[slurm-users] Running vnc after srun fails but works after a direct ssh

[Jeremy Fix]

Hello !

I'm facing a weird issue. With one user, call it gpupro_user , if I log
with ssh on a compute node, I can run a vncserver (see command [1] 
below) succesfully (in my case, a tigervnc server). However, if I
allocate the exact same node through a srun (see command [2] below),
running vnc server fails with the error given at the end of this message.

And finally, if I do the exact same srun, having the exact same computer
node, from another login (my own login actually), and then start
vncserver with the exact same command, it works.

So, do you think there is anything in the way we configured the user
gpupro_user, or maybe declared it in sacctmgr or somewhere that could
explain why running vncserver from within the srun session fails ?

Thank you for your help.

Have a nice day ;

Jeremy.

[1] vncserver -SecurityTypes None -depth 32 -geometry 1680x1050

[2]  srun --nodelist=tx01 -N 1 -p gpue60 -t 0:30:00 --pty bash

------- VNC error ----------------------------------------

Please be aware that you are exposing your VNC server to all users on the
local machine. These users can access your server without authentication!

New 'tx01:1 (gpuaut_2)' desktop at :1 on machine tx01

Starting applications specified in /etc/X11/Xvnc-session
Log file is /usr/users/gpuaut/gpuaut_2/.vnc/tx01:1.log

Use xtigervncviewer -SecurityTypes None :1 to connect to the VNC server.


vncserver: Failed command '/etc/X11/Xvnc-session': 256!

=================== tail -15 /usr/users/gpuaut/gpuaut_2/.vnc/tx01:1.log
===================
Killing Xtigervnc process ID 31975... which seems to be deadlocked.
Using SIGKILL!

Xvnc TigerVNC 1.7.0 - built Dec  5 2017 09:25:01
Copyright (C) 1999-2016 TigerVNC Team and many others (see README.txt)
See http://www.tigervnc.org for information on TigerVNC.
Underlying X server release 11905000, The X.Org Foundation


Sat May 15 13:57:35 2021
 vncext:      VNC extension running!
 vncext:      Listening for VNC connections on local interface(s), port 5901
 vncext:      created VNC server for screen 0
XIO:  fatal IO error 11 (Resource temporarily unavailable) on X server ":1"
      after 175 requests (175 known processed) with 0 events remaining.
Killing Xtigervnc process ID 7169... which seems to be deadlocked. Using
SIGKILL!

===========================================================================================

Starting applications specified in /etc/X11/Xvnc-session has failed.
Maybe try something simple first, e.g.,
    tigervncserver -xstartup /usr/bin/xterm
------- VNC error ----------------------------------------