Linux Boot-up Sequence

The Linux boot-up sequence basically follows six steps to complete the boot-up sequence. Each step is responsible for (depends on) the next.

Basic Input Output System (BIOS)

  • Searches and executes the boot loader program from the MBR.
  • It is like an abstraction layer between the hardware and the software.

Master Boot Record (MBR)

  • It is located in the first sector of the boot disk. It takes around.
  • Some boot loaders are GRUB, LILO or Linux Loader.


  • Located on a disk partition.
  • It mounts the root file system.
  • It contains drivers for hardware support.
  • It executes the Init program.


The INIT process is responsible for the run-levels:

  1. Halt
  2. Single user mode
  3. Multiuser mode without NFS
  4. Unused, For research purpose
  5. Full multiuser with Graphical mod
  6. Reboot
  7. image