[slurm-users] SLURM 20.11.0 no x11 forwarding.

[Luis R. Torres]

Hi Folks,

I'm currently running a small but powerful 10 node cluster where we require the scheduling of certain graphical apps.  Our SLURM version is 20.11.0, half our nodes are RHEL7 and the other half Ubuntu 18.04.

Our slurm config related to x11 is:

PrologFlags=x11

X11Parameters=home_xauthority

We get the following error when attempting to use forwarding using SLURM

srun --nodelist=node01 --x11 xeyes

X11 connection rejected because of wrong authentication.

Error: Can't open display: localhost:78.0

srun: error: node01: task 0: Exited with exit code 1

The steps we take are:

ssh -X user@login-node

[user@login-node]$ srun --nodelist=node01 --x11 xeyes

No user accounts are allowed to SSH directly into execution nodes, only a few special user accounts, however, those accounts have issues when using --x11 but have NO issues when connecting directly (and forwarding) to the execution nodes.

We went through this group to determine if anyone else has had similar issues resolved but I didn't find anything other than some recommendations.  Has someone actually resolved this particular (or very similar) issue?

Our sshd_config is as follows:

X11Forwarding yes

X11DisplayOffset 10

X11UseLocalhost no

Our cluster is configured with SlurmUser=slurm, not root.

Thanks,

--

----------------------------------------
Luis R. Torres

[Rodrigo Santibáñez]

Did you compile SLURM with x11 support?

[Luis R. Torres]

I believe that was the case, we compiled it with x11 support, however, further debugging suggests that there's an issue writing to the .Xauthority file when using forwarding through srun.

[Prentice Bisbal]

If you're getting an .Xauthority error, then X11 support was definitely
compiled into Slurm. The most common cause of .Xauthority issues is the
user's home directory hitting their quota limit. Could that be the case
here?

--
Prentice

[Tina Friedrich]

No idea if I replied this to this particular thread already (if I have
sorry for the duplicate).

I had issues getting X forwarding to work with SLURM at the start.
Worked via SSH; no authentication / xauth problems when doing via SLURM.

Turned out to be caused by the nodes having their hostname set to their
'long' hostname (i.e. including domain) - I think that might be Red Hat
default? I 'fixed' it by changing things so all things cluster (i.e. all
things that have SLURM installed) have their hostname set to the short
hostname.

Tina

--
Tina Friedrich, Advanced Research Computing Snr HPC Systems Administrator

Research Computing and Support Services
IT Services, University of Oxford
http://www.arc.ox.ac.uk http://www.it.ox.ac.uk