Re: Removing bootstrap data on i386

[George Michaelson <ggm%pobox.com@localhost>]

On 17/12/2009, at 10:14 AM, George Michaelson wrote:

> 
> On 17/12/2009, at 10:07 AM, Dave B wrote:
> 
>> On Wed, Dec 16, 2009 at 11:55:52PM +0000, George Michaelson wrote:
>>> Its simpler than this
>>> 
>>> dd if=/dev/zero of=/dev/rwd0d bs=512 count=1
>> 
>> Does that preserve partition info?
> 
> 
> nope. if you need to preserve the partition info, you have to blank less than 
> 512.
> 
> its the first 446 bytes
> 
> so dd if=/dev/zero of=/dev/rwd0d bs=446 count=1
> 
> http://en.wikipedia.org/wiki/Master_boot_record

...And if you want to be ultra-paranoid, avoid wiping the 'disk signature' 
which is 440-446, ie ONLY wipe the first 440 bytes. I don't think *BSD cares 
about it, and its repareable, but some other OS (Windows, Linux) do use it.

dd if=/dev/zero of=/dev/rwd0d bs=440 count=1

you can also back the sucker up before you wipe, so you can restore it

dd if=/dev/rwd0d of=/some/other/disk/path/mbr.bin bs=512 count=1

so you can replace it. (for 512 you could use 440, 446 ...)

-George