Red Hat LINUX 7.2 Reference Manual page 36

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and is always available for use. The BIOS provides the lowest level interface to peripheral devices
and controls the first step of the boot process.
The BIOS tests the system, looks for and checks peripherals, and then looks for a drive to use to
boot the system. Usually, it checks the floppy drive (or CD-ROM drive on many newer systems) for
bootable media, if present, and then it looks to the hard drive. The order of the drives used for booting
is usually controlled by a particular BIOS setting on the system. Once Red Hat Linux is installed on
a hard drive of a system, the BIOS looks for a Master Boot Record (MBR) starting at the first sector
on the first hard drive, loads its contents into memory, and passes control to it.
This MBR contains instructions on how to load the boot loader, GRUB orLILO (LInux LOader),
depending on the boot loader you installed. The MBR then loads the boot loader, which takes over
the process (if the boot loader is installed in the MBR). In the default Red Hat Linux configuration,
GRUB or LILO uses the settings in the MBR to display boot options and allow for user input on which
operating system to actually start up.
But this begs the question: How does the boot loader in the MBR know what to do when the
MBR is read? LILO actually has already written the instructions there through the use of lilo
with the /etc/lilo.conf configuration file. GRUB has also written the instructions in the
/boot/grub/grub.conf configuration file. For more information about GRUB, see Chapter 5,
GRUB.
3.2.1 Options in /etc/lilo.conf
Most of the time, you will have no need to change the Master Boot Record on your hard drive un-
less you need to boot a newly installed operating system or are looking to use a new kernel. If you
do need to create a new MBR using LILO but using a different configuration, you will need edit
/etc/lilo.conf and run lilo again.
If you are planning to edit /etc/lilo.conf, be sure to make a backup
copy of the file before making any changes. Also, be sure that you have a
working boot floppy available so that you will be able to boot the system
and make changes to the MBR if there is a problem. See the man pages
for mkbootdisk for more information on creating a boot disk.
The file /etc/lilo.conf is used by lilo to determine which operating system(s) to utilize or
which kernel to start, as well as to know where to install itself (for example, /dev/hda for the first
MBR of the IDE hard drive). A sample /etc/lilo.conf file looks like this:
Chapter 3:Boot Process, Init, and Shutdown
WARNING