Re: Problem with running X apps

[Harold L Hunt II <huntharo at msu dot edu>]

Kerry,

No, the encryption should not slow things down much.  You may also want 
to try the -C parameter to ssh, which causes network packets to be 
compressed.

However, have a look at your network hub before starting your ssh 
session and see how many collisions you are getting.  Lots of collisions 
on a network segment with less than 50 computers with active users at 
them is a sure sign of network misconfiguration.  At one of my jobs we 
had 20 computers and at night, when no one was using the computers, the 
network collisions light was nearly blinking solid.  All of this wasted 
bandwidth turned out to be due to Windows machines broadcasting to 
discover other Windows machines.  Some of the machines were also setup 
with the wrong gateway/netmask so they would broadcast and not receive 
any responses (these machines also could not get on the Internet, which 
the other employees thought was just a fluke)... so those machines would 
broadcast-flood the network.  Setting up a WINS server and making the 
Windows machines look to the WINS server first fixed the problem.  After 
that our collisions light never blinked and we got about 5 times higher 
throughput.

Another tale is that my 100 Base-T switch hooked into the MSU campuses 
10 Base-T network would occasionally give agonizingly slow performance 
between the Windows computer and the Linux computer when using XDMCP. 
During these times the network activity lights were not blinking anymore 
than usual, so it does not seem that someone was accessing my computers. 
 Also, I was using a switch, so access times between local computers 
should be unaffected by traffic on the 10 Base-T network.  Yet if I 
unplugged the 10 Base-T network from the 100 Base-T switch the 
performance problem went away.  So, you should try unplugging everything 
else from your hub or switch once you have started your ssh session and 
see if performance improves.

I hope some of that helps,

Harold

Kerry Sanders wrote:
> Thanks Thomas.  This is the same thing that Jim posted earlier.
>
> What I needed was the -X on the ssh command.  However, does the
> encryption really slow stuff down that much?  I is really slow running X
> apps like KDE, etc. over my 100 Base-T network.
>
>
> -----Original Message-----
> First, I would recommend against running XWin directly.  Use the
> provided 
> startxwin.bat batch file instead and then run the ssh command from an
> xterm.
>
> However, if you REALLY want to do it this way, you need to set the
> DISPLAY 
> variable FIRST, then launch XWin, then run ssh with X forwarding turned
> on:
>
> cygwin> export DISPLAY=locahostname:0
> cygwin> XWin <options> &
> cygwin> ssh -X -l remoteusername remotehostname
>
> Once logged into the remote host, you can start running your Xclients
> right 
> way.  No need to set the DISPLAY variable yourself (or run xhost).  Ssh
> will 
> have already taken care of all of that.  In fact, setting the DISPLAY 
> variable as you describe below CIRCUMVENTS THE SSH CONNECTION ENTIRELY
> and 
> sends your XWindows traffic unencrypted!
>
> By the way, if the file .Xauthority exists in your home directory on 
> localhostname, it might cause problems.  If you find you are getting
> errors 
> that refer to "MIT-MAGIC-COOKIE", then delete the .Xauthority file and
> try 
> again.