Re: Incremental and permission changes

On 2026-02-05 09:33, Chris Wilkinson wrote:
> I was rather hoping that someone would suggest how to overcome this as 
> I
> keep running into the same issue.
> 
> -Chris
> 
> On Thu, 5 Feb 2026, 08:18 Andrea Venturoli, <[email protected]> wrote:
> 
>> On 2/2/26 10:13, Andrea Venturoli wrote:
>> > Hello.
>> >
>> > In an installation I manage, there's a NAS with lot of data that is
>> > backed up with the usual Full/Diff/Inc schedule.
>> > On this NAS it's quite frequent to have sweeping permission changes;
>> > alas these almost translate an Incremental backup into a Full one.
>> >
>> > I don't care about permissions: I can set them up automatically after a
>> > restore, so I'd like to avoid this.
>> >
>> > What's the proper way to tell Bacula NOT to backup a file if only its
>> > permission changed?
>> > Or, again, don't backup permissions at all, if the above is not feasible?
>> >
>> > I also thought about using "accurate: mco1", which should backup the
>> > permissions, but not the files themself. This could do...
>> > Before putting it into production, though, are there any caveat?
>> >
>> > Any other idea?
>> 
>> No one?
>> 
>>   bye & Thanks
>>         av.
>> 

Hello

If I understood the problem correctly, the solution is rather simple.
You can modify your file set and specify the option "mtimeonly = yes"
like this:

FileSet {
   Name = "your_fileset"
   Include {
     Options {
       mtimeonly = yes
       # ... other options like compression, fstype, etc.
     }
     File = /some_path
     # ...
   }
}

Here is the excerpt from Bacula documentation:

https://www.docs.baculasystems.com/BETechnicalReference/Director/DirectorResourceTypes/FilesetResource/index.html#technicalreferencedirfilesetresource

-----BEGIN-----
Mtime Only

     Description: If enabled, tells the Client that the selection of 
files
during Incremental and Differential backups should based only on the
st_mtime value in the stat() packet.

     Value(s): <No|Yes>

         Data Type:

     Comment: The default is no which means that the selection of files 
to
be backed up will be based on both the st_mtime and the st_ctime values.
In general, it is not recommended to use this option.

     Important

     When the Job resource is configured using accurate mode, it will 
take
precedence over the mtimeonly option used in the Fileset resource. It 
means
that the mtimeonly option will not be considered, but the accurate 
options
defined in the Fileset resource.
-----END-----


So, if you use Accurate = yes, you will need to configure Accurate 
flags:
     m compare the modification time (st_mtime)
     c compare the change time (st_ctime)
     s compare the size

By default, Bacula would use "accurate = mcs"


Note that file's ctime gets updated when at least one of the following 
changes
occur: permissions, ownership, group ownership, name, size, mtime, ACLs,
extended file system attributes related to a file.
I am not sure if I left something out.

So, in this particular case, ignoring ctime should be safe.
If the content of files change, the files would be selected for backup.

I like flexible software like Bacula. :-)


Regards

-- 
Josip Deanovic