Bug: rsync erroneously changes modification time

Kevin Korb kmk at sanitarium.net
Mon Jun 12 00:54:00 UTC 2017

Whenever you use --times (included in --archive) rsync will fix
incorrect time stamps.  The only thing --size-only is doing is keeping
the incorrect data instead of replacing it.

The purpose of these options is to "fix" a copy done in a way that did
not preserve timestamps but the data is known to have not changed.
These options allow rsync to correct the incorrect timestamps without
even looking inside of the files.  If you are not 100% sure your file
data matches you should not be using --size-only.

On 06/11/2017 09:28 AM, max.power--- via rsync wrote:
> When a file of same length already exists at the destination then the
> command 'rsync --archive --size-only' (--archive is same as -rlptgoD)
> may change the modification time of the destination file even if no
> modification was made.
> Type the following commands in a terminal in order to reproduce the
> problem:
> $ mkdir source
> $ mkdir target
> $ echo "file one" > source/file
> $ echo "file two" > target/file
> $ srcstamp=201111110000.11
> $ tgtstamp=200001010000.00
> $ touch -t $srcstamp source/file
> $ touch -t $tgtstamp target/file
> $ stat -c "%y %s" source/file
> $ stat -c "%y %s" target/file
> Notice, that although the file in source/ and target/ folder contain
> different content they do not  differ in size. Thus, there following
> command should not make any changes:
> $ rsync -rlptgoD --size-only source/ target
> There was indeed no backup performed, which can be verified by viewing
> the contents of the files:
> $ cat source/file
> $ cat target/file
> However, the modification time of the target file was updated to the
> same modification time as file in source/:
> $ stat -c "%y %s" source/file
> $ stat -c "%y %s" target/file
> Since the file was not modified the modification time should not be
> changed. Omitting the '-t' option in above rsync does not solve the
> problem because when a backup is actually performed then the
> modification time will simply be set to the current system time instead
> of the modification time of the source file.
> The same behaviour can be observed when using the flags -rlptgoD (or
> --archive) with the --checksum flag. Although it is highly unlikely that
> the files will differ if the checksums are the same, the modficaition
> should still not be changed for consistency reasons.
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	Kevin Korb			Phone:    (407) 252-6853
	Systems Administrator		Internet:
	FutureQuest, Inc.		Kevin at FutureQuest.net  (work)
	Orlando, Florida		kmk at sanitarium.net (personal)
	Web page:			http://www.sanitarium.net/
	PGP public key available on web site.

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