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Chapter 6. The X Window System

xmodmap

utility to configure the keyboard. The

Xresources

files are read to assign specific prefer 

ence values to particular applications.

After setting these options, the

xinitrc

script executes all scripts located in the

/etc/X11/xinit/xinitrc.d/

directory. One important script in this directory is

xinput

, which

configures settings such as the default language to use and the desktop environment to start from

(

/etc/sysconfig/desktop

).

Next, the

xinitrc

script tries to execute

.Xclients

in the user's home directory and turns to

/etc/X11/xinit/Xclients

if it cannot be found. The purpose of the

Xclients

file is to start the

desktop environment or, possibly, just a basic window manager. The

.Xclients

script in the

user's home directory starts the user specified desktop environment or window manager in the

.Xclients default

file. If

.Xclients

does not exist in the user's home directory, the standard

/etc/X11/init/Xclients

script attempts to start another desktop environment, trying GNOME

first and then KDE. If a desktop environment cannot be found by this point,

Xclients

attempts the

default window manager listed in the

.wm_style

file in the user's home directory. If this fails, it

cycles through a predefined list of window managers.

The preferred X client applications should now have started by this point, along with the XFree86

server. If you need more details concerning starting X in runlevel 3, refer to the

startx

and

xinit

man pages and read through the scripts named above.

6.4.2. Runlevel 5:

prefdm

Runlevel 5 uses a slightly different method to start X. When the system starts, no one is logged into

the system by default. In order for a user to start a session, they must log in to the system. In runlevel

5, users authenticating themselves at the console use a display manager, a special X client that allows

the user to submit their login name and password.

Depending on the desktop environments installed on your specific Red Hat Linux system, three dif 

ferent display managers are available to handle the user authentication. The

xdm

display manager is

the original X authentication tool.

xdm

only allows you to log in and start an X session, nothing more.

The

gdm

display manager, designed to work with the GNOME desktop environment, and

kdm

display

manager, used with the KDE desktop environment, allow you to set the desktop environment, or ses 

sion, you would like to use after authentication. Additionally, you can restart or halt the system from

the login screen. The

gdm

display manager also allows you to configure the language you would like

to use.

When the system enters runlevel 5, a line in the

/etc/inittab

file specifies that the

prefdm

script is

executed in order to determine the preferred display manager to bring up for user authentication. The

prefdm

script uses the preferences stated in the

/etc/sysconfig/desktop

file to find the proper

display manager. If no desktop environment is specified,

prefdm

cycles through the

gdm

,

kdm

, and

xdm

display managers to find one to use. Once one is found,

prefdm

launches it to handle the user

login.

Each of the display managers look to the

/etc/X11/xdm/Xsetup_0

file to set up the login screen.

Once the user logs into the system, the

/etc/X11/xdm/GiveConsole

script runs to assign own 

ership of the console to the user. Then, the

/etc/X11/xdm/Xsession

script runs to accomplish

many of the tasks normally done by the

xinitrc

script when starting X in runlevel 3, including set 

ting system and user resources, as well as running the scripts in the

/etc/X11/xinit/xinitrc.d/

directory.

The user can specify which desktop environment they want to utilize when they authenticate using the

gdm

or

kdm

display managers by selecting it from the Session menu. If the desktop environment is not

specified in the display manager, the

/etc/X11/xdm/Xsession

script will check the

.xsession

and

.Xclients

files in the user's home directory to decide which desktop environment to load. As a

last resort, the

/etc/X11/xinit/Xclients

file is used to select a desktop environment or window

manager to use in the same way as runlevel 3.