machine won't start

[Carsten Mattner]

On Wed, Jul 4, 2012 at 8:16 PM, Carsten Mattner
<carstenmattner at gmail.com> wrote:
> On Wed, Jul 4, 2012 at 8:11 PM, Carsten Mattner
> <carstenmattner at gmail.com> wrote:
>> On Wed, Jul 4, 2012 at 8:07 PM, Matthew Dillon
>> <dillon at apollo.backplane.com> wrote:
>>>
>>> :Thanks Matt for the explanation and tip.
>>> :
>>> :It did of course hang when I tried to DEL into the BIOS.
>>> :What worked is pulling out the sata connector, entering
>>> :the BIOS putting it back and then detecting the disk.
>>> :Interesting the auto detection then worked. I've explicitly
>>> :set it to LARGE and now I can boot a rescue cd.
>>> :
>>> :How many bytes should I zero out for the disk to be
>>> :"normal" again? 512bytes? 4megs?
>>>
>>>     The BIOS is basically just accessing the slice table in the first
>>>     512 bytes of the disk.  If I want to completely wipe a non-GPT
>>>     formatted disk I usually zero-out (with dd) the first ~32MB or so
>>>     to catch both the slice table and the stage-2 boot and the disklabel
>>>     and the likely filesystem header.
>>>
>>>     Destroying a GPT disk requires (to be safe) zero'ing out both the first
>>>     AND the last X bytes of the physical media to also ensure that the
>>>     backup GPT table is also scrapped.  Again, to be safe I zero-out around
>>>     32MB at the beginning and 32MB at the end w/dd (if it's GPT).
>>
>> How do I tell dd to delete x bytes at the end of device? Negative values?
>
> Will try seek=nG

dd's seek= operates on blocks so have to supply multiple of bs=.

Thanks again Matt and everybody.