Running Linux, 5th Edition - Matthias Kalle Dalheimer [319]
X was originally developed by Project Athena at MIT, by MIT, Digital Equipment Corporation (DEC), and IBM. The version of X current as of the time of writing is Version 11 Revision 6 (X11R6 ), which was first released in April 1994 and then subsequentially updated in minor versions. Since the release of Version 11, X has virtually taken over as the de facto standard for Unix graphical environments.
Despite its commercial use, the X Window System remains distributable under a liberal license from the Open Group. As such, a complete implementation of X is freely available for Linux systems. X.org , the version most directly based on the X sources, is the version that Linux uses most often. Today, this version supports not only Intel-based systems, but also Alpha AXP, MicroSPARC, PowerPC, and other architectures. Further architectures will follow. Support for innumerable graphics boards and many other operating systems (including Linux) has been added—and X.org implements the latest version, X11R6.8.2.[*]
We should mention here that commercial X Window System servers are available for Linux that may have advantages over the stock X.org version (such as support for certain video cards). Most people use the X.org version happily, though, so this should certainly be your first stop.
As we mentioned in "Why Use a Graphical Desktop?" in Chapter 3, people who run Linux as a server often don't install X at all. They control the server through remote access only, or using just the text interface.
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[*] X.org is a relatively new version. There have been infights in the X Window System community that have led to a split; people have moved from the previously prevailing XFree86 version to the newer X.org version. We will not comment any further on these infights, as they are more a question of personal animosities than of technical benefits.
X Concepts
X is based on a client/server model in which the X server is a program that runs on your system and handles all access to the graphics hardware. An X client is an applications program that communicates with the server, sending it requests, such as "draw a line" or "pay attention to keyboard input." The X server takes care of servicing these requests by drawing a line on the display or sending user input (via the keyboard, mouse, or whatever) to the client application. Examples of X clients are the now-famous image manipulation program GIMP and the many programs coming out of the aforementioned desktop environments KDE and GNOME—for example, the KDE email program KMail.
It is important to note that X is a network-oriented graphics system. That is, X clients can run either locally (on the same system that the server is running) or remotely (on a system somewhere on a TCP/IP network). The X server listens to both local and remote network sockets for requests from clients. This feature is obviously quite powerful. If you have a connection to a TCP/IP network, you can log in to another system over the network and run an X application there, directing it to display on your local X server.
Further advantages of X are security (if the user so desires), modular separation of functions, and support for many different architectures. All this makes the X Window System technically superior by far to all other window systems.
The X Window System makes a distinction between application behavior and window management . Clients running under X are displayed within one or more windows on your screen. However, how windows are manipulated (placed on the display, resized, and so forth) and how they are decorated (the appearance of the window frames) are not controlled by the X server. Instead, such things are handled by another X client called a window manager that runs concurrently with the other X clients. Your choice of window manager will decide to some extent how X as a whole looks and feels. Most window managers are utterly flexible and configurable; the user can select the look of the window decoration, the focus policy, the meaning of the mouse buttons when