OS X Mountain Lion Bible

Using X11

Unix is a text-based operating system, but there is a graphical environment that can run in it. That GUI, called X Windowing System (or X11 for short), is provided with OS X in the Utilities folder: Just double-click the X11 application to open the X1 window in its Terminal view, called Xterm. There, you can type the name of the X11 application you want to run using the standard pathnames and press Return to run the application, or you can run an application by choosing it from the Applications menu. (Choose Applications⇒Customize to add applications to that list.)

X11 also loads automatically if you have downloaded an X11-based application onto your Mac and have launched that application. (You can put those applications in the Dock, create aliases to them, and otherwise manage their files like any OS X application.) The Gimp image editor is an example of such an X11 application.

When you run applications in X11, they appear onscreen in their own windows, as if they were OS X applications. Your only clues that you're running X11 is the set of X11 menus in the menu bar, as well as the usually slightly different visual style of X11 applications compared to OS X applications.

New Feature

X11 is not installed on your Mac with OS X Mountain Lion. Instead, the first time you use an X11 application in OS X Mountain Lion, an alert appears asking if you want to download the latest version.