If GRUB was not installed during the installation process, it can be installed afterward. Once installed, it automatically becomes the default boot loader.
Before installing GRUB, make sure to use the latest GRUB package available or use the GRUB package from the installation CD-ROMs.
Once the GRUB package is installed, open a root shell prompt and run the command
is the location that the GRUB Stage 1 boot loader should be installed. For example, the following command installs GRUB to the MBR of the master IDE device on the primary IDE bus:
The next time the system boots, the GRUB graphical boot loader menu appears before the kernel loads into memory.
If GRUB is installed on a RAID 1 array, the system may become unbootable in the event of disk failure.