Re: Default number of overwrites in shred

[Pádraig Brady]

Philip Rowlands wrote:
> On Fri, 4 May 2007, Paul Eggert wrote:
> 
>> Anyway, 'shred' currently does the first, but not the second, as it
>> doesn't verify what it's written.  That should get fixed, no?
> 
> Is there a way to ensure reading directly from disk? On Linux I see only
> a whole-system, root-level way to drop cached files [1].
> 
> 
> Cheers,
> Phil
> 
> [1] http://www.linuxinsight.com/proc_sys_vm_drop_caches.html

We discussed posix_fadvise(POSIX_FADV_DONTNEED) a while back actually:
http://lists.gnu.org/archive/html/bug-coreutils/2007-03/msg00039.html
Currently _on linux_ that will invalidate the cache for a file,
rather than a process. I.E. it currently does what you want.
I.E. if many processes have referenced pages of a file, then they are
still dropped when any process make the above call.
Note I don't think the spec should/does intend this.

A better option I think is to use O_DIRECT, but again
portability is going to be the issue here.

Pádraig.