Re: cross-platform backup tool Same files from different source dir causes spurious diff files

Interesting,

If it helps I would say my use case is trying to preserve the "correct" 
view of the metadata, not the shifted view presented through a locally 
mounted logical volume. The backups I'm hoping to create whether from 
the running vm or a snapshot can always be used to restore parts back 
into the running vm. Right now my backups for this vm have been 
corrupted by the shifted UID/GIDs I can no longer use that archive to 
restore to the running vm.

Sure if I wanted to stop the vm then mount it's system image I could 
restore to that, but I'd rather not have to reboot my system just to get 
some files back.

I guess I'm also suggesting that the --user-mapping-file is 
bidirectional and undoes those changes during a restore.

     Best,
     Clif

On 2/9/22 10:30 PM, [email protected] wrote:
> Hi,
>
> On 09/02/2022 21:46, Mr. Clif wrote:
>> It would be great if rdiff-backup would allow offsets like this or 
>> even better the ability to specify a range like
>> 100000-165535:0-65535
>> Or you could just have the starting UID after the colon.
>>
>> In the man page under USERS AND GROUPS, it says:
>> "If you specify both --preserve-numerical-ids and one of the mapping 
>> options, the behavior is undefined."
>>
>> I think it would be better to allow both with the user-mapping-file 
>> overriding the preserve-numerical-ids behavior when necessary. As in 
>> my use case I never want user name mapping.
>
> The user mapping file is only used to save the files on disk, it isn't 
> used in the metadata so it wouldn't help in your case.
> Anyway, we already have an enhancement record in this regard: 
> https://github.com/rdiff-backup/rdiff-backup/issues/621
>
> I'm personally not sure that it's a good idea: a backup is there to 
> save things alike, not to modify them, so it's a dangerous road IMHO.
>
> KR, Eric
>