Aw: Re: rsync doesn't checksum for local transfers?

[devzero at web.de]

> You are missing the point of the checksum.  It is a verification that
> the file was assembled on the target system correctly.  The only
> post-transfer checksum that would make any sense locally would be to
> make sure that the disk stored the file correctly which would require
> a flushing of the cache and a re-reading of the file.  Rsync has no
> capability to do this whether remote or not.

yes, but indeed this could be explained more clearly in the manpage

> > """Note that rsync always verifies that each transferred file was 
> > correctly reconstructed on the receiving side by checking a
> > whole-file checksum that is generated as the file is
> > transferred"""

let me try to add some lines :

After being written to disk, for both local and remote transfers,  the 
destination file as a whole is not being re-read for checksumming. 
Checksumming is only being done for the reconstruction process: 
The checksum is calculated across the bits being received and the 
bits being read from the target file, so essentially the updated 
target file is being checksummed while it`s being written to.

is that correct ?

> 
> On 12/03/2014 09:17 PM, Shriramana Sharma wrote:
> > Hello. Please see http://unix.stackexchange.com/a/66702. I would
> > like to have confirmation whether or not rsync verifies the
> > transferred files' integrity at the target location by checksumming
> > as advertised in the manpage:
> > 
> > """Note that rsync always verifies that each transferred file was 
> > correctly reconstructed on the receiving side by checking a
> > whole-file checksum that is generated as the file is
> > transferred"""
> > 
> > The word "always" here seems to indicate that the integrity check
> > will happen whether for local or network transfers, but the above
> > Stack Exchange post claims otherwise. Please clarify.
> > 
> > Also, once it is assured that the check will happen *really*
> > "always", it would be useful to advertise the fact about the
> > integrity check in the website and description part of the manpage
> > itself IMO.
> > 
> > FWIW I'm using rsync 3.1.1 (latest) on openSUSE Tumbleweed.
> > 
> > Thanks.
> > 
> 
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