X display manager - Definition and Overview

In computing, in the X Window System, an X display manager keeps the X server process alive on the X server machine, connecting it to a physical screen and serving a login prompt on this screen when there are no clients running.

The display manager communicates using XDMCP (X Display Manager Control Protocol). It listens to UDP port 177 and will respond to QUERY and BROADCAST_QUERY requests by sending a WILLING packet to the originator.

When using an X server running on a standalone X terminal, a list of connectable client hosts is presented (an XDMCP Chooser). This list of can be a predefined list of hosts and their respective network addresses or a list that the XDMCP server in turn obtains by a network broadcast, which in effect most often mean that the list of hosts presented is limited to the local TCP/IP subnet. It is not uncommon for the XDMCP server to present itself in this list. When the user selects a host from the list, the X server running on the local machine will connect to the remote computer's X display manager.

XDM (X Window Display Manager) is the basic display manager supplied with X. Others include GDM (GNOME), KDM (KDE), WINGs Display Manager (using the WINGs widget set used in Window Maker) and entrance (using the architecture used in Enlightenment v.17).

See also

• X Window System protocols and architecture

External links

• XDMCP documentation (ftp://ftp.x.org/pub/R6.4/xc/doc/hardcopy/XDMCP/xdmcp.PS.gz) from the X.Org repository (compressed PostScript)
• Linux XDMCP HOWTO (http://www.tldp.org/HOWTO/XDMCP-HOWTO/index.html)