Linux Boot Process

As many people have often wondered, how does the Linux/Unix operating system boot? How could I put in a process to run during boot so that I do not have to start it every time manually? To do this one has to understand the basic environment procedure that is currently in place to add anything to it.

“Linux for Future Technology”

On a typical Linux system, I prefer Debian, the bootloader points to the kernel which in turn points to a file under /etc known as inittab. The interaction between the bootloader and the kernel is complex enough for another article.

  1. The /etc/inittab is a file that contains a set of instructions to call a specific directory under the /etc directory. It is a Shell script that looks something like this:# /etc/inittab: init(8) configuration.
    # $Id: inittab,v 1.91 2002/01/25 13:35:21 miquels Exp $

    # The default runlevel.
    id:2:initdefault:

    # Boot-time system configuration/initialization script.
    # This is run first except when booting in emergency (-b) mode.
    si::sysinit:/etc/init.d/rcS

  2. The system then calls the /etc/init.d/rcS shell script. This script then executes each shell script found in /etc/rcS.d/ directory. When an application