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Boot process
  1. BIOS performs POST  (Power On Self Test): series of tests run when computer initializes
    -Ensures functionality of hardware
  2. Boot loader: program used to load an OS.
    -Locates and executes the kernel of the OS.
    MBR might contain pointer to a partition containing a boot loader on the first sector
    Active partition: partition pointed to by MBR.One per HDD
  3. Kernel initialize the system by loading daemons.boot process

Lilo: legacy boot loader, but can still be fund in industrial world. configuration file: /etc/lilo.conf

Grub:

Stage1: first major part of GRUB
-Typically resides on MBR/GPT
-Remaining parts of the boot loader (Stage1.5 and Stage2) reside in the /boot/grub directory
Stage1.5: loads filesystem support and Stage2
Stage2: performs the actual boot loader functions, displays graphical boot loader screen.

Configuration file: /boot/grub/grub.conf

Fix the damaged GRUB: grub-install /path

GRUB2:

Does not supersede GRUB, a standalone version. Used by modern Linux system.

step1. Edit configuration file : /etc/default/grub

  • GRUB_TIMEOUT=5 : 5 second for the user to choose the boot options
  • GRUB_DEFAULT=saved
    • Saved means remember the OS been chosen last time and do the same choice
    • 0, 1, 2 so forth, first one in the menu is 0.

Step 2, use grub2-mkconfig command to rebuild the /boot/grub/grub.cfg

Fix the damaged GRUB2 boot loader: grub2-install /path