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Re: restore boot block



Aarrgh, sorry, did that one from memory... If anyone is going to try this, then please use the updated values here: (Thanks Robert P. J. Day)

format of the MBR:

  446 bytes of code
  64 (4x16) bytes partition table
  2 byte signature (x55aa)


dd if=/dev/hda of=mypartitions skip=446 bs=64 count=1 dd if=/dev/zero of=/dev/hda bs=512 count=1 dd if=mypartitions of=/dev/hda skip=446

Sincerely,
Richard Black

- - - - - - - - - - - - - - - - - - - - - - - - -

The BOOT code is contained in the first 446 bytes.  Try wiping the first
446 instead of 512 and see if that does what you need.  You may also
need to clear the last 2 bytes of the 512 because it will contain 55aa
which is the boot code "signiture" which says the first 446 is valid.

dd if=/dev/hda of=mypartitions skip=446 bs=64 count=1
dd if=/dev/zero of=/dev/hda bs=512 count=1
dd if=mypartitions of=/dev/hda skip=446

# This isn't required if the new partitions are the exact same as the
old ones
echo w | fdisk /dev/hda

More info:
www.cpqlinux.com/mbr.html

Of course there are many other methods:

1. echo commands into fdisk
2. use sfdisk (scriptable fdisk)

3. Another method is to set PXE to first in the boot order, then have
the pxe server determine if they will do a local boot or do another
install.  This method is great for clusters and for testing.

Sincerely,
Richard Black

Fong Vang wrote:

>Currently, we automate the installation of hundreds of machines by wiping
>the bootblock (first 512 bytes of the disk) to force them to do PXE
boot on
>bootup. However, because parts of the partition table reside in this
>location as well, wiping the 512 bytes of the disk makes the partition
table
>unreadable. Once anaconda takes over (no longer booting), does anyone
know
>how one could restore the partition table. What would be the best
approach
>to recreate the partition table?
>
>
>
>
>
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