Re: MBR Confusion
On Sat, Apr 07, 2007 at 01:30:57AM +0200, Matt Miller wrote:
> > I've attached an external hard drive to my etch AMD64 box, booted my
> > AMD64 box into the debian installer, and installed a fresh i386 etch
> > onto the external drive.
>
> Now I can't boot my box without the external drive attached, because
> grub complains with "error 21." I'm thinking that when the debian
> installer made the external drive bootable with my new i386 etch some
> stuff happened with the master boot record or something. Also, when I
> put the external drive into my Pentium III box, nothing happens.
> Apparently the right MBR stiff is not on there.
>
> Anyway, I'm in a bit deep at this point. Hopefully there is some simple
> way to prepare the external drive on my AMD64 box to be the internal,
> bootable drive of my Pentium III, and to tell grub on my AMD64 box that
> it doesn't need the external drive attached in order to boot.
>
> Go ahead and laugh. Just give me some good advice when you're done.
I'll only laugh 'cause you told me to.
Lets clarify:
AMD64 box has an internal hard drive with Etch installed on it.
Should have grub in the mbr, with menu.lst on the
internal hard drive.
AMD64 box also has external drive with Etch installed on it.
Should have grub in its mbr, with menu.lst on the
external hard drive.
With external box attached, can get grub on the external drive
and it boots to the external drive OK.
Without external box attached, grub complains Error 21. pinfo
grub says error 21 means:
Selected disk does not exist. This error is returned if
the device part of a device- or full file name refers to
a disk or BIOS device that is not present or not
recognized by the BIOS system.
So the bios has changed how it accesses drives since you installed on
the external drive.
What does your bios show?
Can you boot from within the grub command line (read the grub manual)?
Can you boot the install CD is rescue mode and reinstall grub?
All with the external drive uninstalled.
Then put that external drive into the target box and do similar
incantations to get grub to work there too.
Its _probably_ safe to assume that all your stuff is still on the
drives, its just a booting/grub problem. Print out your
/boot/grub/menu.lst file so you know what grub is supposed to be trying
to do (and so you have all the kernel params you need), then try
entering it manually.
When I use grub interactivly, I don't bother with grub's root( command,
I just preface each with the full path including device. With grub's
tab-completion this is pretty simple.
Good luck.
Doug.
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