xdm for X terminals

To use an X terminal with your host, xdm must first be running on the host machine. The host listens for inbound connections from the X terminals using XDMCP, the xdm Control Protocol (the default port for xdmcp is 177). When a request is received, xdm responds with the same graphical login screen that’s used on the local system. The difference is that the X server is implemented in the X terminal hardware, not in the XFree86 software on the xdm host, and all of the graphics information is transmitted over the network.

You can configure access to your system’s xdm daemon in the /etc/X11/xdm/Xaccess file. This file is a simple list of hosts that are to be restricted or enabled. To enable a host, simply enter its name. To restrict a host, enter its name with an exclamation point (!) before it. The * wildcard is also allowed to handle groups of devices.

The following example allows access to all X terminals on the local domain but prohibits access from xterm1 on an outside domain:

*.example.com
!xterm1.anotherexample.com

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