24.6 X

• X is a client-server GUI system. XFree86 is the X implementation used for Linux.

• An X server is software or hardware that renders graphical output on a display device.

• An X client is software whose output is displayed by an X server and is usually managed by a window manager.

• An X window manager is a client that applies frames and controls to other client windows.

24.6.1 Objective 1: Install and Configure XFree86

24.6.1.1 Selecting and configuring an X server

• XFree86 configuration depends on the software version, the video chipset in use, and the monitor's capabilities.

• XFree86 can be installed from Linux distribution packages (.rpm, .deb), precompiled binaries, or compiled from source.

• Configuration of XFree86 is done in the XF86Config file.

• XF86Config contains sections that define input devices, monitors, graphics modes, and so on.

• XF86Config files differ between XFree86 Versions 3.x and 4.x.

24.6.1.2 X fonts

• The X server uses X fonts to satisfy font requests from X clients.

• Fonts are enumerated either through a static list presented in /etc/X11/XF86Config or through a font server such as xfs.

• xfs is configured using its configuration file, /etc/X11/fs/config.

24.6.1.3 .Xresources

• X resource settings in the .Xresources file control client program parameters. For example, this line defines a black background for an xterm:

xterm*background: Black

24.6.2 Objective 2: Set Up xdm

• xdm, the X Display Manager, handles X sessions on physical displays both locally and across the network.

• xdm handles authentication.

• xdm is configured by a series of files in /etc/X11/xdm.

• xdm is typically started automatically in runlevel 5 by making the appropriate settings in /etc/inittab.

• xdm may be personalized by changing the resources in /etc/X11/xdm/ Xresources.

• Command-line options for the X server can be added to the /etc/X11/xdm/Xservers file.

24.6.2.1 X stations

• X stations, also known as X terminals, are low-cost hardware systems that implement an X server and display.

• xdm can listen for inbound connection requests from X terminals using the xdmcp protocol.

• Specific access rules for X terminals to the xdm daemon can be configured in /etc/X11/xdm/Xaccess.

24.6.3 Objective 3: Identify and Terminate Runaway X Applications

• X applications can occasionally become unresponsive or remain running after the X server is terminated.

• Use the top utility to identify processes.

• Use kill or killall to terminate processes.

• If the X server is unresponsive, use Ctrl-Alt-F2 to switch to another console, and kill offending processes.

24.6.4 Objective 4: Install and Customize a Window Manager

• An X server doesn't supply a working user environment.

• Starting X usually involves launching not only the X server but also a window manager and other clients.

• A default window manager, such as the basic twm, is started by a combination of the startx script and xinit.

• xinit also calls scripts that include a window manager and default clients.

• Default system X configuration can be overridden by files in the user's home directory.

24.6.4.1 Window managers

• Each window manager and desktop environment has its own style of configuration.

• twm uses .twmrc in the user's home directory. If that file doesn't exist, it uses the systemwide /etc/X11/twm/system.twmrc.

• Window manager configuration files can contain font and color selections, bindings between actions (such as mouse clicks) and responses, and menu definitions.

24.6.4.2 xterm

• A terminal emulator is a program that offers a command-line interface in a GUI window.

• xterm is the standard terminal emulator; there are many others.

• xterm can be configured in /usr/lib/X11/app-defaults/XTerm.

24.6.4.3 X libraries

• X applications are dependent upon shared X libraries.

• Various graphical toolkits such as GTK or Qt can be used to develop X client applications.

• Software that depends on a particular library will not run unless that library is installed.

• You can determine which libraries an executable requires with ldd .

24.6.4.4 Remote X clients

• X clients can be displayed on remote X servers.

• The DISPLAY environment variable is used to indicate the destination for X client displays.

• DISPLAY has the format [host]:display[. screen] where host is a remote hostname or IP address, display is the display target (starting with 0), and screen is the screen to use on multiheaded displays.

• DISPLAY must be exported.