How to handle X11 Forwarding using SSH

If you need to use X applications/GUI over a remote SSH connection via PuTTY, this tutorial is for you.

What you need

  • Xming : an X-Server that starts on top of your desktop.
    Download Xming and install it.
  • PuTTY : an SSH client.
    Download PuTTY and save it on your hard disk.

Configure Xming

  1. Click on the Start button in Windows XP, select Xming → XLaunch
    At the Display settings dialog box, select Multiple windows and set the Display number as 0. Click on Next.
  2. Keep clicking on Next button till you reach the Finish configuration page, then click on the Finish button.

Configure PuTTY

  1. Start PuTTY.
  2. In the PuTTY Configuration section, on the left panel, select Connection → SSH → X11
  3. On the right panel, click on the Enable X11 forwarding checkbox
  4. Set the X display location as :0.0
  5. Click on Session option on the left panel.
  6. Enter the hostname or IP address in the Host Name textbox
  7. Save the session.

Running the X applications from PuTTY

  • Double-click on your PuTTY session and login. After you login, a file named .Xauthority will be created.
  • Check if the DISPLAY variable has been set. 
    echo $DISPLAY
    You should see a meaningful value for $DISPLAY
  • Start any X application, say xterm. 
    xterm
    The xterm window should open successfully.

Running X apps as root

This requires a little tweak. Suppose your regular user home directory is /var/home/arul and the root user home directory is /root

  • If you were able to login as a normal user earlier, a file called .Xauthority would be created in the home directory. Chmod the .Xauthority to 555. 
    chmod 555 ~/.Xauthority
  • Login as root from your regular user account. 
    su - root
  • Copy the .Xauthority from the regular user's home directory to root user's home directory. 
    cp /var/home/arul/.Xauthority /root
  • Now try to open any X apps like xterm or emacs. It should work.

Troubleshooting

If you're not able to open any X apps from the session, you may need to enable X11 SSH Forwarding in the /etc/ssh/ssh_config file

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