best fedora solution to securely erase folders/clean free space?

[Reindl Harald]

Am 30.03.2013 13:30, schrieb M. Fioretti:
> On Sat, Mar 30, 2013 13:10:57 PM +0100, Reindl Harald wrote:
>>
>> dd if/dev/urandom of=random.bin bs=16M; sync; rm -f random.bin
> 
> thanks.
> I assume there should be an equal sign after the "if", right?

ups - correct

> Anyway:
> 
> - shouldn't this be done several times, to make sure that whatever was
>   in the free space really is unrecoverable?

yes and no
yes in theory
no if you need not fear the CIA :-)

>> creates a file with random-stuff until the disk is full, syncs it
>> really to the disk and removes the file as the same with dd
>> if=/dev/zero will zerofill free space to make it possible shink thin
>> provisioned virtual-disks as example

if you have a virtual machine with growable disks and delete a lot of
data the disk will not get smaller, shrink the disk will not really work

after write zeros to the free space in the guest you can successful
shrink the virtual disk on the host system

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