Technical data

19
Configuring XDMCP-Compatible X Displays
The X Window System, developed by the Massachusetts Institute of Technology,
is a network-based graphics window system based on the client/server application
model. The X protocol, through which the client and server communicate, runs on
UNIX domain sockets, TCP/IP, or DECnet. This means that an X display on one
system can display information output from an application running on another
system in the network.
An X display is a graphic output device that is known by The X Display Manager
(XDM), such as:
• An X terminal
• A workstation that has the X Window System software installed and
configured
• A PC running Windows or Windows NT and some X Window System software,
such as eXcursion or Exceed
This chapter reviews key concepts, discusses how to configure an XDMCP-
compatible X display using the TCP/IP Services XDM server, and covers the
following topics:
• XDMCP queries (Section 19.2)
• XDM configuration files (Section 19.3)
• XDM log files(Section 19.4)
• XDM server startup and shutdown (Section 19.5)
• Configuring the XDM server(Section 19.6)
• Configuring other X displays (Section 19.7)
19.1 Key Concepts
The X Display Manager (XDM) is an X client that manages the login process of
a user’s X window session. XDM is responsible for displaying a login screen on a
display specified by an X server, establishing an X window session, and running
scripts that start other X clients. When the user logs out of the X session, XDM
is responsible for closing all connections and resetting the terminal for the next
user session.
An earlier version of XDM had limitations that were resolved with the
introduction of the XDM Control Protocol (XDMCP). Before XDMCP, XDM
used the XSERVERS file to keep track of the X terminals for which it managed
the login process. At startup, XDM initialized all X terminals listed in the
XSERVERS file. If the X terminal was turned off and then on again, XDM had
no way of knowing that a new login process should be initiated at the X terminal.
Configuring XDMCP-Compatible X Displays 19–1