Appendix E: The X Window System

While the heart of Red Hat Linux is the kernel, for many users the face of the operating system is the graphical environment provided by the X Window System, also called simply X.

This appendix is an introduction to the behind-the-scenes world of XFree86, the open-source implementation of X that is provided with Red Hat Linux.

The Power of X

Linux began as a powerful, server-based operating system that excelled at efficiently processing complicated programs that require high CPU resources, as well as handling requests from hundreds or even thousands of clients communicating through network connections. Because of its open nature and stability, however, Linux has quickly developed into a popular GUI-based operating system for workstations, both at home and in the workplace.

In the Unix world, windowing environments have existed for decades, predating many of the current mainstream operating systems. The X Window System is now the dominant graphical user interface (GUI) for Unix-like operating systems.

To create this GUI for the user, X uses a client/server architecture. Specifically, an X server process is started so that X client processes can connect to the X server via a network or local loopback interface. The server process handles the communication with the hardware, such as the video card, monitor, keyboard, and mouse.

The X client exists in the user space, issuing requests to the X server.

On Red Hat Linux systems, the XFree86 server fills the role of the X server. As a large-scale open-source software project claiming hundreds of developers around the world, XFree86 features rapid development, a wide degree of support for various hardware devices and architectures, and the ability to run on different operating systems and platforms.

The X server performs many difficult tasks using a wide array of hardware, requiring detailed configuration. Luckily, most Red Hat Linux desktop users are unaware of the XFree86 server running on their system. They are much more concerned with the particular desktop environment in which they spend most of their time. The Red Hat Linux installation program does an excellent job of configuring your XFree86 server during the installation process, ensuring that X performs optimally when first started.

If some aspect of your system changes, such as the monitor or video card, XFree86 will need to be reconfigured. In addition, if you are troubleshooting a problem with XFree86 that cannot be solved using a configuration utility, such as the X Configuration Tool, you may need to access its configuration file directly.

The X Configuration Tool is capable of configuring XFree86 while the X server is active. To start the X Configuration Tool while in an active X session, click the Main Menu button and choose System Settings > Display. Or, to start the X Configuration tool from the command line (a likely scenario if you can’t get X working), type redhat-config-xfree86 at a command prompt.

After using X Configuration Tool during an X session, you will need to log out of the current X session and then log back in for the changes to take effect.