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 (if using Windows) and save it on your hard disk.

Configure Xming

• 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.
• Keep clicking on Next button till you reach the Finish configuration page, then click on the Finish button.

Configure PuTTY

• Start PuTTY.
• In the PuTTY Configuration section, on the left panel, select Connection → SSH → X11
• On the right panel, click on the Enable X11 forwarding checkbox
• Set the X display location as :0.0
• Click on Session option on the left panel.
• Enter the hostname or IP address in the Host Name textbox
• 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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If you have any questions, please contact me at arulbOsutkNiqlzziyties@gNqmaizl.bkcom. You can also post questions in our Facebook group. Thank you.