Super Grub Disk (SGD) is a specialty rescue CD for emergency repairs on boot sectors. Despite its name, SGD not only manipulates the Grand Unified Bootloader (GRUB), but also works with the content of other master boot records as well. Available in English, French, and Castillian Spanish, SGD also works with a variety of operating systems and supports all the basic options needed to manipulate how a hard drive boots.

In order for the BIOS to load an OS it looks for instructions on the first sector of a hard drive. On the first sector of the hard drive resides the master boot record (MBR), and is where a boot loader is initialized. Depending on the boot loader, additional files may be stored and read from a partition on the hard drive. After this step the boot loader begins to start the operating system, and is not used again until the next boot. If the computer has only one operating system, the boot loader may not ask for user input. Because of this, many people do not realize they have a boot loader installed.

GRUB is not dependent upon any operating system. It was written to conform with the Free Software Foundation's Multiboot Specification, which allows it to boot almost any operating system. In fact, it can boot multiple operating systems on computers that have more than one installed on their hard drives. Among GRUB's features:

If you discover that a certain application no longer works for you, you can go back to a previous kernel to try to run your program. GRUB, the boot loader found in most Linux distributions, lets you choose among operating systems and kernels installed on your box. Many people, however, fear that messing with GRUB may ruin their system, because of its many esoteric options, and configuration file text that often contains no help comments. QGRUBEditor can help you view and edit the GRUB boot loader from a graphical user interface.

LILO (Linux Loader) and GRUB (GRand Unified Bootloader) are both configured as a primary boot loader (installed on the MBR) or secondary boot loader (installed onto a bootable partition). Both work with supporting operating systems such as Linux, FreeBSD, Net BSD, and OpenBSD. They can work with unsupported operating system, such as Microsoft Windows XP, in the configuration file. Both allow users—root users—to boot into single-user-mode.

LILO (Linux Loader) and GRUB (GRand Unified Bootloader) are both configured as a primary boot loader (installed on the MBR) or secondary boot loader (installed onto a bootable partition). Both work with supporting operating systems such as Linux, FreeBSD, Net BSD, and OpenBSD. They can work with unsupported operating system, such as Microsoft Windows XP, in the configuration file. Both allow users—root users—to boot into single-user-mode.

Most simply, a boot loader loads the operating system. When your machine loads its operating system, the BIOS reads the first 512 bytes of your bootable media (which is known as the master boot record, or MBR). You can store the boot record of only one operating system in a single MBR, so a problem becomes apparent when you require multiple operating systems. Hence the need for more flexible boot loaders.

GRUB gobbles up LILO any day of the week. It is faster to load, more resiliant to configuration errors, and more secure when you try to lock down the config using boot password. However, it does have two missing features:

1. LILO -R

on Lilo, this changes the default for the next reboot only.

Grub is a world-class boot loader with insufficient documentation. In many ways it blows the doors of LILO. For instance, it's MUCH easier to use Knoppix to rebuild a grub boot loader than to rebuild a LILO boot loader. However, until you're comfortable with grub, it might seem just the opposite. All too often grub dumps you at a grub> prompt with no hint of what you should do. You might have heard that a successful reboot is just three commands away, but which commands? The state of grub's documentation is such that you can't figure it out unless you already know grub.

The GRUB boot loader is the default boot loader installed by Red Hat Enterprise Linux (and other distributions such as SUSE Linux Enterprise Server, Mandriva, Fedora Core and Gentoo, amongst others).

This article assumes you are using GRUB as your bootloader, and that you have an existing, working, and bootable installation of Linux. This document (should) contain every command required to convert a single drive over to a fully mirrored RAID-1 system. During the process, you will have an opportunity to change the filesystem type (perhaps from Ext2 to XFS or ReiserFS); I will be migrating partitions from Ext2 to Ext3 and XFS.

Why use GRUB instead of LILO? Well, if you're reading this HOWTO, you're likely to already have your reasons for switching. But to give a couple quick reasons, you only install GRUB in your MBR once, it doesn't need to be reinstalled each kernel change like LILO, and you can also edit the boot entries, etc. from GRUB itself without having to boot first and change the config file. These are just some of my reasons, you can find more for yourself - but how do you set it up the Debian way? This HOWTO will show you how to install the GRUB bootloader, configure it, create GRUB boot floppies and keep your GRUB configuration up to date with your latest installed kernels easily.