[CentOS] evaluating backup systems: rsync

Robert Nichols rnicholsNOSPAM at comcast.net
Sun Jan 20 03:44:56 UTC 2013

On 01/19/2013 01:21 PM, John Hinton wrote:
> On 1/19/2013 1:28 PM, Nicolas Thierry-Mieg wrote:
>> See man rsync:
>> Rsync  finds  files that need to be transferred using a “quick check”
>> algorithm (by default) that looks for files that have changed in size or
>> in last-modified time.
>> and yes I've tested this before posting  ;-)
>> to avoid this you need to use --size-only .
> Yet size only is not reliable. If for instance you have a simple text
> file with the word hellO and someone catches the typo and changes it to
> hello, the filesize doesn't change as near as I can see. Both show as 6
> using ls -al. Unless rsync uses a more granular check of filesize that I
> am not aware of? If this is the case, then someone could potentially
> edit a large document fixing numerous simple typos and wind up with the
> same filesize.

And then there is prelink, which changes the contents of files without
changing either the size** or the modification time. It's the topic of some
very messy code and nasty comments in my backup scripts.

** The very first time a file is prelinked, the size will change. Subsequent
    prelink runs may change the content, but will not affect the size.

Bob Nichols     "NOSPAM" is really part of my email address.
                 Do NOT delete it.

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