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

[Bruno Wolff III]

On Sat, Mar 30, 2013 at 12:58:31 +0100,
   "M. Fioretti" <mfioretti at nexaima.net> wrote:
>Greatings,
>
>I started reading online to refresh what I knew about secure deletion
>of files, and being sure that "free space" on an ext3/ext4 partition is
>surely "free", that is you can't recover the files that _were_ there.

There are issues that may or may not apply to you depending on what you are 
really worried about (your threat model). Note for example that disk drives 
have spare sectors that may have been used for some of your data that you 
can't directly access. (Though the secure erase function of your disk drive 
is supposed to erase these sectors as well as the rest of the disk.) If 
you have a flash based device there is lots of space that you don't have 
direct access to and gets used regularly (unlike spare sectors on disk 
drives).

It makes a difference if you are concerned about attacks by users of the 
machine, people who grab the machine while it is powered on or people who 
grab it while powered off.

The latter case can be handled well by using encrypted partitions.

If you are worried only about files that used to exist, but don't going 
forward you may want to consider backing up just the files you want, 
overwriting the whole disk(s) with something (zeros should be fine) using dd,
then invoke the secure erase function of the disk(s). Then reinstall and 
restore from backup.