The GRUB configuration file
GRUB can be configured to boot into a graphical menu, allowing the user to bypass the GRUB shell entirely. To display this menu, GRUB needs a specific configuration file, /boot/grub/menu.lst.
The location of this file may be different on your system. For example, on Red Hat systems the default configuration file is /boot/grub/grub.conf.
The configuration file defines various menu options along with the commands required to boot each option. The earlier example of booting a stock Red Hat Fedora 8.0 system could have been accomplished with the following configuration file:
default=0 timeout=3 title Red Hat Linux (2.4.18-14) root (hd0,0) kernel /vmlinuz-2.4.18-14 ro root=/dev/hda2 initrd /initrd-2.4.18-14.img
GRUB has many more features, including serial console support, support for booting other operating systems, and so on. For more information about GRUB, see the info documentation (info grub or pinfo grub) or the online documentation.