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## Auto-converted by kwiki2moinmoin v2005-10-07
= Recover Grub =
Imagine for any reason you have any other crapy OS installed next to Debian. And for any reason you need to reinstall it because is really broken. Again, imagine this crappy OS has a crappy installation and overwrites the disk MBR to own the full computer. What's next? reinstall Debian? no
## page was renamed from GrubRecover
#language en
~-[[DebianWi
ki/EditorGuide#translation|Translation(s)]]: English - [[fr/GrubRecover|Français]] - [[it/GrubRecover|Italiano]] - [[ru/GrubRecover|Russian]]-~
----

= Recover GRUB =
Imagine for any reason you have any other OS installed next to Debian. And for any reason you need to reinstall it because is really broken. Again, imagine that OS has a crappy installation and overwrites the disk MBR or GPT to own the full computer. What's next? Reinstall Debian? No.
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To recover grub you need a console from a live CD. For example, boot with Debian installation CD and hit crtl+alt+F2. Knoppix makes the work too. Then mount the Debian '' in the hard disk, change the mount point to be the new '' and exec grub-install. In any case, you can use [[http://www.supergrubdisk.org/|SuperGRUB]], a boot utility that can restore and repair overwritten and misconfigured GRUB installs or directly boot various operating systems.
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May be these commands clarify the steps. For this example, Debian is in /dev/hda2 == Standard procedure ==
The Debian Installer (DVD, netinst CD, floppy, netboot, etc.) can be used to rescue systems, for example if they fail to boot after an upgrade. You should '''read and follow the instruction''' "Recovering a Broken System" section of the Installation Guide<<FootNote(http://www.debian.org/releases/)>> (look for it in the index) [link to [[http://www.debian.org/releases/stable/i386/ch08s07.html|stable/i386]]].

=== Troubleshooting : 'grub-install /dev/sda' failed. ===
If D-I's "Reinstall GRUB boot loader" option fails, with error message
'''{{{
Unable to install GRUB in /dev/sda
Executing 'grub-install /dev/sda' failed.
This is a fatal error.
}}}'''
Also, the d-i log console (Alt-F4) displays {{{
grub-installer: /dev/scsi/host0/bus0/target0/lun0/disc does not have any corresponding BIOS Drive
}}}
You can still use the following method to reinstall GRUB.
Choose "Execute a shell in ''Your root partition''" in the d-i rescue menu.

'''Locate your root partition''' :
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 # mkdir /my-debian
 # mount /dev/hda2 /my-debian
 # chroot /my-debian
 # grub-install /dev/hda
 # exit
 # umount /my-debian
 # reboot
fdisk -l

Disk /dev/sda: 39.9 GB, 39996820992 bytes
255 heads, 63 sectors/track, 4862 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

   Device Boot Start End Blocks Id System
/dev/sda1 * 1 111 891576 7 HPFS/NTFS
/dev/sda2 167 230 514080 82 Linux swap
/dev/sda3 231 784 4450005 83 Linux
/dev/sda4 785 4862 32756535 f W95 Ext'd (LBA)
/dev/sda5 785 4862 32756503+ 83 Linux
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'''Reinstall GRUB bootloader ''' ~-([[http://www.gnu.org/software/grub/manual/grub.html#Installation-under-UNIX|grub manual]])-~
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May be you need to load the fs module manually before mounting, for example If you have grub-legacy <<FootNote(If you have stage1, stage2 and menu.lst files in /boot/grub/ then you probably have a working grub-legacy. If you have several *.mod files and a grub.cfg file in /boot/grub/ then you have the new grub.)>> and your root partition is /dev/sda3 then you can re-install grub in the MBR of your hard drive by typing the following commands :
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 # modprobe reiserfs sudo grub
grub>root (hd0,2)
grub>setup (hd0)
grub>quit
exit
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Note that in grub-legacy (hd0,2) is the third partition.
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That's all. No more, no less. Then choose "Reboot the system", everything should be fine.

----
CategoryBootProcess

Translation(s): English - Français - Italiano - Russian


Recover GRUB

Imagine for any reason you have any other OS installed next to Debian. And for any reason you need to reinstall it because is really broken. Again, imagine that OS has a crappy installation and overwrites the disk MBR or GPT to own the full computer. What's next? Reinstall Debian? No.

In any case, you can use SuperGRUB, a boot utility that can restore and repair overwritten and misconfigured GRUB installs or directly boot various operating systems.

Standard procedure

The Debian Installer (DVD, netinst CD, floppy, netboot, etc.) can be used to rescue systems, for example if they fail to boot after an upgrade. You should read and follow the instruction "Recovering a Broken System" section of the Installation Guide1 (look for it in the index) [link to stable/i386].

Troubleshooting : 'grub-install /dev/sda' failed.

If D-I's "Reinstall GRUB boot loader" option fails, with error message

Unable to install GRUB in /dev/sda
Executing 'grub-install /dev/sda' failed.
This is a fatal error.

Also, the d-i log console (Alt-F4) displays

grub-installer: /dev/scsi/host0/bus0/target0/lun0/disc does not have any corresponding BIOS Drive

You can still use the following method to reinstall GRUB. Choose "Execute a shell in Your root partition" in the d-i rescue menu.

Locate your root partition :

fdisk -l

Disk /dev/sda: 39.9 GB, 39996820992 bytes
255 heads, 63 sectors/track, 4862 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1         111      891576    7  HPFS/NTFS
/dev/sda2             167         230      514080   82  Linux swap
/dev/sda3             231         784     4450005   83  Linux
/dev/sda4             785        4862    32756535    f  W95 Ext'd (LBA)
/dev/sda5             785        4862    32756503+  83  Linux

Reinstall GRUB bootloader (grub manual)

If you have grub-legacy 2 and your root partition is /dev/sda3 then you can re-install grub in the MBR of your hard drive by typing the following commands :

sudo grub
grub>root (hd0,2)
grub>setup (hd0)
grub>quit
exit

Note that in grub-legacy (hd0,2) is the third partition.

Then choose "Reboot the system", everything should be fine.


CategoryBootProcess

  1. http://www.debian.org/releases/ (1)

  2. If you have stage1, stage2 and menu.lst files in /boot/grub/ then you probably have a working grub-legacy. If you have several *.mod files and a grub.cfg file in /boot/grub/ then you have the new grub. (2)