The Init Process - Novell LINUX ENTERPRISE SERVER 10 SP2 - INSTALLATION AND ADMINISTRATION Installation Manual

process are written to INITRD_MODULES in /etc/sysconfig/kernel.
These names are used to generate a custom initramfs that is needed to boot the
system. If the modules are not needed for boot but for coldplug, the modules are
written to /etc/sysconfig/hardware/hwconfig-*. All devices that are
described with configuration files in this directory are initialized in the boot process.
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.

20.2 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 20.2.1, "Runlevels" (page 393)). The file also specifies which services and
daemons are available in each of the levels. Depending on the entries in /etc/
inittab, several scripts are run by init. For reasons of clarity, these scripts, called
init scripts, all reside in the directory /etc/init.d (see Section 20.2.2, "Init Scripts"
(page 396)).
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.
20.2.1 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
Booting and Configuring a Linux System 393