How do I install GRUB to the MBR?

Introduction

This exercise will show you how to install GRUB to the MBR assuming that the GRUB software is installed on your computer. If GRUB is not on your computer for some reason (rpm -q grub), then you will need to install the appropriate RPM for GRUB. However, be aware that GRUB is included in the default RHEL install. If you need to install the GRUB rpm, this could be a sign of bigger problems.


Procedure

1) Our boot partition is /dev/sda1. We want to install GRUB to the master boot record of /dev/sda. This is because our BIOS passes control to /dev/sda once it has done its work. In order to do this, we need to first determine the GRUB device name for /dev/sda by looking in /boot/grub/device.map:
(fd0) /dev/fd0
(hd0) /dev/sda
(hd1) /dev/sdb

We can tell that our GRUB device is (hd0).

2) We now need to enter the GRUB shell. To do this, we simply type grub while logged in as root:
[root@station1 ~]# grub
Probing devices to guess BIOS drives. This may take a long time.

3) After we are presented with a GRUB prompt (grub> ), we will need to specify where the boot partition is with the following command:
grub> root (hd0,0)

Notice how we used (hd0,0). In GRUB language, this identifies /dev/sda1.

4) We now need to tell GRUB which disk’s master boot record it needs to install to. This is done by typing the following command:
grub> setup (hd0)

This says that we want GRUB to install to the master boot record of /dev/sda.

5) To get out of the GRUB shell, we simply type:
grub> quit

6) At this point, GRUB is now installed on /dev/sda and knows that the boot partition is /dev/sda1. It is safe to reboot.