[slurm-users] About x11 support

[Williams, Gareth (IM&T, Clayton)]

X11 comes up on this list now and then.  I'm often tempted to describe our site's approach and will do so now it case it help others (or someone wants to say why it is a terrible approach).

First some preamble:
 * we offer 'login' nodes with limits on what can be run as a highest-reliability option for managing batch jobs
 * we offer a set of 'interactive' nodes where there is more flexibility for running larger analysis, development and house-keeping tasks.
 * we offer a set of 'visualisation' nodes with gpus and setup for hardware accelerated graphics
 * we encourage use of (vnc) virtual desktop sessions, and/or ssh access

In both modes of access we ensure DISPLAY is set in a form that is network accessible within the cluster. ie _not_ localhost:NN
With ssh this is done with the sshd_config X11UseLocalHost=no option.

With DISPLAY set to a network accessible form and an xauth entry in the home directory, batch processes can access DISPLAY as long as the DISPLAY variable is passed into the job.

No plugin, no compiled in support in slurm. 

Note that DISPLAY is not in a form immediately accessible outside the cluster (not fqdn of the external interface) and we have various firewalls in place.

Gareth