9.3.2 X Clients
Programs that communicate with the X server are called X clients. Most of these programs will ask the X server to display windows on the screen.
You start an X client the same way you start any other Debian program. Simply type the name of the client on the command line. Try typing xterm into an existing xterm window, and a new xterm client will appear on the screen.
You may notice that the original xterm is now useless, because your shell is waiting for the second xterm to finish. To avoid this problem, you can run the X client in the backgroundby adding a & after the command name like this: xterm &. If you forget, you can place a running process in the background. First suspend the process with CTRL-z, and then place it in the background with the bg command.
If you use a program often, your window manager will generally provide a way to put that program on a convenient graphical menu.
9.3.3 Troubleshooting
Sometimes when you launch an X client from a graphical menu, you won’t be able to see any error messages if it fails. You can find any error messages in the file ~/.xsession-errors.
9.3.4 Leaving the X Environment
To leave X, you need to use a menu. Unfortunately for beginners, this is different for every window manager, and for most window managers, it can be configured in many ways. If there’s an obvious menu, look for an entry like “Exit” or “Close Window Manager.” If you don’t see a menu, try clicking each of the mouse buttons on the background of the screen. If all else fails, you can forcibly kill the X server by pressing CTRL-ALT-Backspace. Forcibly killing the server destroys any unsaved data in open applications.