- BIOS performs POST (Power On Self Test): series of tests run when computer initializes
-Ensures functionality of hardware
- 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
- Kernel initialize the system by loading daemons.
Lilo: legacy boot loader, but can still be fund in industrial world. configuration file: /etc/lilo.conf
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:
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
- 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: