Bug: rsync erroneously changes modification time

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Bug: rsync erroneously changes modification time

Samba - rsync mailing list
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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Re: Bug: rsync erroneously changes modification time

Samba - rsync mailing list
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.
>
>
>
>
> -------------------------------------------------
>
> ONLY AT VFEmail! - Use our Metadata Mitigator to keep your email out of
> the NSA's hands!
> $24.95 ONETIME Lifetime accounts with Privacy Features! 15GB disk! No
> bandwidth quotas!
> Commercial and Bulk Mail Options!
--
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        Kevin Korb Phone:    (407) 252-6853
        Systems Administrator Internet:
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Re: Bug: rsync erroneously changes modification time

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How exactly does rsync determine that the copy has the incorrect  
timestamp and not the source file?
Does it assume that the copy must be incorrect or are there other  
criteria that have to be considered?


Quoting Kevin Korb via rsync <[hidden email]>:

> 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.
>>
>>
>>
>>
>> -------------------------------------------------
>>
>> ONLY AT VFEmail! - Use our Metadata Mitigator to keep your email out of
>> the NSA's hands!
>> $24.95 ONETIME Lifetime accounts with Privacy Features! 15GB disk! No
>> bandwidth quotas!
>> Commercial and Bulk Mail Options!
>
> --
> ~*-,._.,-*~'`^`'~*-,._.,-*~'`^`'~*-,._.,-*~'`^`'~*-,._.,-*~'`^`'~*-,._.,
> Kevin Korb Phone:    (407) 252-6853
> Systems Administrator Internet:
> FutureQuest, Inc. [hidden email]  (work)
> Orlando, Florida [hidden email] (personal)
> Web page: http://www.sanitarium.net/
> PGP public key available on web site.
> ~*-,._.,-*~'`^`'~*-,._.,-*~'`^`'~*-,._.,-*~'`^`'~*-,._.,-*~'`^`'~*-,._.,




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Re: Bug: rsync erroneously changes modification time

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At 08:11 12.06.2017, max.power--- via rsync wrote:
>Content-Transfer-Encoding: 7bit
>Content-Disposition: inline
>
>How exactly does rsync determine that the copy has the incorrect  
>timestamp and not the source file?
>Does it assume that the copy must be incorrect or are there other  
>criteria that have to be considered?

rsync is only synching one way, it's always going from source to dest.
Therefore source is always 'correct' whereas dest will be adjusted to
match source. If you want a two way synching you'd need to call
rsync twice with different parameters (and switched source/dest)
or use a different tool.

bye  Fabi


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Re: Bug: rsync erroneously changes modification time

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In reply to this post by Samba - rsync mailing list
On Mon 12 Jun 2017, max.power--- via rsync wrote:

> How exactly does rsync determine that the copy has the incorrect timestamp
> and not the source file?

The source by definition is correct.


Paul

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Re: Bug: rsync erroneously changes modification time

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Ok, that clears things up.

Thanks.

Quoting Paul Slootman via rsync <[hidden email]>:

> On Mon 12 Jun 2017, max.power--- via rsync wrote:
>
>> How exactly does rsync determine that the copy has the incorrect timestamp
>> and not the source file?
>
> The source by definition is correct.
>
>
> Paul
>
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> Please use reply-all for most replies to avoid omitting the mailing list.
> To unsubscribe or change options:  
> https://lists.samba.org/mailman/listinfo/rsync
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