Re-install bootstrap code(GRUB) in Redhat,Fedora,CentOS Linux

If you have repaired your system from a backup tape (by dump or tar), for example, you will need to repair the bootstrap area.You need to re-install the bootstrap code that is grub.

Please perform the following steps:

Boot from OS(Redhat,Fedora,CentOS) installation disc (for example, CD #1 or DVD).
Type “linux rescue” at the “boot:” prompt.
Mount all filesystems in read-write mode.
Change root to real root (‘/’) on your hard disk:
```
# chroot /mnt/sysimage
```
Re-install bootstrap code (GRUB).
- If you wish to re-install GRUB to the MBR on a SCSI or SATA disk (/dev/sda):
```
# grub-install /dev/sda
```
- If you wish to re-install GRUB to the PBR of Partition #2 on a SCSI or SATA disk (/dev/sda2):
```
# grub-install /dev/sda2
```
- If you wish to re-install GRUB to the MBR on an IDE disk (/dev/hda):
```
# grub-install /dev/hda
```
- If you wish to re-install GRUB to the MBR on a HP Smart Array disk (/dev/c0d0):
```
# grub-install /dev/cciss/c0d0
```