[torqueusers] Displaying X apps from a job

Mike Renfro renfro at tntech.edu
Fri Feb 17 09:52:25 MST 2006

On Thu, Feb 16, 2006 at 03:02:45PM -0700, John Hanks wrote:

> A given connection looks like:
> PC <-> eth0:MASTERNODE:eth1 <-> NODE
> eth0 has a public IP, eth1 is the internal private
> ( network. With my existing configuration I can
> ssh from PC to MASTER then ssh from MASTER to NODE, start and X app and
> it displays on PC.

> What I can't do is:
> ssh from PC to MASTER, submit job with X app and have job display on PC
> So I know it's possible for something running on a NODE to display back
> to PC, it just doesn't work through submitted jobs.

There are possibly several things at work here:

1) Does MASTER actually route, NAT, or masquerade traffic from the
nodes out to the rest of the public network? Can node systems ping or
otherwise contact systems outside their private network? If no, then
no direct display forwarding can happen except with the two-hop
process you have working. In that case, the only reason things are
working at all is that NODE can reach MASTER directly, and can send X
traffic to it. MASTER can reach your PC directly, and knows that your
X traffic from NODE should go to PC via ssh.

2) If the answer to the above routing question is yes, then if you
'qsub -I' to a node, can you set your DISPLAY variable back to PC:0 or
PC:0.0 and get any X app (xlogo, xterm) to display? If you get a
"cannot open display" error at that point, then does your local PC
allow X connections from other systems? If all you've done in the past
is X over ssh, then it's possible that PC is set to only allow X
connections from localhost, which is more secure, and works fine with
X forwarding over ssh. 'xhost +' on NODE won't help at all, you'd need
to do that on PC (but maybe I misread, and you've already done that).

Mike Renfro  / R&D Engineer, Center for Manufacturing Research,
931 372-3601 / Tennessee Technological University -- renfro at tntech.edu

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