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Date:	Mon, 23 May 2016 19:56:32 +0300
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Subject:	=?UTF-8?Q?Re=3A_tar_incremental_backups_and_ctime=E2=80=8F_problem?=
From:	x y <x1y2w3 AT gmail DOT com>
To:	cygwin AT cygwin DOT com
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>It is always possible to create file list with find and use that
>to tar whatever using --files-from=FILE option

>I don't see the need to change tar behaviour to meet your wish.

Hi Marco,

Consider that you are working in the IT department of a company and
you have thousands of documents in your file server. Concerning the
--file-from option, how can you guess the name of the files which are
just only going to be viewed by the workers? Those files would be not
modified but since the ctime stamp will be updated, they will be
included in the next incremental backup. Why to lose time with the
--files-from option and make things more difficult? Adding an option
to tar.exe to ignore the cname time stamp during differential \
incremental backups should be possible. This should be the natural
method. Tools like rsync does not suffer from such problems so my
request should make sense.

On Mon, May 23, 2016 at 6:35 PM, Marco Atzeri <marco DOT atzeri AT gmail DOT com> wrote:
> On 23/05/2016 16:57, x y wrote:
>>>
>>> mtime is fakeable, ctime is not.  Using only mtime makes it likely that
>>> your incremental backup will miss files.  I don't have any good reason
>>> to differ from upstream behavior here.
>>
>>
>> Hi Eric,
>>
>> The problem is not faking time stamps. Even commercial Windows backup
>> programs are checking the modification time to identify the modified
>> files.
>>
>> Consider that you have a lot of files opened and closed without any
>> modification in your company. Because of the priority of the ctime
>> time stamp, reintroducing all of those files to the incremental backup
>> does not make any sense. tar has also the capacity to create
>> differential backups with the condition of taking care of the snapshot
>> file. The ctime issue can result in unnecessarily big differential
>> backups filled with unmodified files.
>>
>> Cygwin tar can be a good  alternative for Windows users to do
>> differential \ incremental backups but the ctime problem must be
>> solved.
>>
>
> It is always possible to create file list with find and use that
> to tar whatever using --files-from=FILE option
>
> I don't see the need to change tar behaviour to meet your wish.
>
>
> Regards
> Marco
>
>
>
>
>
>
>
>
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