Re: secure erasure of files?

[Andrew Morton <akpm@zip.com.au>]

Jan Hudec wrote:
> 
> > I don't know if any filesystem currently relocates blocks if you
> > overwrite a file, but it's certainly possible and allowed (everything
> > else except the filesystem itself simply must not care where the data
> > actually ends up on the disk).
> 
> AFAIK, ext2 tries to defragment files when possible.

We wish.

> Thus if the file was
> fragmented and the blocks after some fragment are free, it will use these
> instead of the original ones somewhere far apart.

Nope - if you're overwriting a part of the file which already has
allocated blocks, ext2/3 will use the same blocks.

Of course, the disk itself may decide to go and remap the block
if it decides that part of the media is getting tired.

-