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Re: tar incremental backups and ctimeâ problem
- From: Vince Rice <vrice at solidrocksystems dot com>
- To: Cygwin Mailing List <cygwin at cygwin dot com>
- Date: Mon, 23 May 2016 10:24:07 -0500
- Subject: Re: tar incremental backups and ctimeâ problem
- Authentication-results: sourceware.org; auth=none
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> On Mon, May 23, 2016 at 5:29 PM, Eric Blake <email@example.com> wrote:
>> On 05/23/2016 03:18 AM, x y wrote:
>>> It is not clear to me your expectation:
>>> - are you asking how to use ctime to select the file with tar alone ?
>>> It is not possible for my understanding of the manual.
>>> - Are you asking the package maintainer to change the behaviour of
>>> cygwin tar ? Unlikely to happen, but I leave to him.
>>> Hi Marco,
>>> Sorry, I am new to the mailing list. If I am not wrong, tar is
>>> checking both of the ctime and mtime values to compare files during
>>> incremental backups. Since opening and closing a MS document without
>>> changing the content updates ctime, it would be preferable to add a
>>> new option to tar to use only mtime for file comparing during
>>> incremental backups.
>> 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
> 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
This is ultimately Ericâs decision, butâ
It doesnât _have_ to be solved. If someone wants to use Cygwin tar as a backup, then that someone lives with the fact that tar uses ctime. The differential might be a little too big, but no actual harm is done. So what.
I personally donât want to have to guess at tarâs behavior. I want to know itâs the same on Cygwin as elsewhere.
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