DragonFly users List (threaded) for 2012-07
Re: machine won't start
On Wed, Jul 4, 2012 at 8:16 PM, Carsten Mattner
> On Wed, Jul 4, 2012 at 8:11 PM, Carsten Mattner
> <email@example.com> wrote:
>> On Wed, Jul 4, 2012 at 8:07 PM, Matthew Dillon
>> <firstname.lastname@example.org> 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.