[TriLUG] Newbie Question

[Paul D. Boyle]

> Sorry for the ignorance of this question, but I am new to this whole linux
> thing.

> It is my understanding that in linux it is possible to run an application
> on one machine, which is displaying its output and receiving input form
> another machine.  Is this true, what is this 'technology' called, so I
> can find out how to do it? Please also confirm or deny that this applies
> to graphical applications.

In broad terms, the technology is called 'networking' (sorry, that
probably wasn't very helpful).  If you are talking about graphical
applications, then X11 is a "network transparent" graphical environment.
This is old (approximately 1980's) technology in the Unix world (you
have to wonder why the leaders in "innovation" never came up with it,
but I digress). ;-)

X11 is very easy to use.  On the computer in front of which you are
sitting you run an X server (this can be done in a variety of ways).
Then you remote login to the remote computer on which you want to run
graphical client software.  The login can be done with traditional (and
insecure tools) like telnet, rlogin, rsh, a more modern and preferred way
is to use Openssh with provides an encrypted connection.  After logging
in, you run your program remotely and the graphical results are displayed
through your local X server on your screen.

There are some details depending on how you login to your remote machine.
You must somehow specify to your X server that the remote host is
authorized to make connections to the server.  For using Openssh, you
need to configure both sshd and ssh to forward X11 traffic. So, in sshd
configuration file (on my system it lives in /etc/ssh/sshd_config)
have the following lines:

X11Forwarding yes
X11DisplayOffset 10

And in the /etc/ssh/ssh_config file (the config file for the ssh client)
have this line:
   ForwardX11 yes

If you have tcp wrappers installed and have built a tcp wrapped version of
sshd add this to your /etc/hosts.allow file:
sshd, sshdfwd-X11: ALL # or whatever level of restriction you care to impose
                       # on the access.

You will also have to configure the sshd daemon on the remote system
analogously.  Read the man pages for X (i.e. man X), startx, xdm, xinit,
ssh and sshd for further information, or search the web for X11 tutorials. 

Good Luck,

Paul

-- 
Paul D. Boyle			    |	boyle at laue.chem.ncsu.edu
Director, X-ray Structural Facility |	phone: (919) 515-7362
Department of Chemistry - Box 8204  |	FAX:   (919) 515-5079
North Carolina State University     | 
Raleigh, NC, 27695-8204
http://laue.chem.ncsu.edu/web/xray.welcome.html