Re: [rdiff-backup-users] File change detection using hashes

[Wiebe Cazemier]

On 02/15/06 20:34, dean gaudet wrote:

>
>what you really want is something akin to rsync -c ... which forces 
>checksumming of every file, regardless of mtime/size.
>  
>
Well, that's basicly what my --checksum-diffs suggestion, which I
suggested in that feature request in october, would do. Calculate the
checksum of a file, compare it to what rdiff-backup has stored in it's
metafiles and decide to backup the file if the checksums are different.

>throwing more stat elements into the comparison is only approximately an 
>improvement (you could also throw in dev:inode -- which would handle your 
>mv situation most of the time, but breaks in some cases like snapshotting 
>which preserves inode without preserving dev).
>  
>
>>And, would it be possible to check for changes occured in files _during_
>>a backup with ctimes? That would be more reliable then mtimes.
>>    
>>
>
>ctime doesn't change when you modify the file, only mtime does.
>
The ctime (the change time of the inode) changes *always*. And, it
cannot be set by any application, so it would be an accurate detection.

But, I do agree that I would much rather have checksum comparisons than
another stat comparison, it's the most robust, and acts well when
backing up a system which has just been restored _from_ a backup (since
that would have a new ctime for every file).

And of course, checking for changes in special files like blockdevices
still has to happen the old fashion way, which shouldn't be a problem...

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