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Project: Linux  Articles
Guide to X-terminal setup
By Mayank Sarup <mayank@freeos.com>
Posted: ( 2000-10-25 08:03:09 EST by )
X-Terminals are a great way to revive your old machine or make your
diskless workstation that much more productive. StarOffice 5.2 may not run
on your 486, but you can run it off another machine and export the display
to your monitor.
The dusty old machine lying in the corner can be revived with Linux. But
when it comes to more memory hungry apps like Netscape and StarOffice then
you're at a loss. If however, you have a Linux machine on your network
with bigger hardware then you're in luck. Make that the X client and
designate the low end machine as the X server. The X-terminal concept is essentially like telneting into a machine and
then running some application there. All the working is done on the
machine that you are connecting to but the display is shown on your
machine. That just gives you access to console mode text applications,
whereas an X-Terminal setup will give you access to the entire range of
GUI applications. All applications will be run on the server but the
display will be exported to your computer. The machine that you setup as
the X terminal just serves as a display. This setup works very well with
diskless workstations and older computers. First a little theory for you. The X server is the software that handles
all the interactions between the GUI and your hardware. Windows equivalent
would be the graphics card driver. But X is a lot more than than. Here it
becomes a server that your clients connect to. Clients would be the
various GUI applications like GNOME, KDE etc communicating through network
protocols. This architecture allows a lot of flexibility. The clients can
be run on any machine but the display can be routed to another machine. For remote logins via X you need to enable xdm on the server. Xdm is the X
Display Manager which manages the login and authentication of users. Think
of it as the old text login screen with a nicer GUI layout. Good feature
is that not only does it authenticate users locally, it also provides a
login screen to any client that will connect to it. Find the xdm-config file. This should be in /usr/X11R6/lib/X11/xdm
(SuSE) or in /etc/X11/xdm (Red Hat, Mandrake). Open xdm-config. At the bottom of the file is look for a line that says DisplayManager.requestPort: 0 This line needs to be commented out ( Put a '#' in front of it ) if you
want to allow external X clients to be able to connect to the server. Edit the Xaccess file. Uncomment out the line with a '*' if it exists. If
not then add a line at the top which contains only a '*'. This will allow
hosts to connect directly to the server. There are several ways in which a client may connect to the server. 1. By directly specifying the host to connect to ( Direct query ). 2. Broadcast a request over the network which is taken up by the first
server to respond. 3. Make a indirect query where the client connects to a specific server
which in turn provides it with a list of servers that offer X logins. The
client selects the server to connect to from the list and then connects to
that server. Direct queries are fine over a small network. Next edit the Xservers file. There should be a line that looks like :0 local /usr/X11R6/bin/X :0 vt07. (SuSE) :0 local /usr/X11R6/bin/X (Red Hat) This line defines the virtual terminal that xdm will start on by default.
Comment this line out if you need the services of xdm but do not want it
to take up a terminal at startup. That's it. If xdm is running then restart it with killall -HUP xdm. Now for the client. The first thing to do is to setup the local X server.
Make sure that your video card is supported by and able to run X. Use
xf86config or the X setup tool that your distribution provides to set it
up. Red Hat has Xconfigurator and SuSE has Sax. After X is setup, all that
a client will need to run X -query xserver. e.g. - X -query foobar or X -query 192.168.0.12 What's given above is a direct query where I have specified the server
that I want to connect to. For broadcast queries use: X -broadcast The first server running xdm that responds will be the one you connect to. For indirect queries: X -indirect foobar On connecting to foobar, it will provide me with a list of willing hosts
on the network. Select the one you want to connect to and login there. Replace xserver with the hostname or IP address of the server that you
will be connecting to. You will be prompted with a login box. Just login
to the server with a login/password pair that is valid on the server and
you will be given access. Now you can run any applications that you want
on the server. Only the display will be exported to you. If everything is working then you might want to ensure that xdm is started
on the server at every boot. In most distributions you can just modify
/etc/inittab to start xdm at boot. Open /etc/inittab and go down till you
see a line like the one below id:2:initdefault: Change the '2' entry here to the runlevel where xdm will be started. This
would be 5 in the case of Red Hat and 3 for SuSE. As an alternative you can just start xdm from your startup scripts. If you
are using an alternative config file or your file is in some location
other than the default then you might want to use the parameter -config to
point xdm to your file. xdm -config /etc/xdm.config If the xdm screen looks a little plain, then you can instead choose to run
kdm. No other configuration is required. You should however take a look at
kdmrc. This will be in /opt/kde/share/config for SuSE and in
/usr/share/config/ for Red Hat. You can customize fonts, background
wallpaper and a host of other settings. The defaults should work fine. I haven't tried gdm but I expect it to be a drop in replacement for
xdm. If someone out there has tried it then please tell me.
Quick X-Terminal
If you just want to run a few applications off the server then you can
still do that and with a minimum of effort. Start X and open xterm or rxvt or your favourite terminal emulator for
X. In the terminal type the following. xhost +192.168.0.12 This will add the above address to the access control list. This will be
the IP or hostname of the machine on which you will be running the
application. This is needed to allow that machine to communicate with your
X server. You can also type 'xhost +' to disable all access control and
allow anyone to connect to your X server. Now telnet into the machine you specified above. telnet 192.168.0.12 Type the following on it. export DISPLAY=192.168.0.13:0 This will set the environment variable DISPLAY to point to your
machine. Replace this with your own IP address. The ':0' part is the
screen that any client application should connect to. You only need to
specify something else here if you're running multiple X sessions on your
machine. Just start the application. I've selected a suitably hoggy application. netscape This will start Netscape on the machine that you are connected to but
display everything on your monitor. Do not close the terminal that you
used to connect to that machine or you will break the connection and shut
down all the applications that you're running off the other machine.
Other articles by Mayank Sarup
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