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<p class="MsoNormal">I have a weird problem which I can’t get to the bottom of. <o:p>
</o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">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.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">The symptoms are shown below:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">A good user gets this:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">[good@headnode ~]$ xauth list<o:p></o:p></p>
<p class="MsoNormal">headnode.babraham.ac.uk/unix:12 MIT-MAGIC-COOKIE-1 f04a2bf9a921a3357e44373655add14a<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">[good@headnode ~]$ echo $DISPLAY<o:p></o:p></p>
<p class="MsoNormal">localhost:12.0<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">[good@headnode ~]$ srun --pty -p interactive --x11 --preserve-env /bin/bash<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">[good@compute ~]$ xauth list<o:p></o:p></p>
<p class="MsoNormal">headnode.babraham.ac.uk/unix:12 MIT-MAGIC-COOKIE-1 f04a2bf9a921a3357e44373655add14a<o:p></o:p></p>
<p class="MsoNormal">compute/unix:25 MIT-MAGIC-COOKIE-1 f04a2bf9a921a3357e44373655add14a<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">[good@compute ~]$ echo $DISPLAY<o:p></o:p></p>
<p class="MsoNormal">localhost:25.0<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">So the cookie is copied from the head node and forwarded and the DISPLAY variable is updated.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">The bad user gets this:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">[bad@headnode ~]$ xauth list<o:p></o:p></p>
<p class="MsoNormal">headnode.babraham.ac.uk/unix:10 MIT-MAGIC-COOKIE-1 c39a493a37132d308b37469d363d8692<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">[bad@headnode ~]$ echo $DISPLAY<o:p></o:p></p>
<p class="MsoNormal">localhost:10.0<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">[bad@headnode ~]$ srun --pty -p interactive --x11 --preserve-env /bin/bash<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">[bad@compute ~]$ xauth list<o:p></o:p></p>
<p class="MsoNormal">headnode.babraham.ac.uk/unix:10 MIT-MAGIC-COOKIE-1 c39a493a37132d308b37469d363d8692<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">[bad@compute ~]$ echo $DISPLAY<o:p></o:p></p>
<p class="MsoNormal">localhost:10.0<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">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.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">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.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Any ideas or suggestions for debugging would be appreciated as I’m running out of things to try!<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Simon.<o:p></o:p></p>
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