Running Graphical Programs Over SSH #

Although SSH connections are done through a command line interface, it is actually possible to run graphical applications over SSH using X-forwarding.

This trick can be useful for CS314 because some of our assignments use a GUI window. If you want to test one of these graphical programs on the lab machines, you’ll need to use X-forwarding. If you do not have X-forwarding enabled, you’ll get an exception which looks similar to this:

Exception in thread "main" java.awt.HeadlessException:
No X11 DISPLAY variable was set, but this program performed an operation which requires it.
	at java.desktop/java.awt.GraphicsEnvironment.checkHeadless(GraphicsEnvironment.java:208)
	at java.desktop/java.awt.Window.<init>(Window.java:548)
	at java.desktop/java.awt.Frame.<init>(Frame.java:423)
	at java.desktop/javax.swing.JFrame.<init>(JFrame.java:224)
	at DrawingPanel.<init>(DrawingPanel.java:87)
	at Recursive.drawCarpet(Recursive.java:188)
	at RecursiveTester.doCarpetTest(RecursiveTester.java:33)
	at RecursiveTester.main(RecursiveTester.java:27)

Windows

One-Time Setup

Windows does not have a built-in X-Windows server so we’ll need to install one. Xming is a free and popular choice. You can download the installer here.

Open a command prompt and type the following commands:

mkdir \dev
echo x > \dev\tty

Every-Time Setup

Make sure that Xming is running (it will be in the system tray when running) and run the following three commands in the command prompt. When connecting to the lab machine, you’ll need to add an extra argument to the ssh command:

set DISPLAY=localhost:0
echo x > \dev\tty
ssh -Y CS_USER@CS_MACHINE.cs.utexas.edu

macOS

One-Time Setup

macOS does not have a built-in X-Windows server so we’ll need to install one. XQuartz is free, open source and a popular option for macOS. You can download the installer here.

Next, we need to tell ssh where to find xauth, another program which will allow us to set up a secure X-Windows connection. All this means for you is you need to add the following line in the ~/.ssh/config file on your local machine:

XAuthLocation /opt/X11/bin/xauth

You should now be ready to get connected!

Every-Time Setup

Once that is complete, you need to add an extra argument to the ssh command you use to connect to the lab machine:

ssh -X CS_USER@CS_MACHINE.cs.utexas.edu

Linux

One-Time Setup

None! Linux is by far the easiest platform for using X-Forwarding because it has XWindows built in!

Every-Time Setup

All you need to do is add an extra argument to the ssh command you use to connect to the lab machine:

ssh -X CS_USER@CS_MACHINE.cs.utexas.edu

To test if enabling X-forwarding worked, try running this command on the lab machine over SSH:

xcowsay "Hello, World\!"

If you see the message on your screen, it worked! You should now be able to run your graphical Java programs.