GUI Applications - Displaying on a Linux Box

Introduction

There may be situations where you may log into a department unix server from a Linux or Solaris machine using SSH. When you try to run a GUI application such as Matlab in the logged on terminal it may not be displayed. You will get error messages saying that the DISPLAY is not set correctly. To be able to view graphics run on a remote machine on your local workstation certain display settings have to be made.

X - Windows

To display graphics on your local machine that is run on a remote machine you need X - Windows installed on your local machine. Generally most of the Linux and Solaris installations come with X-Windows. To check if you have X-Windows installed on your local machine make sure you login to your local machine in the desktop mode and not command mode and then open a terminal. Enter the following command:

'xhost'

If it returns with a 'command not found' message then X-Windows has not been installed in your machine. To know about X-windows and to install a free open source version of X-Windows go to http://www.xfree86.org/.

Make sure you have X -Windows installed on your local machine before going on to the next section.

Using SSH with X-forwarding

Once you have made sure that you have X-Windows in your local machine you can enable X-forwarding when using SSH.

Unfortunitaly not all SSH clients use the same command line flags so you will need to check your client for the specific flag. The two most common SSH clients are SSH a comercial product from the ssh corporation, and OpenSSH an open source alternative. Most linux instillations use OpenSSH (because it's free!) while most Sun instillations will use the comercial ssh client.

• SSH (commercial version)
  % ssh username@hostname +x
  
  
• OpenSSH (open source version)
  % ssh username@hostname -X

  (note that -X will enable and -x will disable so make sure it is uppercase)

To check that X-forwarding worked you can look at the DISPLAY enviornmental variable by %echo $DISPLAY. If the variable is not set then it did not work, check your client settings and check that X-forwarding is allowed on the machine which you are attempting to export from. If the variable is set correctly it should look something like hostname:10.0.

Since SSH connections to interactive.cs.tamu.edu are not blocked by the firewall you may use X-forwarding to your home machine without the use of VPN.