Boot loading can be a complex area, so a few cautionary words are in order. Be familiar with the current boot loader and any other operating systems present on the hard drive(s) that need to be bootable. Make sure that an emergency boot disk is ready to “rescue” the computer if the computer becomes unusable (un-bootable).

Earlier, we compiled and installed the GRUB boot loader software in preparation for this step. The procedure involves writing some special GRUB files to specific locations on the hard drive. We highly recommend creating a GRUB boot floppy diskette as a backup. Insert a blank floppy diskette and run the following commands:

dd if=${CLFS}/boot/grub/stage1 of=/dev/fd0 bs=512 count=1
dd if=${CLFS}/boot/grub/stage2 of=/dev/fd0 bs=512 seek=1

Remove the diskette and store it somewhere safe. Now, run the grub shell:

grub

GRUB uses its own naming structure for drives and partitions in the form of (hdn,m), where n is the hard drive number and m is the partition number, both starting from zero. For example, partition hda1 is (hd0,0) to GRUB and hdb3 is (hd1,2). In contrast to Linux, GRUB does not consider CD-ROM drives to be hard drives. For example, if using a CD on hdb and a second hard drive on hdc, that second hard drive would still be (hd1).

Using the above information, determine the appropriate designator for the root partition (or boot partition, if a separate one is used). For the following example, it is assumed that the root (or separate boot) partition is hda4.

Tell GRUB where to search for its stage{1,2} files. The Tab key can be used everywhere to make GRUB show the alternatives:

root (hd0,3)

Tell GRUB to install itself into the MBR of hda:

setup (hd0)

If all went well, GRUB will have reported finding its files in /boot/grub. That's all there is to it. Quit the grub shell:

quit

Create a “menu list” file defining GRUB's boot menu:

cat > ${CLFS}/boot/grub/menu.lst << "EOF"
# Begin /boot/grub/menu.lst

# By default boot the first menu entry.
default 0

# Allow 30 seconds before booting the default.
timeout 30

# Use prettier colors.
color green/black light-green/black

# The first entry is for CLFS.
title CLFS 1.0.0rc5
root (hd0,3)
kernel /boot/clfskernel-2.6.17.13 root=/dev/hda4
EOF

Add an entry for the host distribution if desired. It might look like this:

cat >> ${CLFS}/boot/grub/menu.lst << "EOF"
title Red Hat
root (hd0,2)
kernel /boot/kernel-2.6.5 root=/dev/hda3
initrd /boot/initrd-2.6.5
EOF