[torqueusers] X forwarding in interactive session

Daniel Challen daniel.challen at ocsl.co.uk
Wed May 28 10:15:29 MDT 2008

> I think the best course of action at this point is to configure the
> nodes to run ssh.
This is what I do everywhere. It's fairly simple on modern Unix-likes,
though you might want to do a bit of configuration so that your users do
not have to acknowledge server keys or authenticate themselves. Note
that using ssh does not compel you to run X11-over-SSH, you can still
have X11 run 'directly' over TCP.

> I have discussed this issue with the developer of our cluster software
> and he said that although this is possible he would not recommend it
> as the applications would run very slow. Is that consistent with the
> experience of others?
It depends what he means. If he is saying interactive GUI programs will
run slower when X11 is being tunnelled over SSH (over TCP), as opposed
to running 'directly' over TCP, there is some truth to that in the case
of graphically-intensive software. However, consider the fact that for
graphically-intensive 3D display, running over the network (whether
through SSH or direct) will be some orders of magnitude slower than
running every locally on your desktop anyway (memory, cpu and other
resource limits not withstanding).

If however he is saying parallel MPI-based software will run slower
because it's having to talk over SSH, he's much mistaken: SSH will only
be used for the initial set-up of the MPI group/universe (and if you use
the "tm" method to boot MPI, not even then) *not* for the

Hope that helps,
- Dan

I apologise if I've missed detail (MPI-or-not) from previous postings,
I've only just joined the list.

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