If you get error messages like this Xlib: connection to ":0.0" refused by server
Xlib: No protocol specified
xhost: unable to open display ":0.0"
when running a program, you probably need to add the user to the X server access list.
You can add a user to the X server access list with # xhost +local:username
This allows "username" to connect to the local running X server.