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A number of programs with graphical user interfaces (e.g., R, MATLAB) use the X11 system which lets the program run on an O2 computer, but show the graphics on your desktop. Even to activate the graphics devices and plot to files, an X11 session must be enabled. To do this, you need to have an X11 server running on your desktop, your SSH connection needs to have X11 forwarding enabled, and you will need to authenticate (i.e., enter your password or use SSH keys) when submitting a Slurm job.
If you have SSH X11 forwarding enabled in your SSH client and are running an X11 server on your local system, you can run X11 jobs on the O2 compute nodes. As of the July 7, 2020 upgrade, batch jobs now have X11 forwarding enabled by default without any sbatch flag required (provided you submitted a job after having logged in with the corresponding ssh flag, see below). However, in order to utilize X11 forwarding in an interactive session, it is still necessary to specify the --x11 flag, like
srun --pty -p interactive -t 0-12:00 --x11 /bin/bashNote: Submitting Slurm jobs with the --x11 flag requires authentication. You can manually type your password or configure SSH keys prior to submitting the X11 job.
X11 Terminology
X11 client
The application being displayed (xterm, XEmacs, Mozilla, etc.) You would run this, e.g., on O2
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