Re: what does rsync do when an input file changes?
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tirsdag 3. juni 2003, 23:16, skrev Conrad Newton:
> I have heard of people successfully using rsync to download
> a corrected version of a corrupted CD---only the corrections
> were downloaded, not the whole CD. This was over a modem.
> I hope your connection is not any slower than that!
> > I've also considered running rsync multiple times, so that on successive
> > passes it will pick up the changes. I just hope that the first pass
> > won't generate inconsistent files on the target side if the file changes
> > in the middle.
> This was the first idea that occured to me, too. I would guess
> that more sophisticated procedures are possible, but I do not
> know what they might be.
The math behind rsync can be (and has been) proved to be correct, which means
that if there aren't any implementation errors that idea will always work.
There is, of course, the remote chance of your checksums matching despite the
file being corrupted - but that's really remote. It might be impossible to do
deliberately without brute-forcing the hash function, and as for chance -
I believe that the quantum vacuum spontaneously collapsing to a lower energy
state, thereby killing all of us and essentially destroying the universe, is
more likely than two identical MD5 checksums appearing by chance.
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