machine won't start

[Carsten Mattner]

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