60

Chapter 3. Boot Process, Init, and Shutdown

After the

init

command has progressed through the appropriate

rc

directory for the runlevel, the

/etc/inittab

script forks a

getty

process for each virtual console (login prompts) allocated to the

runlevel. Runlevels 2 through 5 get all six virtual consoles, while runlevel 1 (single user mode) gets

only one and runlevels 0 and 6 get none. The

getty

process opens communication pathways to tty

devices

4

, sets their modes, prints the login prompt, gets the user name, and initiates the login process

for the user.

In runlevel 5,

/etc/inittab

runs a script called

/etc/X11/prefdm

. The

prefdm

script runs the

preferred X display manager,

gdm

if you are running GNOME or

kdm

if you are running KDE, based

on the contents of the

/etc/sysconfig/desktop/

directory.

Finally, the

init

command runs the

/etc/rc.d/rc.local

script.

At this point, you should be looking at a login prompt.

3.3. Running Programs at Boot Time

The file

/etc/rc.d/rc.local

script is run by the

init

command at boot time, or when changing

runlevels, after all other initialization is complete. You can use this file to add additional commands

necessary for your environment. For instance, you can start additional daemons or initialize a printer.

In addition, if you require serial ports setup at boot time, you can create and edit

/etc/rc.serial

.

This script runs

setserial

commands to configure the system's serial ports. See the

setserial

man page for more information.

3.4. Differences in the Boot Process of Other Architectures

Once the Red Hat Linux kernel loads and hands off the boot process to the

init

command, the same

sequence of events occurs on every architecture. So the main difference between each architecture's

boot process is in the application used to find and load the kernel.

For example, the Alpha architecture uses the

aboot

boot loader, while the Itanium architecture uses

the ELILO boot loader.

Consult the Official Red Hat Linux Installation Guide specific to these platforms for information on

configuring their boot loaders.

3.5. SysV Init

The SysV init is a standard process used by Red Hat Linux to control which software the

init

com 

mand launches or shuts off on a given runlevel. SysV init chosen because it is easier to use and more

flexible than the traditional BSD style init process.

The configuration files for SysV init are in the

/etc/rc.d/

directory. Within this directory, are the

rc

,

rc.local

, and

rc.sysinit

scripts as well as the following directories:

init.d

rc0.d

rc1.d

rc2.d

rc3.d

rc4.d

rc5.d

rc6.d

4. See Section 2.3.11 for more information on tty devices.