Scrub free disk blocks

Robert Nichols rnicholsNOSPAM at
Sat Aug 28 13:31:49 UTC 2010

On 08/27/2010 11:53 PM, JD wrote:
>    On 08/27/2010 09:25 PM, JD wrote:
>>   Is there a Linux util to scrub free disk blocks and keep everything
>> else intact ??
> Someone (not on this list) described a simple way to do this.
> Scrubbing files to be deleted is easy enough - there are utils for it
> already.
> But scrubbing existing free space is slower and requires patience.
> cd to the root of the partition.
> sudo dd if=/dev/zero of=ZERO bs=20M
> When the dd program fails to write any further, you
> have grabbed and zeroed all available free disk blocks
> in the partition.
> Now all you do is use the command scrub to scrub the file ZERO
> and when done  the file is deleted.

You need to do that as the UID permitted to use the reserved blocks
if you really want to clear _all_ the free space.  Note that if the
drive has reallocated any bad sectors there could still be some old
data present on the disk.

Bob Nichols     "NOSPAM" is really part of my email address.
                 Do NOT delete it.

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