Install the bootloader

In order for the target system to boot, the bootloader must be installed on the Master Boot Record of one of your hard drives.

This process differs based on the version of GRUB your distribution uses. To determine which version you have, run rpm --root=/mnt/root -q grub. If there is output, you have GRUB 1; if there is no output you have GRUB 2.

GRUB 1

Write grub.conf

You will need to write a grub.conf to instruct GRUB where to boot from.

1. Determine the version of the kernel package you are running:

   rpm --root=/mnt/root -q kernel --qf '%{VERSION}-%{RELEASE}.%{ARCH}\n'
   

   This command will output something similar to 2.6.32-220.4.1.el6.x86_64.

2. Determine the UUID of the root partition (the partition mounted at /mnt/root). Your fstab should contain this.

Write this to /mnt/root/boot/grub/grub.conf:

default=0
timeout=5
title Scientific Linux (UNAME)
    root (hd0,0)
    kernel /vmlinuz-UNAME ro root=UUID=ROOT_UUID selinux=0
    initrd /initramfs-UNAME.img

replacing UNAME with the kernel version and ROOT_UUID with the UUID of the root partition.

grub-install

Determine the hard drive (not the partition) that will be booted from. (In most cases, this is the only hard drive.) Run grub-install:

grub-install --root-directory=/mnt/root /dev/sdX

GRUB 2

1. Mount the special filesystems under /mnt/root:

   mount -t devtmpfs devtmpfs /mnt/root/dev
   mount -t proc proc /mnt/root/proc
   mount -t sysfs sysfs /mnt/root/sys
   

2. Enter a chroot under /mnt/root:

   chroot /mnt/root
   

3. Determine the hard drive (not the partition) that will be booted from. (In most cases, this is the only hard drive.)

4. Run these commands inside the chroot:

   grub2-install /dev/sdX
   grub2-mkconfig -o /boot/grub2/grub.cfg
   

5. Exit the chroot by typing exit or pressing Control-D.

6. Unmount the special filesystems under /mnt/root:

   umount /mnt/root/dev
   umount /mnt/root/proc
   umount /mnt/root/sys