On Sun, Nov 22, 2020 at 04:43:21AM +0000, Gareth Evans wrote: > Hi all, > > I have asked this question on both the rsync mailing list and serverfault.com > but got no response from either.
Please, don't hijack threads. > I would be grateful, if this isn't too off-topic, if anyone could explain the > following: > > man rsync for -H includes: > > "If you specify a --link-dest directory that contains hard links, the linking > of the destination files against the --link-dest files can cause some paths > in the destination to become linked together due to the --link-dest > associations." > > How and/or why does this happen? What sort of scenario might lead to it? The way I understand it is this: Suppose whithin --link-dest, files A and B are hard-linked together. Now suppose you have two files in your source, say A' and B', with equal content to A and B (and thus equal themselves, but /not/ linked). You rsync with --link-dest and with -H. Now due to --link-dest, rsync sees "ah, A' == A, so I'll create A'' on dest hard linked to A'...". Same goes with B and its kin. Now you end up with two files A'' and B'' on dest which are hard linked to A' and B' on link-dest which are hard linked together. Due to how hard links work (they are all just directory entries pointing all to the same i-node), A'' and B'' are hard linked together. Somewhat contradicting your expectation set by -H (preserve hard links), since the sources A and B had equal content but weren't hard linked. This is all, of course, a hunch, and should be backed (or falsified) by code study and/or experimental evidence, which is left as an exercise for the reader ;-) Cheers - t
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