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Subject: Re: [OMPI users] mpirun, paths and xterm again
From: Tim Prins (tprins_at_[hidden])
Date: 2008-02-05 13:03:47


jody wrote:
> Hi Tim
>> Your desktop is plankton, and you want
>> to run a job on both plankton and nano, and have xterms show up on nano.
> Not on nano, but on plankton, but ithink this was just a typo :)

>> It looks like you are already doing this, but to make sure, the way I
>> would use xhost is:
>> plankton$ xhost +nano_00
>> plankton$ mpirun -np 4 --hostfile testhosts -x DISPLAY=plankton:0.0
>> xterm -hold -e ../MPITest
> This gives me 2 lines of
> xterm Xt error: Can't open display: plankton:0.0
>> Can you try running:
>> plankton$ mpirun -np 1 -host nano_00 -x DISPLAY=plankton:0.0 printenv
> This yields
> DISPLAY=plankton:0.0
>> just to make sure the environment variable is being properly set.
>> You might also try:
>> in terminal 1:
>> plankton$ xhost +nano_00
>> in terminal 2:
>> plankton$ ssh -x nano_00
>> nano_00$ export DISPLAY="plankton:0.0"
>> nano_00$ xterm
> This experiment also gives
> xterm Xt error: Can't open display: plankton:0.0
>> This will ssh into nano, disabling ssh X forwarding, and try to launch
>> an xterm. If this does not work, then something is wrong with your x
>> setup. If it does work, it should work with Open MPI as well.
> So i guess something is wrong with my X setup.
> I wonder what it could be ...

So this is an X issue, not an Open MPI issue then. I do not know enough
about X setup to help here...

> Doing the same with X11 forwarding works perfectly.
> But why is X11 forwarding bad? Or differently asked,
> does Opem MPI make the ssh connection in such a way
> that X11 forwarding is disabled?

What Open MPI does is it uses ssh to launch a daemon on a remote node,
then it disconnects the ssh session. This is done to prevent running out
of resources at scale. We then send a message to the daemon to launch
the client application. So we are not doing anything to prevent ssh X11
forwarding, it is just that by the time the application launched the ssh
sessions are no longer around.

There is a way to force the ssh sessions to stay open. However doing so
will result in a bunch of excess debug output. If you add
"--debug-daemons" to the mpirun command line, the ssh connections should
stay open.

Hope this helps,