[linux-elitists] rsync hacks (fwd from kragen@pobox.com)

Martin Pool mbp@sourcefrog.net
Mon Jul 19 16:23:03 PDT 2004


On 19 Jul 2004, Sam Phillips <sam@dasbistro.com> wrote:
> 
> On Fri, Jul 16, 2004, at 12:58 CDT, Tilghman Lesher wrote:
> > On Friday 16 July 2004 12:39, Sam Phillips wrote:
> > > On Thu, Jul 15, 2004, at 09:54 +0200, Eugen Leitl wrote:
> > > > Figured this could be useful for somebody here.
> > > >
> > > > On Wed, 14 Jul 2004 at 11:37:06, Kragen Sitaker wrote:
> > > > > rsync is a remarkably versatile program.  Here are some of the recent
> > > > > uses I have for it.
> > >
> > > Now does anyone know a way for rsync to not alter the atime on files
> > > that I'm backing up?
> > 
> > Yeah, mount your filesystem -o noatime.  Seriously, though, you can't
> > normally.  Atime (or last access time) is a function of the filesystem, and
> > as you need to access the file in order to back it up, atime _must_ be
> > changed, or else atime isn't reliable (and if it's not reliable, why have it
> > at all?).
> 
> See, what we need is a way for a single process (or process group) to
> behave like it has noatime set when it runs.  That one process would never
> adjust the atime and all of the other processes on the system would
> remain normal.

Even better might be an O_NOATIME flag, so that all other files can work
normally.  I think Hurd already has this, so when we all switch to GNU Hurd
in 2001 it will be OK.  In the meantime maybe somebody should do it on Linux.

Unfortunately since atime is handy for security forensics it probably needs
to be root only or tied into the capabilities mess. 

-- 
Martin
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