[Gllug] Wiping free space.

JLMS jjllmmss at googlemail.com
Tue Dec 29 10:30:34 UTC 2009

On Mon, Dec 28, 2009 at 4:27 PM, general_email at technicalbloke.com
<general_email at technicalbloke.com> wrote:
> I was wondering how one would go about overwriting empty space on a
> standard ext3 partition. The quickest naive solution would seem to be to
> pipe the output of /dev/random to a file until all the disk space is
> used then delete it but...
> a) I've heard bad things may happen if the system disk get completely
> full on unix systems, and...

It depends.

If you do something like that in your / filesystem, then yes, you will
see all kind of weird behaviour.

If you do that anywhere else, most likely it would only affect
applications writing there, so just stop any applications using that
filesystem prior to do what you suggest.

> b) AFAIK, files are block aligned so files which don't divide perfectly
> into the block size may have space at the very end of that the OS
> doesn't regard as free.
> Are the above conerns legitimate or just here-say? If the former are
> there any apps I would find in the big 3 repos that overwrite unused
> space while mitigating the above?

My main concern would be why to do all this at all.

If the data is so sensitive then backup your file systems, clean the
disk properly (using DBAN or something similar) or destroy it (if it
is old you can get a cheap replacement easily, if it is new, it will
cost you relatively little to get a newer, bigger disk), and recover
your system from the backups.
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