grub/mbr/not primary hd

Oskar von dem Hagen · External Since: Nov 28, 2006 Posts: 3

Hi,
my computer/bios allows me to boot from different IDE/SATA disks.
Currently I have three:
hd0 boots XP
hd1 is supposed to boot grub/ubuntu (but doesn't work yet)
hd2 boots W2K

Grub is installed in the MBR of hd1. But when I boot from hd1 I only get
something like
"GRUB GRUB GRUB GRUB GRUB"
and then nothing.

I have been able to install GRUB on another (linux only) computer in such
a way that grub allows me to edit the boot disk (on that computer an
update always writes the primary ide harddisk into the boot menu but the
system is on an scsi disk) but on this computer I didn't succeed.

Is there information available about the part of GRUB that is in the MBR?
There is apparently a problem with the numbering of the harddisks. Where
in the MBR is the information about the harddisk/partition to look for the
menu?

Oskar

Jan van Wijk · External Since: Jun 21, 2007 Posts: 4

On Thu, 2 Aug 2007 13:21:11 UTC, "Oskar von dem Hagen" <garbage RemoveThis @vondemhagen.de> wrote:
Hi Oskar

<snip>
> Is there information available about the part of GRUB that is in the MBR?
> There is apparently a problem with the numbering of the harddisks. Where
> in the MBR is the information about the harddisk/partition to look for the
> menu?

Sure, check the sources Smile

By coincidence, I did just that a few days ago, since I was
writing GRUB analysis and display code for a disk tool.

The disk-number itself, is a single-byte at offset 0x40 in the MBR,
0x80 is first disk, but it often has the value 0xff, meaning to take
whatever the BIOS value is for 'this' disk.

The physical-sector-number (PSN) for the start of stage-1.5
or stag-2 (depending on situation) is stored as a 4 byte value
(ULONG) at offset 0x44.

There is some other stuff in the same area, but that is relevant for
loading these stages into memory, not the on-disk location.

Regards, JvW

--
Jan van Wijk; Author of DFSee: http://www.dfsee.com

Oskar von dem Hagen · External Since: Nov 28, 2006 Posts: 3

Hi Jan,
>
> Sure, check the sources Smile

>
Right. Still have to get used to having source files available.

> The disk-number itself, is a single-byte at offset 0x40 in the MBR,
> 0x80 is first disk, but it often has the value 0xff, meaning to take
> whatever the BIOS value is for 'this' disk.
Replaced 81 by 82 and got the first decent error message.

Thanks, will battle on.
Oskar

Jan van Wijk · External Since: Jun 21, 2007 Posts: 4

On Fri, 3 Aug 2007 01:05:28 UTC, "Oskar von dem Hagen" <garbage DeleteThis @vondemhagen.de> wrote:
Hi Oskar,

> > Sure, check the sources Smile

> >
> Right. Still have to get used to having source files available.

Smile

> > The disk-number itself, is a single-byte at offset 0x40 in the MBR,
> > 0x80 is first disk, but it often has the value 0xff, meaning to take
> > whatever the BIOS value is for 'this' disk.
> Replaced 81 by 82 and got the first decent error message.

OK, good.

> Thanks, will battle on.

You may want to take a look at my DFSee disk-tool as well,
there is a full-function BETA available at:

http://www.dfsee.com/download/dfsee9bb.zip
or
http://www.dfsee.com/download/dfsee9xx_linux.tgz

The ZIP has DOS, Windows, OS/2 and Linux versions.

You can use that to browse your partition tables, including
GRUB details, and it also includes a binary sector editor.
(and soon a disassembler for the hackers amongst us Smile

Regards, JvW

--
Jan van Wijk; Author of DFSee: http://www.dfsee.com