[plug] HDD Erasure

[Stuart Midgley]

You need to be really careful using /dev/urandom like this.  The  
kernel uses all sorts of inputs to generate these random numbers and  
you can "run out".  Especially if you set the system going erasing  
and then go away for a coffee/dinner etc.  Without keyboard/mouse/ 
network activity your numbers can become very un-random and the call  
can even block waiting on more input events).

I would strongly suggest using a downloaded package which tend to  
have random number generates built in.  These use a few inputs (/dev/ 
urandom time of day etc) to generate an unknown seed and should be  
good for a large number of random numbers.  Google is your friend here.

If your going to use dd to erase a disk, you should use a larger  
block size to make it go faster

	dd if=/dev/zero of=/dev/hda bs=8192k

Stu.


On 13/11/2005, at 0:25, Jonathan Young wrote:

> You can also try:
>
> dd if=/dev/urandom of=/dev/hda
>
> and let it run until the end of the disk is reached.  It may take a  
> few hours. Once it completes, repeat it again as many times as you  
> feel you want to.
>
> You could also alternate to
>
> dd if=/dev/zero of=/dev/hda
>
> This will do a zero fill.
>
> I would personally recommend 3 to 7 wipes with random stuff as I  
> have used and tested (tried to recover data) using this method and  
> was pleased with the results under the exact same cirumstances  
> (handing corporate laptops to ex-staff as leaving presents!).
>
> Can see any problem with either of these commands doing exactly  
> what you want.  But it's real late at night, so include in there  
> the usual disclaimer... RTFM, ensure /dev/hda IS the drive you want  
> to wipe etc. etc.
>
> I suspect you would need root access for this kind of operation  
> too, though I doubt you would be doing it as anything else.
>
> - Jonathan.


--
Dr Stuart Midgley
Industry Uptake Program Leader
iVEC, 'The hub of advanced computing in Western Australia'
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Australia

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