wipe utility

[peterman at eecs.tufts.edu (Charles Peterman)]

Not useful for wiping individual files, but great for getting drives 
prepped for destruction or cleaning freespace before retasking a 
machine, I use dd.


1. Find out how much space is available on the partition, using a 
magical incantation of df and awk.  Call the result FOO.
2. Add some % of that depending on file system.  Most file systems can 
go over a 100% as reported by df. Store result in FOO.
3. For some magical number of iterations, I found that seven was 
sufficient for preventing
     a less than recent version of a popular disk forensics package from 
finding anything, write   	over the space.
	dd if=/dev/random of=/partition/filefoo bs=1m count=FOO/bs

The absolute size of filefoo is limited by the OS, use multiple files 
if needed. If don't have the time for /dev/random, using a really large 
memory mapped file (install ISO images work well) to be faster.  Use a 
random iseek value for dd.   Of course, in that case, you need more 
individual invocations of dd and you need to check df after each run.

Hope this qualifies as Useful Information (TM).

Charles

On Aug 13, 2004, at 10:04 AM, Cole Tuininga wrote:

On Fri, 2004-08-13 at 10:01, Eric wrote:
>
> What would be a good way to wipe something on a journaling filesystem?

What you would need is a utility that had direct access to the hard
drive, bypassing the filesystem layer.  It would also need to understand
the setup of the filesystem though.

If the filesystem in question is ext3, there's a slightly simpler
method.  Unmount it, and remount it as ext2.  For the most part, this
should work and will simply turn off the journaling.  At that point, a
utility such as wipe would work just fine.  After you're done, unmount
the filesystem and remount it once again as ext3.

-- 
Computers are like air conditioners:
They stop working properly when you open windows.

Cole Tuininga
Lead Developer
Code Energy, Inc
colet at code-energy.com
PGP Key ID: 0x43E5755D


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Charles Peterman
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