This is a bit complicated and highly specific case so I will try with a high level description and if necessary delve deeper. My purpose is to run ROS (Robot Operating System) on a Digital Ocean node so that I don't have to set it up on my Mac (anyway, it won't run properly on a Mac.)
I'm running Ubuntu 18.04 on the Digital Ocean node. There I am running xfce4 and tightvncserver.
On my mac, I am creating the tunnel to the above server with this command:
ssh -L 5901:127.0.0.1:5901 -C -N -l <myname> <myip>
On my Mac I then use
vncviewer to connect to the Digital Ocean Server, and that seems to work fine.
When I launch the most basic ROS simulator, which normally would open a graphical window if I was running on a native ubuntu box I get this error:
Any thoughts on what is broken and how to fix it?