[Gllug] Wiping free space.

[general_email at technicalbloke.com]

James Courtier-Dutton wrote:
> 2009/12/28 general_email at technicalbloke.com <general_email at technicalbloke.com>:
>   
>> 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...
>>
>> 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?
>>
>>
>> Roger.
>> --
>>     
>
> Roger,
>
> I don't know exactly why you would want to do this.
> If it is because the data is private and you want to properly delete
> it then another approach would be better.
> I would recommend encrypting with LUKS or some other tool the entire
> partition and store your private data there.
> Then, even if the HD crashes, you can still be sure that your private
> data is safe.
>
> There are other reasons why one might wish to write zeros, for
> example, in order to compress an entire HD backup.
>
> Kind Regards
>
> James
>   

Well there's a venerable windows file shredder program called 'eraser'
which has an option to shred empty space, I was wondering if there was
an equivalent in linux. There's not many use cases for it really but
there are some...

I do domestic & SOHO tech support for a living and often when I have
installed a new machine for someone they ask me how they should make
sure their data is wiped from it before they skip it or give it away. I
explain deleting from within windows doesn't really cut it and suggest
running dban if they want to be 100% certain. Naturally this wipes the
OS though, and if they want to give it away it is far more useful to the
recipient with an OS installed. Of course I could reinstall Windows for
them (assuming they have an install disk) which would get it running
nice and smooth again but then I'd have to charge them for the time it
took which could be substantial. If the machine is running OK I will
suggest using 'eraser' instead as it leaves the machine in a usable state.

The other use case is when people have had a work laptop at home for
ages and have maybe been doing 'things' with it that they wouldn't want
their colleagues/bosses to happen across evidence of. If they ever need
to return it they want to make sure there's no trace of their private
business on there.

Anyway, I have almost no customers using linux and it's not (always!) as
much of a chore to install after a wipe however, I was just curious if
there was a linux equivalent and whether it was more/less thorough than
'eraser'. It looks like 'shred' is it, and although it isn't as
featureful it should be plenty good enough for most potential use cases.

Roger.
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