manager. Other examples of screen managers are:

• GDM (GNOME)
• KDM (KDE)
• WINGs Display Manager
• Entrance (using the architecture used in Enlightenment v.17).