A boot loader is a software program
that runs when a computer boot. It's responsible for loading and
transferring control to an operating system kernel software. The kernel,
in turn, initializes the rest of the operating system.
GRUB (GRand Unified Boot-loader) or GNU GRUB
is a very powerful multi-boot loader, which can load a wide variety of
free operating systems, as well as proprietary operating systems with
chain-loading. GRUB is designed to address the complexity of booting a
personal computer. One of the important features in GRUB is flexibility;
GRUB understands filesystems and kernel executable formats, so you can
load an arbitrary operating system the way you like, without recording
the physical position of your kernel on the disk. Thus you can load the
kernel just by specifying its file name and the drive and partition
where the kernel resides.
When booting with GRUB, you can use either a command-line interface or a menu interface.
Using the command-line interface, you type the drive specification and
file name of the kernel manually. In the menu interface, you just select
an OS using the arrow keys. The menu is based on a configuration file
which you prepare beforehand. While in the menu, you can switch to the
command-line mode and vice-versa. You can even edit menu entries before
using them.
Contents of GRUB
Installed programs:grub-bios-setup, grub-editenv, grub-fstest, grub-install, grub-kbdcomp, grub-menulst2cfg, grub-mkconfig, grub-mkimage, grub-mklayout, grub-mknetdir, grub-mkpasswd-pbkdf2, grub-mkrelpath, grub-mkrescue, grub-mkstandalone, grub-ofpathname, grub-probe, grub-reboot, grub-script-check, grub-set-default, grub-sparc64-setup
Installed directories:
/usr/lib/grub, /etc/grub.d, /usr/share/grub, /boot/grub
Short Descriptions
grub-bios-setup Is a helper program for grub-install
grub-editenv A tool to edit the environment block
grub-fstest Tool to debug the filesystem driver
grub-install Install GRUB on your drive
grub-kbdcomp Script that converts an xkb layout into one recognized by GRUB
grub-menulst2cfg Converts a GRUB Legacy menu.lst into a grub.cfg for use with GRUB 2
grub-mkconfig Generate a grub config file
grub-mkimage Make a bootable image of GRUB
grub-mklayout Generates a GRUB keyboard layout file
grub-mknetdir Prepares a GRUB netboot directory
grub-mkpasswd-pbkdf2 Generates an encrypted PBKDF2 password for use in the boot menu
grub-mkrelpath Makes a system pathname relative to its root
grub-mkrescue Make a bootable image of GRUB suitable for a floppy disk or CDROM/DVD
grub-mkstandalone Generates a standalone image
grub-ofpathname Is a helper program that prints the path of a GRUB device
grub-probe Probe device information for a given path or device
grub-reboot Sets the default boot entry for GRUB for the next boot only
grub-script-check Checks GRUB configuration script for syntax errors
grub-set-default Sets the default boot entry for GRUB
grub-sparc64-setup Is a helper program for grub-setup
EDIT GRUB File
GRUB configuration file is located in grub directory. Pathname: /boot/grub/grub.cfg. This file is required when you want to change the order in boot menu.