Installation
A key feature of GRUB is that it can be installed without being attached to an operating system. However, it needs a copy of a Linux image for such an installation. Working as a stand alone system it is virtually a mini system in its own right and able to boot all the installed major operating systems by chain loading, as described above.
Unlike Linux Loader (LILO), there is no need to reinstall GRUB to the MBR or a partition after changes to the configuration file.
In Linux, the "grub-install" command is used to install stage1 to either the MBR or a partition. GRUB's configuration file, stage2 (usually), and other files must be in a usable partition. If these files or the partition become unavailable, stage1 will drop the user to the command line interface.
The name and disk location of the GRUB configuration file varies from system to system. For example, in openSUSE and (for GRUB legacy) in Debian GNU/Linux the file is stored in /boot/grub/menu.lst while Fedora, Gentoo Linux, and (for GRUB 2) Debian use /boot/grub/grub.conf or ../grub.cfg. Fedora also provides a symbolic link from /etc/grub.conf to /boot/grub/grub.conf for FHS compatibility reasons.
GRUB can be installed on removable media, such as an optical drive (BIOS access, and El Torito), floppy disk or USB flash drive, in order to bring up a system that may not have or cannot boot from a hard disk.
Read more about this topic: GNU GRUB