Reinstall GRUB?

[Todd Denniston]

Doctor Who wrote, On 01/25/2008 03:10 PM:
> 2008/1/25 Mikkel L. Ellertson <mikkel at infinity-ltd.com>:
>> Doctor Who wrote:
>>> I recently added another hard drive to my machine.  Previously, I had
>>> 2 hard drives and Fedora was installed on one along with Vista.  I
>>> installed grub to Fedora''s root and used a 3rd party boot loader to
>>> access Fedora and other distros.
>>>
>>> Now that the 3rd SATA drive is installed, Fedora's grub is messed up
>>> because it's not on the drive it thinks it is (different order to
>>> drives now).  How can I go about 'fixing' Fedora's grub entry and
>>> re-installing grub to Fedora's root partition (not the MBR)?
>>>
>>> Thanks.
>>>
>> Probably the easiest way to to boot the rescue CD or the install
>> DVD/CD in the rescue mode, and have it mount your partitions. Then
>> edit your Grub configuration and run grub-install. (I am guessing
>> that you can not get to the Grub prompt because Grub is looking for
>> stage 1.5 in on the wrong drive.) If you are not using partition
>> labels, you will also have to edit /etc/fstab.
>>
>> For editing, and re-installing Grub, I like to chroot to the mount
>> point for the root file system. But if you are not using partition
>> labels, the rescue mode will have problems mounting /boot and
>> possible other partitions because the information in /etc/fstab will
>> point to the wrong drive. In that case, you will end up having to
>> mount at least some of the partitions by hand before you can fix things.
>>
>> I don't know your level of acknowledge, so ask about the steps you
>> need detailed explanations of. (or search the list) The different
>> steps have been covered more then once, but it isn't always easy to
>> find them.
>>
>> Mikkel
> 
> I can boot into Fedora via grub from another Linux install.  I assume
> that will make things easier (making the edits from within Fedora
> itself).  Can someone outline the steps to find out what the grub (and
> fstab??) entries *should* be and the best (read Fedora-way) to change
> them?
> 
> Thanks.
> 

IIRC current Fedora's use labels in the fstab, so you should not need to mess 
about there.

If you are booting from the same grub, into another Linux, then you should be 
able to just edit grub.conf and change the 'root (hdx,y)' line, where the x 
refers to the hard drive[0 indexed] and y the partition.
If you can print, it may be a good idea to print your grub.conf before you 
change anything. by printing it, if the changes make it so you can't get back 
to the fedora you can get now, you should be able to enter the grub command 
line and enter the data from the printout and get back in. Backup plans are 
good. 8)


<about to get in just over my ears>
not sure if you need to be working with
/boot/grub/device.map
I would suggest trying the grub.conf changes first.
If you do, then grub-install has a --recheck among it's options. You might 
want to make a backup of the current map first though.

if/when Mikkel comes back, you can probably trust him more than me.

-- 
Todd Denniston
Crane Division, Naval Surface Warfare Center (NSWC Crane)
Harnessing the Power of Technology for the Warfighter