GRUB

GRUB, GRand Unified Bootloader is a powerful bootloader that can load multiple operating systems with chain loading. GRUB is designed to address the complexity of booting a personal computer. It supports a wide variety of OS like Linux, DOS, Windows or BSD. During boot-up, the user can select any required operating system to run.

GRUB is based on an earlier multi-boot package and is most often used on Unix-like systems, including GNU, Linux and Solaris. One can easily configure the GRUB dynamically. This means that the user can make changes and write new boot sequences using a command line i.e. during the boot time. These changes include changing the existing boot entries, selecting different kernels, adding new custom entries, or modifying initrd etc.

In addition it even supports data access in Logical Block Address mode. This means that if your computer has modern BIOS, which is capable of accessing more than 8GB i.e. first 1024 cylinders of hard disk space; even then GRUB is able to access all of it automatically.

Booting with GRUB

GRUB can be easily run from or installed to any device like floppy disk, CD-ROM, hard disk, USB drive or any network drive and can load operating systems from many locations, including network drives. When booting with GRUB, you can use either a command-line interface or a menu interface.

When the command-line interface is used, the user has to type the drive specification and file name of the kernel manually.
With the menu interface user can select an OS using the arrow keys and the menu is based on a configuration file which is also prepared by the user earlier.

However, one can easily switch between these interfaces. While in the menu interface, user can switch to the command-line mode, and vice-versa. In addition, you can even edit all the menu entries before using them.

Purpose of Designing GRUB

One of the primary requirement or goals for developing the GRUB is to make the bootloader to be compliant with the Multi-boot Specification. Some of the other goals are as listed below:

To make all the basic functions available directly for the end-users
Support a human-readable text configuration file with preset boot commands
Provide numerous functionalities that support the kernel experts and designers
Ensure backward compatibility of the boot loader for booting the FreeBSD, NetBSD, OpenBSD, and Linux

Features of GRUB

One of the important features of GRUB is its flexibility it is compatible with all file systems and kernel executable formats. Hence, the user can load an arbitrary operating system as needed, even without recording the physical position of your kernel on the disk. Due to this the user can easily load the kernel just by specifying its file name and the drive and partition where the kernel resides. Some of the other features of GRUB are:

Supports an unlimited number of boot entries
Can decompress operating systems before launching them
Has the capability to load the operating systems from various locations, including networks
Each time the configuration file is changed user ned not re-write the GRUB
There are implementations that support Windows and DOS
Possess highly interactive command interface

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