HowTo Recreate Grub Install And The Master Boot Record (MBR) If Corrupted

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  • Problem: When booting NST from a hard disk install and you see the message: "Disk Error" (or something similar) on the screen after POST.
  • Solution: Typically, this is associated with a corrupt grub install and/or MBR on the hard disk. Use this HowTo to help recreate the grub install and MBR to help resolve this issue.


This HowTo shows the steps one can used to recreate a corrupt grub boot loader install and/or MBR on an NST system. Start by booting up "NST Live" (DVD or USB Flash Drive) or NST on a "USB Flash Drive" hard disk install. This example assumes the corrupt grub install and/or MBR is on the disk associated with device name: "/dev/sda" were partition: "/dev/sda1" is used for grub and the MBR is on "/dev/sda" sector 0.

  • 1) Make sure that there are no mounts using the "/boot" mount point:
[root@probe ~]# df
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/mapper/vg_probe-lv_root
                     235338552   4335136 228613664   2% /
/dev/sdb1               198337     22358    165739  12% /boot
tmpfs                  1419416         0   1419416   0% /dev/shm
[root@probe ~]#


  • 2) Unmount "/boot" if currently mounted:
[root@probe ~]# umount -v /boot
/dev/sdb1 umounted
[root@probe ~]#


  • 3) Mount "/boot" using partition: "/dev/sda1":
[root@probe ~]# mount -v /dev/sda1 /boot
mount: you didn't specify a filesystem type for /dev/sda1
       I will try type ext3
/dev/sda1 on /boot type ext3 (rw)
[root@probe ~]# df
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/mapper/vg_probe-lv_root
                     235338552   4335136 228613664   2% /
/dev/sda1               198337     22358    165739  12% /boot
tmpfs                  1419416         0   1419416   0% /dev/shm
[root@probe ~]#


  • 4) Reinstall grub and the MBR on the hard disk (/dev/sda):
[root@probe ~]# grub-install --root-directory=/ /dev/sda
Installation finished. No error reported.
This is the contents of the device map //boot/grub/device.map.
Check if this is correct or not. If any of the lines is incorrect,
fix it and re-run the script `grub-install'.

# this device map was generated by anaconda
(hd0)     /dev/sda
[root@probe ~]#

One can review the " Backup And Restore The MBR" HowTo document as an alternative method for resolving this issue.