This document describes the basic concepts behind using XDM
(the X Display Manager) to manage X terminals and X servers,
in order to provide 'thin-client' computing, using Linux.
X (or the 'X Window System') is the windowing and graphics environment
of choice for Unix systems. Its particular strength (and the key bit
that we are interested in for this document) is that it separates the
running applications (web browser, word processor, etc) from the actual
graphics screen and input devices (mouse, keyboard, etc) via a network
communications mechanism.
Essentially, this means that you can be running
an application on one machine, but have its input and output redirected
to another machine via a network. This is the key feature that makes
an X terminal possible.
This document should be treated as a 'getting started with XDM' document,
in that it describes the basic terms and concepts for using XDM and
X terminals, with simple examples that provide the minimum amount of
security.
The reader is advised to consult the list of resources provided at
the end of the document in order to proceed beyond these basic
facilities - in particular, the configuration of the 'authentication'
and security settings should be examined, as the examples given in
this document utilise the least secure modes of operation.
Please note - the majority of the information in this document was obtained from
systems running Debian 2.1, SuSE 6.4, Mandrake 7.0 and RedHat 6.0.
This document does not discuss the installation or
configuration of a network or X on Linux. Please refer to the
appropriate HOWTO documents from the Linux Documentation Project for
details (see Section 7).
This document also does not attempt to describe how to install and configure
Linux for operation as an X terminal. For this information, please refer
to the 'thin-client' HOWTO document, provided as part of the Linux Documentation
Project, or the Linux Terminal Server Project (see Section 7).
This document came about because I wanted to experiment with Linux
on a 486 PC as an X terminal to my main Linux box.
After reading the man pages, specifications and current howto documents
relating to XDM and X terminals, I ended up getting really confused
about where XDM was supposed to run and confusing XDM servers with
X servers and the like, and so after an evening or two of
experimentation, this document was born.
Once the basic terminology has been sorted out, the documentation
for XDM and self-documenting sample files make very good reading
- I just could not find a simple introduction to the basic concepts
anywhere to get me started. Hopefully this document could prove
to be a suitable introduction to someone in a similar position to
me.
Oh, and in case you are wondering, a 486dx2/66 with 16 Mb RAM
makes a fine X terminal!
Take our 
