Unusual Question

[Warren Block]

On Fri, 14 Jul 2017, Arthur Chance wrote:

> On 14/07/2017 07:11, Doug Hardie wrote:
>>
>>> On 13 July 2017, at 21:44, David Christensen <dpchrist at holgerdanske.com> wrote:
>>>
>>> On 07/09/17 02:57, Doug Hardie wrote:
>>>> I have a FreeBSD 9.3 remote server that needs to be purged.  I know that rm -rf / will remove all the directory entries, but I need to write over the drive.  I thought that dd if=/dev/zero of=/dev/ada0 might do the trick, but it gives an not permitted error.  The whole thing can crash and burn at the end.  This is an unmanned site so moving drives is not viable.
>>>
>>> If the machine has BIOS and the system drive isn't too large, write an assembly program that fits into the MBR bootstrap code area to wipe the rest of the drive, assemble the program, write it into the MBR, and reboot.
>>>
>>>
>>> Bonus: the program deletes the MBR when done wiping the rest of the drive.
>>
>> Neat idea, but I have a number of these systems and they all use different disk drives.  That would be a lot of work writing drivers for each type.
>
> How about using the BIOS extended write sector call (INT 13h, AH=43h) in
> your code? That should be portable.

Won't that choke after 2TB?  It might wrap around to the start of the 
drive after the 2TB mark, or just fail.  Failure would be better, at 
least it would mean that half of a 4TB drive might be left intact 
without notice.

But this idea of having a self-destructive boot block has some other 
problems.  A tiny space for code, a dangerous thing to have lying 
around, and if you have to reboot into it, might as well reboot into 
mfsBSD (http://mfsbsd.vx.sk/) and be sure that it works.

For SSDs, the Secure Erase option might be viable.  I have not yet had 
that work in the couple of times I've tried it, but that could be due to 
improper usage or possibly lack of support on the old SSDs being used.