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Lesson 2The X Windows System
ObjectiveFunction and basic installation of the X Windows System

Basic Installation of the X Windows System

What is the function and basic installation of the X Windows System?
The X Windows System[1] is the foundation for Linux's graphical user interface (GUI). Often referred to as X, the X Windows System provides the necessary tools and functionality to make a GUI. These tools come from a collection of applications found in the various directories under /usr/X11R6/.
GUI layers

Running X applications

Any application that conforms to the X standard can run as an X client, as long as an X server is running. The X server provides the interface between X applications, or "clients," and the video hardware. An additional benefit is that X clients do not need to run on the same machine as the X server. An X server and its clients can be across the world from each other.

X client requests

To minimize overhead, the X server only performs basic display functions. X clients request services from the X server such as:
  1. Display a window
  2. Draw a blue box
  3. Send input to a program
  4. Rastera font

Raster: To apply all transformations (scaling, skewing, rotating, etc.) to a font and display a string of characters on a graphical display.
The server interprets these requests and responds by either granting or refusing the client's request for input or display. If the X server is unable to fill an X application's needs, it notifies the X application that the request is refused.


While it is possible to purchase and install a commercial version of X, Linux comes with XFree86 a freely available X server. XFree86 comes in source form, and it compiles on many different systems. Red Hat Linux provides packages containing the complete XFree86 source, documentation, libraries, binaries, and fonts.

Installing XFree86

XFree86 installs as part of the default installation procedure. If, however, you elect not to install X Windows, XFree86 may be installed later via the rpm or gnoRPM .
Installing XWindows System
The next lesson examines the factors that influence the installation of XFree86.

[1] X Window System: A collection of programs which act as an intermediate layer between X applications and the computer video hardware, keyboard, and mouse.
[2] XFree86: A popular implementation of the X11R6 X Window System standard used by many operating systems. XFree86 is the default X server for Red Hat Linux.