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Re: changing the MBR for a dual-bootup system

On Tue, 2006-10-17 at 06:48 +0200, jdkaye10@yahoo.es wrote:
> Andreas Glaeser wrote:
> > On Sun, 2006-10-15 at 18:17 +0200, jdkaye10@yahoo.es wrote:
> >> Hi all,
> >> I am running Debian Etch 2.6.15-1-686 on an Asus motherboard with an
> >> AMD64 chip. Etch is running on /dev/hda. I wanted to try out the 64bit
> >> kernel so I installed a second HD /dev/hdb and installed Sid amd64 from
> >> scratch. I didn't want to get involved in chroot type stuff which is why
> >> I did it this way. Both systems use grub but the MBR is pointing to
> >> /dev/hdb for the menu.1st file. When I upgraded the kernel on the Etch
> >> 686 system of course I had to copy the newly created menu.1st item from
> >> Etch to the menu.1st file on Sid amd64 in order for it to show up on the
> >> grub menu on bootup. That was ok for a while but now I'm getting disk
> >> errors on /dev/hdb. I can still boot into Etch ok but I would like to
> >> change things so that the MBR looks at /dev/hda instead of /dev/hdb. I
> >> may have to replace the hdb drive if reformatting and reinstalling Sid
> >> amd64 don't clear up the problems.
> >> 
> >> Can someone tell me how to tell grub to ignore /dev/hdb and look at
> >> /dev/hda for the bootup menu?
> >> Thanks in advance for any advice.
> >> Jonathan
> >> 
> > Maybe ´grub-install --root-directory=/dev/hda /dev/hda´ has the desired
> > effect.
> > 
> > 
> > Regards
> Thanks for that Andreas,
> I'll give it a try and let you know if it works. I also created a grub boot
> disk with stage2_eltorito on it. Would it be better to try it from there?
> Cheers,
> Jonathan
Dear Jonathan,
as long as your System is still running and booting correctly there is
probably no need to use a live CD for reinstalling Grub . But it is
safer to make a backup of the MBR before giving it a try:
dd if=/dev/hda of=/boot/mbr.hda bs=512 count=1
So if anything goes wrong it can be restored with something like:
dd if=/mnt/hdax/boot/mbr.hda of=/dev/hda bs=512 count=1
I think an existing menu.lst -file is not touched by ´grub-install´.
You can make a copy of menu.lst, too, or copy that from hdb in case.

Yours sincerely
Andreas Glaeser <aglaeser@arcor.de>

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