Thanks. When I asked the original question, I really didn't understand
how disk geometry and partitions and all worked. I've since dug into
lots of information on the subject and am fairly secure in it now. These
directions confirm what I'm currently attempting.
There is one bit of information that I still haven't squared away in my
head. I don't know of a good list to ask on, but perhaps since it is
related to this, someone here will know.
When the machine first boots, it runs the code in the MBR and uses the
parition table there to find the partitions on the machine. If there is
an extended partition, it will have another 512 byte boot sector at the
beginning with its own partition table. My question is about regular
partitions. When I create a file system in an image file (loopback
mounted), it seems to use the entire space, including the initial 512
bytes. When LILO or some other boot loader is installed into a partition
rather than the MBR, where does it put its code and how is it run? I
thought there would be an initial 512 bytes in regular partitions that
could be used for bootcode, but the filesystem seems to use it... Where
does LILO place itself when it is installed in a regular partition?
My goal is to get the Hurd booting under plex86. I'll report back any
progress I make.
--Ian
James McMechan wrote:
>
> Err, I don't think you have a "direct" geometry is the problem.
> your Grub is trying to load based on where the data was in partition 3 but
> your file does not have
> the unused space that partitions 1 and 2 used. Grub is trying to skip over
> to get to your kernel.
> To fix this you can use a sparse file created something like this
>
> use fdisk DEVICE2 to get CYCLINDERS/HEADS/SECTORS
> and PARTITION3's CYCLINDERSTART, CYCLINDEREND
>
> and then use dd to copy only the data you need
> Master boot record (MBR)
> dd if=DEVICE2 of=disk.img bs=512 count=1
> and then skipping all the other partitions
> dd if=DEVICE2 of=disk.img bs=$(( 512 * HEADS * SECTORS ))
> seek=CYCLINDERSTART \
> skip=CYCLINDERSTART count=$(( CYCLINDEREND-CYCLINDERSTART ))
>
> this will produce a spase file ( all unallocated cyclinders will read as
> zero and not take up space )
> which will have the same geometry as your real hard disk.
> This will show up in 'ls -l' as being the same size as your hard disk but
> 'df' will only show that sizeof(PARTITION3) is used
> |MBR|unallocated space|Boot sector Grub|Hurd
>
> ----- Original Message -----
> From: "Ian Duggan" <[EMAIL PROTECTED]>
> To: "plex86" <[EMAIL PROTECTED]>
> Sent: Friday, May 04, 2001 12:40 PM
> Subject: [plex86] Disk Image Layout
>
> >
> > Hi,
> >
> > I'm trying to create a bootable disk image for plex86 using another
> > partition that I have and am looking for assistance. I keep getting
> > drive geometry errors from GRUB, which I'm trying to use as a boot
> > loader.
> >
> > Here was the layout of the original partions
> >
> > DEVICE1: PARTITION1 (NTFS): Windows2k
> > DEVICE2: PARTITION1 (ext2): Linux
> > PARTITION2:(ext2): Hurd
> > PARTITION3:(swap): Swap (linux and hurd)
> >
> > I had LILO in the MBR of DEVICE1, which booted Win2k, or took you to the
> > boot sectors of D2P1 or D2P2. D2P1 had another LILO for booting various
> > Linux kernels in D2P1. D2P2 had GRUB for booting various Hurd/Gnumach
> > kernels in D2P2.
> >
> > So, I created an image of D2P2
> >
> > dd if=/dev/hdb2 of=disk.img
> >
> > So, I now have an image of D2P2 with Grub in it's boot sector, and
> > Hurd/Gnumach. Something like this:
> >
> > | Boot Sector Grub | Hurd |
> >
> > I think I need to create something like this:
> >
> > | MBR | Boot Sector Grub | Hurd |
> >
> > To try to boot it using plex86 and not have GRUB get the drive
> > geometries confused.
> >
> > Can someone point me to documentation on how I could lay out a proper
> > image file to boot with, or provide instructions on how to go about
> > creating it?
> >
> > --Ian
> >
> >
