Does rsync verify its writes?

Robin Lee Powell robinleepowell at
Fri Feb 17 16:51:50 UTC 2023

That's not the same as a read-back write verification.

I believe that in general, rsync assumes that the disk actually
wrote whatever it was told to write.

However, a second pass with --checksum will, in fact, read the
entirety of both files; if a --checksum run doesn't actually
transfer anything, you can safely conclude the files are
byte-for-byte[1] identical (or you have a serious low-level problem
where the disk is lying to you, which rsync is definitely not going
to be able to fix).

[1]: Technically they might not be byte-for-byte identical if you
somehow get identical hashing blocks, but Schneier once compared
that sort of thing to the survival time of a mouse on the surface of
the sun, so....  :D

On Fri, Feb 17, 2023 at 11:18:59AM +0100, anubis23 via rsync wrote:
> Hi,
> you can use the switch --fsync to verify the transfer. From the manpage:
> --fsync
>               Cause the receiving side to fsync each finished file.
> This may slow down the transfer, but can help to
>               provide peace of mind when updating critical files.
> -- 
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