A tutorial for beginners who are curious to learn about the Linux boot process. If you have any more doubts, you can contact me through my email given in the slide, or through my blog: mastro77.blogspot.in

1. Linux Boot Process
~ Archana Chandrasekharan
Email: kcarchana77@gmail.com

2. Ever wondered what
happens when you switch on
your system until the Login
Page of your Linux OS???

3. SMPS
● Switching Mode Power Supply
● Converts AC to DC
● Provides voltage to Motherboard

4. Bootstrapping
● Loads basic software into memory of
computer
● Executes JUMP command
● Tells the location of BIOS program in ROM

5. Steps towards a
successful login page

6. Step 1: BIOS
● Basic Input/Output System
● Executes MBR
● Looks for Bootloader in HDD/external device

7. Step 2: MBR
● Found in /dev/sda or /dev/hda
● Size: < 512 bytes
● Contains info about GRUB
● Executes GRUB bootloader

8. Step 3: GRUB
● GRand Unified Bootloader
● Can choose which kernel to be executed
● Displays a screen for a few seconds
● Default kernel image: /boot/grub/grub.
cfg

9. grub.cfg
● GRUB configuration file
● Has linux and initrd image

11. /initrd
● INITial RamDisk
● Way to load RAMdisk using Bootloader

13. Step 4: Kernel
● Mounts the root file system
● Executes /sbin/init

14. Step 5: init
● init daemon starts processes from
/etc/inittab
● init identifies default init level and uses
to load appropriate program

15. /etc/inittab
● id:rstate:action:process
● id - identifier of the entry
● rstate - lists the runlevels
● action - which action to be taken
● process - process to start, monitor or
restart if terminated

16. Run levels
6 run levels:
● 0 - halt
● 1 - Single user mode
● 2 - Multiuser without NFS
● 3 - Full Multiuser mode
● 4 - unused
● 5 - X11
● 6 - Reboot

17. When not in quite
mode, you can see a lot
messages while booting.

19. These are the
runlevel programs
executed from the
runlevel directory

20. Runlevel programs
● Run level 0 – /etc/rc.d/rc0.d/
● Run level 1 – /etc/rc.d/rc1.d/
● Run level 2 – /etc/rc.d/rc2.d/
● Run level 3 – /etc/rc.d/rc3.d/
● Run level 4 – /etc/rc.d/rc4.d/
● Run level 5 – /etc/rc.d/rc5.d/

21. /etc/rc.d/rc*.d
● rc scripts are run control scripts
● Programs which starts with S are used for
Startup
● Programs which starts with K are used for
Shutdown

22. Next time when you
boot remember me and
these steps :P

23. References:
● http://mastro77.blogspot.in/2014/09/have-you-
ever-wondered-what-happens.html
● http://mastro77.blogspot.in/2014/09/initrd.
html