Very useful!
The following article teaches how to use xauth add
" if you try to switch to another user on the remote system and export the display again, you would get and error – “Error: Can’t open display:”.
# ssh -X root@remotehost # su - [username] # export DISPLAY=x.x.x.x:y.y # xclock
Error: Can't open display: x.x.x.x:y.y
"
