The Init Process - Novell LINUX ENTERPRISE DESKTOP 11 - ADMINISTRATION GUIDE 17-03-2009 Administration Manual

Loading the Installation System or Rescue System
As soon as the hardware has been properly recognized, the appropriate drivers have
been loaded, and udev has created the device special files, init starts the installation
system, which contains the actual YaST installer, or the rescue system.
Starting YaST
Finally, init starts YaST, which starts package installation and system configuration.

9.2 The init Process

The program init is the process with process ID 1. It is responsible for initializing the
system in the required way. init is started directly by the kernel and resists signal 9,
which normally kills processes. All other programs are either started directly by init or
by one of its child processes.
init is centrally configured in the /etc/inittab file where the runlevels are defined
(see Section 9.2.1, "Runlevels"
daemons are available in each of the runlevels. Depending on the entries in /etc/
inittab, several scripts are run by init. By default, the first script that is started after
booting is /etc/init.d/boot. Once the system initialization phase is finished, the
system changes the runlevel to its default runlevel with the /etc/init.d/rc script.
For reasons of clarity, these scripts, called init scripts, all reside in the directory /etc/
init.d (see
Section 9.2.2, "Init Scripts"
The entire process of starting the system and shutting it down is maintained by init.
From this point of view, the kernel can be considered a background process whose task
is to maintain all other processes and adjust CPU time and hardware access according
to requests from other programs.
9.2.1 Runlevels
In Linux, runlevels define how the system is started and what services are available in
the running system. After booting, the system starts as defined in /etc/inittab in
the line initdefault. Usually this is 3 or 5. See
(page 82). As an alternative, the runlevel can be specified at boot time (by adding the
runlevel number at the boot prompt, for instance). Any parameters that are not directly
(page 81)). The file also specifies which services and
(page 84)).
Table 9.1, "Available Runlevels"
Booting and Configuring a Linux System 81