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106 Chapter 7. X Servers and Clients

you must already be logged into the system at runlevel 3 to be able to type commands, startx is only

designed to bring up certain X clients, such as a desktop environment, in a particular manner. It does

not provide any user authentication.

When startx begins, it looks for a .xinitrc ﬁle in the user’s home directory to deﬁne the X clients

to run. If it does not ﬁnd that ﬁle present, it will run the system default /etc/X11/xinit/xinitrc

script instead. The startx script then does the same thing with the .xserverrc ﬁle, looking for

it in the user’s home directory and then running the default /etc/X11/xinit/xserverrc script if

it cannot be found. Since many different X clients exist, the xinitrc ﬁles are very important. The

xserverrc script is less important. It only sets the X server to connect to the X clients. Since the

default X server is already conﬁgured with the /etc/X11/X link, Red Hat Linux does not install a

default xserverrc.

The default xinitrc script then looks for user-deﬁned ﬁles and default system ﬁles, including .Xre-

sources, .Xmodmap, and .Xkbmap in the user’s home directory and Xresources, Xmodmap, and

Xkbmap in the /etc/X11/ directory. The Xmodmap and Xkbmap ﬁles, if they exist, are used by the

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.

7.4.2. 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

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Red Hat LINUX 7.2 - OFFICIAL LINUX CUSTOMIZATION GUIDE Guida di Installazione Pagina 106

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Red Hat LINUX 7.2 - OFFICIAL LINUX CUSTOMIZATION GUIDE Guida di Installazione Pagina 106

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