Linux Booting Process

1. Bios

2. MBR: Linux or Grub

3. Kernel

4. Init

5. Run Level

BIOS:

The basic Input/output System is the lowest level interface between the computer

and Peripherals

The bios integrity checks on the memory and seeks instruction on the Master

boot record on the floppy drive or hardware

MBR:

The MBR Points to the boot loader (GRUB or Linux Loader)

The Boot loader will then ask for the OS label which will identify, which kernel to

run and where it is located (hardware and partition specified)

The installation process requires to creation, identification of partition and where

to install the OS.

The boot loader then loads the Linux Operating System.

Kernel

The first thing the kernel does is to execute init program, init is the root/parent of

all process executing on Linux

The first process that init starts is a Script /etc/rc.d/rc.sysinit

Based on the appropriate run-level, scripts are executed to start various process

to run the system and make it function.

The kernel is a program that constitutes the central core of a computer operating

system. It has complete control over everything that occurs in the system.

A kernel can be contrasted with a shell (such as bash, csh or ksh in Unix-like

operating systems), which is the outermost part of an operating system and a

program that interacts with user commands. The kernel itself does not interact

directly with the user, but rather interacts with the shell and other programs as

well as with the hardware devices on the system, including the processor (also

called the central processing unit or CPU), memory and disk drives.

Stage 1 and Stage 2

Stage 1 : The primary boot loader, commonly called Stage 1

The primary boot loader must exist in the very small space allocated for the

MBR.which is less than 512 bytes exactly 460 bytes .Therefore only thing the

primary boot loader accomplishes is loading the secondary boot loader ,due to

fact that there is not enough space in MBR.

Stage 2: Loading the secondary boot loader, commonly called stage 2

The secondary boot loader actually brings up the advanced functionality that

allows you to load a specific operating system.