2010/7/18 Girish Venkatachalam <[email protected]>

>
> >    You have a file "secret".  The following makes it so no one
> >    can read it.  If the file was 12 bytes, it's now 4096 after it
> >    has been over written 100 times.  There's no way to recover this.
>

Shred is not completely effective on log-structured and journaled file
systems. e.g. ext3 and ReiserFS

Not effective on RAID, Snapshot based file systems, ZFS, BTRFS etc..

Not effective on Cache based systems and applications that create a "temp
file" e.g. open office.

Not effective on Compressed file systems.

>    It can be applied to a device
>
>
>
>      $ shred -n 100 -z -u /dev/fd0
>

using the dd command is best to destroy data on a device.

e.g.  $ dd if=/dev/urandom of=/dev/fd0 bs=4K count=5

if ==> input file [ see below ]
of ==> output file [ your device ]

input file can be a random data file /dev/random or /dev/urandom or zero
file /dev/zero

HTH
Yogesh.
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