ubuntu20 desktop changes

As proof-of-concept, we can now run Ubuntu 20.04 desktop on our cluster. We used the m3t000 machine for this, and the list of the changes that we need to do are below (reason for change in brackets):

• 1. Remove python-is-python3
• 2. Set default python to python2: sudo update-alternatives --install /usr/bin/python python /usr/bin/python2 1 (to get get-xorg.py to work on Ubuntu 20.04, only works with python2)
• 3. Add source /etc/profile.d/modulecmd.sh to the top of the desktop.slurm or sbatch_vis_session (to get module to work in the slurm script)
• 4. Edit /etc/X11/Xwrapper.config and change allowed_user variable to allowed_user=anybody (this is to get xinit to work, by default it is locked to console only so can't start xterm via ssh without changing this config)
• 5. Run dpkg-reconfigure xserver-xorg-legacy to make sure /etc/X11/Xwrapper.config doesn't get overridden during update (see the conf file for more detail)
• 6. Update /usr/local/desktop/desktop_start_arg to replace hard-coded lspci with which lspci (this is a legacy script from Paul Mac, all the GUI apps use this script to start - this is now done, changes merged)
• 7. Install python-tk package (this is to get the Desktop Walltime script to work)
• 8. Add the below code to /etc/bash.bashrc (this is to get module command to work from terminal on the desktop)

if [ -f /etc/profile.d/modulecmd.sh ]; then
 . /etc/profile.d/modulecmd.sh
fi

All except no. 6 needs to be put int ansible I am testing a couple of applications that aren't working (ChimeraX 0.91 seems to work on P4 but not T4, but ChimeraX 0.93 works on both) and if you want to play around, let me know. I tested this using Strudel Desktop, so I will still need to test this on Strudel 2.