The Debian GNU/Linux kernel loads init very early on in the boot process, using /etc/inittab as its configuration file. This file defines the default run level and what should be done for each run level.
If you have a look at the processes running on your system (with the command line ps or with the graphical Gnome utility gtop) you will see that the init process has process identifier of 1 (unless you are running a more secure GNU/Linux where random numbers are assigned to the processes).
The initialisation table (/etc/inittab) is where system initialisations occur. This table consists of records with four fields separated by a colon:
The first field is an identifier. The second lists the runlevels for which this record is relevant. The third is the action to be performed. The fourth is the command to be run.
In this chapter we look at how the GNU/Linux system is initialised. See Chapter 12 for an explanation of the boot process and how to control booting.