Linux Boot Process Stages

Hello,

Herewith I am posting "Linux Boot Process" in such an easy way so that you can understand it properly.

1) First stage is obviously called "POST"
(POST = Power On Self Test, Means if you get "beep" sound, the computer hardware is working properly i.e. your electronic circuit)

2) BIOS

3) MBR = Master Boot Record. Having size of 512 Bytes. The Byte distribution inside MBR is,

446 Bytes = Primary Boot Loader
64 Bytes = Partition Table
2 Bytes = MBR Validation Check

4) Loading Linux Loader called GRUB (GRand Unified Boot Loader)
(Please note that /etc/grub/grub.conf is linked with /boot/grub/grub.conf"

5) Kernel Loads. The sub processes are,

* Mounts the "/root" file system
* PID of this process would be "1"
* "initrd" (Initial RAM Disk), used by kernel as a temporary "root" file system until kernel is boot properly & the real "root" file system is mounted.

"initrd" contains necessary drivers to load.

6) "init" process loads entries mentioned inside "/etc/inittab" & "/etc/rc.sysinit" files.

7) "runlevel" loads the respective files & service mentioned inside "/etc/rc.d/rc*.d/
* There are total 6 runlevel are available by default.
* If you set "runlevel 5" in "/etc/inittab", then it will load all drivers & services available inside
"/etc/rc.d/rc5.d/

"S" letter shows (Service to start during "startup")
"K" letter shows (Service to kill during "startup")

That's it.

So, in short Linux boot stages are,
POST, BIOS,MBR,Kernel,INIT & Runlevel

EOF