How to display an X11 application on remote Ubuntu system

x11-listen.txt

Based on this page:

http://askubuntu.com/questions/72812/how-to-disable-nolisten

How to display an X11 application on remote Ubuntu system

display-host: ubuntu linux running X11 server
app-host: other linux with an X11 application

On the display-host:

     1. Edit /etc/lightdm/lightdm.conf and add the xserver-allow-tcp=true line below. If you don't have this file copy the contents below and create a new file.

        [SeatDefaults]
        xserver-allow-tcp=true
        greeter-session=unity-greeter
        user-session=ubuntu
        
        [XDMCPServer]
        enabled=true

     2. Restart X11 with sudo restart lightdm. 
     
     3. Check to see which port X11 is listening on with sudo lsof -i. We'll use this later to set the DISPLAY variable on the app-host.
     
     If the line looks like TCP *:x11 (LISTEN), your DISPLAY variable will end in :0.
     If the line looks like TCP *:x11-1 (LISTEN), your DISPLAY variable will end in :1.
     If the line looks like TCP *:x11-2 (LISTEN), your DISPLAY variable will end in :2.
     and so on.

     4. Login and start the X11 session if it isn't started automatically.

     5. Run `xhost +' (Note: You could be more specific here with your xhost argument. See the man page.)

On the app-host:

     1. If export DISPLAY=ip-address-of-display-host:0 or whatever colon-number suffix is appropriate based on your sudo lsof -i test above.

     2. Run the X11 application (eg: xclock &)

You should see the X11 application running on the app-host, but displayed on the display-host.