Grand Unified Boot loader (GRUB)

GRUB

• GRUB is an operating system independent boot loader
• A multiboot software packet
• Flexible command line interface
• File system access
• Support multiple executable format
• Support diskless system
• Download OS from network
• GNU GRUB is a Multiboot boot loader.
• It was derived from GRUB, the GRand Unified Bootloader, which was originally designed and implemented by Erich Stefan Boleyn.
• Briefly, a boot loader is the first software program that runs when a computer starts.
• It is responsible for loading and transferring control to the operating system kernel  software
• The kernel, in turn, initializes the rest of the operating system

GRUB boot process

• The BIOS finds a bootable device (hard disk) and transfers control to the master boot record
• The MBR contains GRUB stage 1. Given the small size of the MBR, Stage 1 just load the next stage of GRUB

   

• GRUB Stage 1.5 is located in the first 30 kilobytes of hard disk immediately following the MBR. Stage 1.5 loads Stage 2.
• GRUB Stage 2 receives control, and displays to the user the GRUB boot menu (where the user can manually specify the boot parameters).
• GRUB loads the user-selected (or default) kernel into memory and passes control on to the kernel.

GRUB Config File

GRUB 2

• Derived from PUPA (Published Unexamined Patent Application) research project, Japan
• Next generation of GRUB
• Rewritten from scratch to clean up everything for modularity & portability
• Goals:
  • Scripting support
  • Graphical Interface
  • Dynamic loading of modules
  • Portability for various architecture
  • Internationalization
  • Real memory management
  • Object-oriented framework for file system
  • Cross platform installation
  • Fix design mistakes in GRUB legacy