LINUX BOOT PROCESS

There are 6 high level stages of a typical Linux boot process.


1)BIOS
  • Performs some system integrity checks.
  • Searches, loads, and executes the boot loader program.
  • It looks for boot loader in floppy,cd-rom, or  hard drive.
  • Once the boot loader program is detected and loaded into the memory, BIOS gives the control to it.
  • BIOS loads and executes the MBR boot loader.
2)MBR
  • It stands for Master Boot Record.
  • It is loacated in the !st sector of the bootable disk.
  • MBR is less than 512 bytes in size.
  • The contains information about GRB.
  • MBR loads and executes the GRB boot loader.
3) GRUB
  • GRUB stands for Grand Unified Bootloader.
  • GRUB displays a splash screen, waits for few seconds, if you dont enter anything, it loads the default kernel image as specified in the grub configuration file
 4)Kernel
  • Mounts the root file system.
  • Kernel executes the /sbin/init program.
5) Init
  • Init identifies the  default initlevel from /etc/inittab and uses that to load all appropriate program. It has run levels as follows:-0-halt,1-Single user mode,2-Multiuser,3-Full multiuser mode,4-Unused,5-x11,6-Reboot
6)Runlevel programs
  •  When the Linux system is booting up, there are various services getting started. 
  • Programs starts with S are used during startup
  • Programs starts with K are used for shutdown.

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