[slurm-users] Srun not setting DISPLAY with --x11 for one account

[Simon Andrews]

I have a weird problem which I can't get to the bottom of.

We have a cluster which allows users to start interactive sessions which forward any X11 sessions they generated on the head node.  This generally works fine, but on the account of one user it doesn't work.  The X11 connection to the head node is fine, but it won't transfer to the compute node.

The symptoms are shown below:

A good user gets this:

[good at headnode ~]$ xauth list
headnode.babraham.ac.uk/unix:12  MIT-MAGIC-COOKIE-1  f04a2bf9a921a3357e44373655add14a

[good at headnode ~]$ echo $DISPLAY
localhost:12.0

[good at headnode ~]$ srun --pty -p interactive --x11  --preserve-env /bin/bash

[good at compute ~]$ xauth list
headnode.babraham.ac.uk/unix:12  MIT-MAGIC-COOKIE-1  f04a2bf9a921a3357e44373655add14a
compute/unix:25  MIT-MAGIC-COOKIE-1  f04a2bf9a921a3357e44373655add14a

[good at compute ~]$ echo $DISPLAY
localhost:25.0

So the cookie is copied from the head node and forwarded and the DISPLAY variable is updated.

The bad user gets this:

[bad at headnode ~]$ xauth list
headnode.babraham.ac.uk/unix:10  MIT-MAGIC-COOKIE-1  c39a493a37132d308b37469d363d8692

[bad at headnode ~]$ echo $DISPLAY
localhost:10.0

[bad at headnode ~]$ srun --pty -p interactive --x11  --preserve-env /bin/bash

[bad at compute ~]$ xauth list
headnode.babraham.ac.uk/unix:10  MIT-MAGIC-COOKIE-1  c39a493a37132d308b37469d363d8692

[bad at compute ~]$ echo $DISPLAY
localhost:10.0

So the cookie isn't copied and the DISPLAY isn't updated.  I can't see any errors in the logs and I can't see anything different about this account.

If I do a straight forward ssh -Y from the head node to a compute node from the bad account then that works fine - it's only whatever is specific about the way that srun forwards X which fails.

Any ideas or suggestions for debugging would be appreciated as I'm running out of things to try!

Simon.
The Babraham Institute, Babraham Research Campus, Cambridge CB22 3AT Registered Charity No. 1053902.
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