How does Linux server Boot up: Beginners Guide

Booting process is a process that loads to starts the operating system. We will see about each components involved in booting process in this article.

Introduction :

Booting process is the starting process of linux operating system from the point when user switches on the power button of cpu.

Linux Booting process has six steps


2, MBR

3, Grub

4, Kernet

5, init

6, runlevel




Post is Power on self test.

It is a program which has written inside and it used for Diagnostic check.

Plug and Play BIOS:

BIOS used to load the drivers


BSL is Bootstrap Loader

BSL reads the MBR[Master Boot Record]


MBR is available in the first sector of hard disk

Size of MBR is 512MB

MBR contains,

1, Executable codes called master boot codes – 446MB

2, Partition table Information – 64MB

3, Magic number [MBR Validation] – 2MB

MBR reads and executes the Boot Loader.


Grub is GRand Unified Bootloader

=> The GNU operating system uses GNU GRUB as its boot loader

=> Grub is present in /boot/grub/grup.conf

=> Latest version of Grub is Grub version 2.

=> Grub contains kernel and init informations [initramfs].


=> Kernel is the core of operating system

=> It used to interface hardware and software.


=> init is the first command which runs on a Linux operating system /sbin/init.

=> init also contains the process which we installed in system

=> init selects the runlevel


runlevel is the present state of operating system.

We have seven runlevels

We can change the default runlevel from /etc/inittab


0 – System halt; [shut down]

1 – Single user; rarely used.

2 – Multiple users; Multi user mode with NFS [Networking]

3 – Multiple users, command line interface; the standard runlevel for most Linux-based

Operating Systems

4 – User-definable

5 – Multiple users, GUI (graphical user interface); the standard runlevel for most Linux- based desktop systems.

6 – Reboot

Use the following command to change runlevel suddenly

# init <runlevel>

Use the following commandto check the current runlevel, use

# runlevel

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About Dinesh Sobitharaj C

An IT professional having multiple years of experience in IT Infrastructure planning, System integrations, Project implementation and delivery. Devops Enthusiast skilled with broad ranges of technology adoption. Well versed with Cloud Computing and Application Service Offerings such as SaaS/PaaS/IaaS. Expert in aligning business goals, mission and process to architect innovative solutions and strategies.

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