[H-GEN] xterminal doc by popular demand

[Robert Brockway]

Hi. A number of people have requested by document explaining how to setup
a Linux box as an Xterminal off another box.  As I can't remember all the
names, and suspecting others may find it slightly interresting, I am
sending it to general.

You can find it attached.
Cheers,
	-Robert

--Robert Brockway B.Sc.  Email: robert at zen.humbug.org.au, robert at icc.net.au
				r.brockway at uq.edu.au
                         WWW:   http://www.humbug.org.au/~robert
                         President of HUMBUG (http://www.humbug.org.au)
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		Setting up a Linux box to act as an X terminal
		==============================================

A discussion of setting up a Linux box as a Xterminal, by Robert Brockway.
(c) Copyright Robert Brockway 1997.  Permission is given to distribute
this document in electronic or other format in an unaltered state.

Version 1.2

Last modified 5/3/98.

This short document discusses how to setup a Linux machine as an Xterminal
which will allow logins to another machine running Unix.

In this discussion I will refer to the following machines:

xavier (192.168.105.241): An X terminal which will allow logins to randal.
randal (192.168.105.242): The remote host which will sending xdm to xavier.
Users will actually be logging in to randal.

See the Glossary at the end for a discussion of terms.

				Setup Procedure
				---------------

To setup a Linux box as an X terminal the following procedures should be
followed.  This procedure can be divided in to several parts:

1) Setting up the X terminal xavier.

First off ensure the Linux machine is up and running.  Very little needs
to be running on the X terminal.  As long as the user can establish a
network connection and ping remote hosts, the X terminal is ready to go.

It is probably preferable to remove any unneccessary services from
/etc/inetd on the X terminal, as they only pose an unneccessary security
risk.
 
To make the X server start in runlevel 5 and query the remote host
rover for a login, add the following line to /etc/inittab:

        x1:5:respawn:/usr/X11R6/bin/X -query randal

Comment out or remove any other lines that refer to starting X or xdm in
runlevel 5.

The 'x1' at the start of the line is a unique marker in /etc/inittab, so
if multiple X lines are desired, use x1,x2,etc.

This command will cause an X server to start and to query the machine
'randal' to start an xdm session on the console of xavier.

2) Setting up the remote host randal to send an xdm session to xavier.

To make randal send an xdm session to xavier ensure there is an
uncommented line in /etc/inittab that looks like this:

        x1:5:respawn:/usr/bin/X11/xdm -nodaemon

In /usr/X11/lib/X11/xdm/Xservers add the following:

        xavier:0 foreign

This will be in addition to the line that starts the X server locally on
randal if there is a need for a local X server.

Then change both machines to runlevel 5.  Once it is clear that this is
working, the default runlevel can be changed to runlevel 5 on both
machines. To do this, find a line at the beginning on /etc/inittab
on both machines that looks like this:

        id:3:initdefault:

Change it to this:

        id:5:initdefault:

Everything should be working now! (with luck ;-)

3) Possible access problem.

Depending on how the X server is setup initially, the following may be  
necessary.  I have never needed to set this up, but it is mentioned
asa possible 'gotcha'.

If the Xserver initally refuses access to xdm, create the file
/etc/X0.hosts on xavier, containing the IP or hostname, one per line, of
hosts that will be allowed to make contact with the X server initially.
For xavier the following might be an example /etc/X0.hosts file:

        192.168.105.242

This is the IP of randal.  It is more secure to use the IP as a hostname
is only as secure as the dns system (unless you use a /etc/hosts file, which
is generally not a good idea for reasons outside the scope of this document).

				Glossary
				--------

Before enterning into a discussion of X terminals, the reader must
understand the terminology in use.

Client-Server Model:

The location of the X server on the X terminal often causes confusion to
those new to the concepts of the X protocol.  This confusion arrises as
many people are more used to the concept of a server being on a remote
machine while a client is on a local machine.  This is a false assumption
in regards to the client-server computing model.  There is, in general, no
need for a client or server to be in any particular part of the network.
The easiest way to remember whether a particular program is a client or a
server is to remember that users interact with client applications while
clients interact with servers, and in general it is the servers that
interact with the rest of the system.

xdm: The X Display Manager.  Used to manage logins through the X Window
System.

X client:  This is an application program running locally or remotely on
the network which can be displayed on any host running an X server
(subject to permissions).
 
X terminal: A machine with (hopefully) fast graphical capabilities that
has the actual display the user will sit at attached to it.  This document
discusses setting up a Linux box to act as an X terminal.  This machine
has the X server running on it.

X server: This binary, running on the X terminal, is respnsible for
managing the physical display that the user sees.  It handles details
of the physical hardware, and is also network aware, allowing applications
that are running on another host on the network to be displayed on the
X terminal.