C.3. X Server Configuration Files

The X server is a single binary executable /usr/bin/Xorg; a symbolic link X pointing to this file is also provided. Associated configuration files are stored in the /etc/X11/ and /usr/share/X11/ directories.
The X Window System supports two different configuration schemes. Configuration files in the xorg.conf.d directory contain preconfigured settings from vendors and from distribution, and these files should not be edited by hand. Configuration in the xorg.conf file, on the other hand, is done completely by hand but is not necessary in most scenarios.

Note

All necessary parameters for a display and peripherals are auto-detected and configured during installation. The configuration file for the X server, /etc/X11/xorg.conf, that was necessary in previous releases, is not supplied with the current release of the X Window System. It can still be useful to create the file manually to configure new hardware, to set up an environment with multiple video cards, or for debugging purposes.
The /usr/lib/xorg/modules/ (or /usr/lib64/xorg/modules/) directory contains X server modules that can be loaded dynamically at runtime. By default, only some modules in /usr/lib/xorg/modules/ are automatically loaded by the X server.
When Red Hat Enterprise Linux 6 is installed, the configuration files for X are created using information gathered about the system hardware during the installation process by the HAL (Hardware Abstraction Layer) configuration back end. Whenever the X server is started, it asks HAL for the list of input devices and adds each of them with their respective driver. Whenever a new input device is plugged in, or an existing input device is removed, HAL notifies the X server about the change. Because of this notification system, devices using the mouse, kbd, or vmmouse driver configured in the xorg.conf file are, by default, ignored by the X server. See Section C.3.3.3, “The ServerFlags section” for further details. Additional configuration is provided in the /etc/X11/xorg.conf.d/ directory and it can override or augment any configuration that has been obtained through HAL.

C.3.1. The Structure of the Configuration

The format of the X configuration files is comprised of many different sections which address specific aspects of the system hardware. Each section begins with a Section "section-name" line, where "section-name" is the title for the section, and ends with an EndSection line. Each section contains lines that include option names and one or more option values. Some of these are sometimes enclosed in double quotes (").
Some options within the /etc/X11/xorg.conf file accept a Boolean switch which turns the feature on or off. The acceptable values are:
  • 1, on, true, or yes — Turns the option on.
  • 0, off, false, or no — Turns the option off.
The following shows a typical configuration file for the keyboard. Lines beginning with a hash sign (#) are not read by the X server and are used for human-readable comments.
# This file is autogenerated by system-setup-keyboard. Any 
# modifications will be lost.

Section "InputClass"
  Identifier  "system-setup-keyboard"
  MatchIsKeyboard "on"
  Option    "XkbModel"  "pc105"
  Option    "XkbLayout" "cz,us"
# Option    "XkbVariant"  "(null)"
  Option    "XkbOptions"  "terminate:ctrl_alt_bksp,grp:shifts_toggle,grp_led:scroll"
EndSection