[MLUG] Remote X for Bengal HOWTO

[Mark Rages <EMAIL:PROTECTED>]

On Tue, Sep 07, 2004 at 12:34:50PM -0500, Christian M. Cepel wrote:
> I just wasted a night trying to figure out how to run an X app my wife 
> has used before, which exists in bengal, and has successfully run for 
> her CECS365 (I think) class using the SGIs in ebw.

OK, I figured a way.  I wrote two scripts to use:

First, log into Bengal.  This script will install an xterm for you.  I 
just copied the one from my Fedora box:

#!/bin/sh
echo "This script downloads and installs an xterm for Bengal use"

BINDIR=~/bin
XTERM=xterm

mkdir -p $BINDIR
cd $BINDIR
wget http://mlug.missouri.edu/~markrages/xterm
chmod +x xterm

grep $BINDIR ~/.tcshrc >/dev/null || \
( echo "setenv PATH \${PATH}:$BINDIR" >> ~/.tcshrc && \
  \
  echo "Run this command and xterm installation will be complete:" && \
  echo "source ~/.tcshrc ; rehash" )

echo "Done"

# END SCRIPT

Now, log out.

Run this script to open an xterm on Bengal:

#!/bin/sh
BENGAL_UID=abc123

OFFSET=$(( 10 + `date +%S` ))

echo "Allowing connections from localhost."
xhost +127.0.0.1

exec ssh -R$(( 6000 + $OFFSET )):127.0.0.1:6000 
EMAIL:PROTECTED "xterm -display 127.0.0.1:$OFFSET"

echo "Disallowing connections from localhost."
xhost -127.0.0.1

# END SCRIPT

Notice the Bengal userid is hardcoded in the second line.  Adjust 
appropriately.

Now this second script has huge limitations:

1) the port on Bengal may be in use.  I semi-randomly choose a screen 
between 10 and 70 based on the seconds of the wall clock.

2) The script opens your local X session to any user on the local host.  
Any user on the local computer could look at your window or read your 
keystrokes.  This is no better security than a Windows user would have. 
I messed around with xauth to try to do this properly, but what a mess!

3) The script closes your local X session after it's done.  Maybe you 
*wanted* it to be open.

4) The script should really send off an email to Bengal support each
time it runs, asking them to fix X tunneling properly.  I mean, making
users' lives difficult often results in decreased security, whether it
is forcing password changes (which results in
sticky-notes-on-the-monitor) or in unskilled hacks like this script.

Regards,
Mark
EMAIL:PROTECTED
-- 
You think that it is a secret, but it never has been one.
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