This is a beginners question, I know... but I have searched and I'm getting frustrated. I know my way around Lunux pretty well, but I have never had to deal with XServer.

Question 1:

I SSH from OSX into a UBUNTU 14.04 desktop machine as user alpha.

User alpha is also logged in locally on that desktop.

I want to run (via my terminal) an application that should show on the UBUNTU machine (so that its visible on the locally display of the locally logged in user).

Today I get this error when I do this from the OSX terminal:

15:21:20:157 AWT-EventQueue-0: Error
No X11 DISPLAY variable was set, but this program performed an operation     which requires it.
at java.awt.GraphicsEnvironment.checkHeadless(GraphicsEnvironment.java:207)
at java.awt.Window.<init>(Window.java:535)
at java.awt.Frame.<init>(Frame.java:420)

NOTE: When I do it from the local terminal (on UBUNTU) it works as it should, so theres nothing wrong with the program.

Question 2:

In case the UBUNTU machine was headless, how would I divert the windows to another machine, for example my Mac?

Thanks Peter

3 Answers 3


For your second question: add the -X (or -Y for a trusted connection) parameter when connecting with ssh and make sure you have X11 on your mac. Example:

ssh -X myuser@mylinux.machine

That would route your X11 windows to show on your local X server on your mac.

See: https://developer.apple.com/library/mac/documentation/Darwin/Reference/ManPages/man1/ssh.1.html

For the first question:


An X program needs two pieces of information in order to connect to an X display.

  • It needs the address of the display, which is typically :0 when you're logged in locally or :10, :11, etc. when you're logged in remotely (but the number can change depending on how many X connections are active). The address of the display is normally indicated in the DISPLAY environment variable.

  • It needs the password for the display. X display passwords are called magic cookies. Magic cookies are not specified directly: they are always stored in X authority files, which are a collection of records of the form “display :42 has cookie 123456”. The X authority file is normally indicated in the XAUTHORITY environment variable. If $XAUTHORITY is not set, programs use ~/.Xauthority.

Extracted from: https://unix.stackexchange.com/a/10126

Refer to that post for a great explanation.


Remotely, you would need to set the display to use by exporting the DISPLAY environmental variable.

eg. export DISPLAY=:0

For your second question, the easiest way would be to set up VNC server on ubuntu and use a VNC client to connect from your Mac.

How-to: http://www.howtoforge.com/how-to-install-vnc-server-on-ubuntu-14.04


1) I'm not sure, maybe try export DISPLAY=0?

2) To show the GUI on the machine you're using, run SSH with the -Y option.

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