[Lancaster] Re: Wiping hard drives

[Andy Baxter]

On Thursday 06 May 2004 09:08, Ken Hough wrote:
> Andy,
>
> Thanks. I've got a copy of Tom's Root Boot Disk and so will try.
>
> I take it that the procedure writes stuff to ramdomly selected parts of
> a drive, rather than writing zeros to all parts.

/dev/random is a pseudo-device, which returns a string of (pseudo, but 2 
pseudos in the same sentence is confusing...) random numbers when it's read. 
I.e. when you read from it, the kernel just generates a series of random 
numbers and it looks like there's a real device with those numbers on it. 
There's another pseudo-device called /dev/zero which returns just 
zeros. /dev/hda is the raw device file for the first hard disk before you put 
any partition information or filesystem on it, so if you copy /dev/random to 
this using 'cat', it should fill the whole drive with random bytes.

The reason for doing it several times is that even when a drive has been 
rewritten, the previous data can still sometimes be read as a magnetic 'ghost 
image' of the old data (but only by using specialist equipment on the 
disassembled drive platters), especially if you wipe it by filling with 
zeros.

it might be better though to use the 'dd' command rather than cat, which is 
more meant for things like this. e.g.

dd if=/dev/random of=/dev/hda bs=512

hope this helps,

andy.

>
> Regards
>
> Ken Hough
>
> Andy Baxter wrote:
> > On 2004.05.05 20:02, Tim Churchill wrote:
> >> I could send Ken (email) a copy of Killdisk - it writes zeros to any
> >> hard drive, boots from the floppy (DOS), and is only 649Kb. I'd do it
> >> myself, but am snowed under with work at present, and the PCs will
> >> need physically cleaning out - they have the dust of ages in them so
> >> want stripping down and re-assembling.
> >
> > Or else get a copy of tom's root boot disk from: http://www.toms.net/
> > rb/, boot from floppy using this, and then do cat /dev/random > /dev/
> > hdx a few times? (where hdx is the relevant disk device - e.g. hda,
> > hdb, hdc, hdd)
> >
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Thanks, andy.