Operation Manual
Loading the Installation System or Rescue System
As soon as the hardware is properly recognized, the appropriate drivers are loaded,
and udev creates the special device les, init starts the installation system with the
actual YaST installer, or the rescue system.
Starting YaST
Finally, init starts YaST, which starts package installation and system conguration.
16.2 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 congured in the /etc/inittab le where the runlevels are dened
(see Section 16.2.1, “Runlevels” (page 231)). The le also species which services and
daemons are available in each of the runlevels. Depending on the entries in /etc/
inittab, several scripts are run by init. By default, the rst script that is started after
booting is /etc/init.d/boot. Once the system initialization phase is nished, 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 16.2.2, “Init Scripts” (page 234)).
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 to maintain
all other processes and adjust CPU time and hardware access according to requests
from other programs.
16.2.1 Runlevels
In Linux, runlevels dene how the system is started and what services are available in
the running system. After booting, the system starts as dened in /etc/inittab in
the line initdefault. Usually this is 3 or 5. See Table 16.1, “Available Runlevels”
(page 232). As an alternative, the runlevel can be specied at boot time (by adding the
runlevel number at the boot prompt, for instance). Any parameters that are not directly
Booting and Conguring a Linux System 231