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)

Master Boot Record (MBR)

KERNEL

INIT PROCESS

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