Re: [Dar-support] dar creating corrupted archives

[Denis C. <dar...@fr...>]

Le 17/12/2025 à 13:43, Paul Neuwirth via Dar-support a écrit :
> On Tue, 16 Dec 2025 16:15:00 +0100
> Denis Corbin via Dar-support <dar...@li...> wrote:
[...]
>>
>> This is more the filesystem where dar backups are stored that are of
>> interest here, which one it is?
> 
> the destination is a NFSv4 mount, btrfs on the nfs server.

OK, no problem here neither writing backups to NFSv4, I use it often.

[...]

>>
>> Can you try reading/testing the corrupted backup in sequential read
>> mode (add --sequential-read option when testing the archive)?
>>
> 
> /backup # dar --sequential-read -t backup-roothomeFull
> Final memory cleanup...
> FATAL error, aborting operation: Error while reading in-place path
> using tape marks//.localbackup-snapshots/localbackup-20251215-100708 is
> an not a valid path: Empty string as subdirectory does not make a valid
> path

OK, this is a known bug in 2.7.18 (you were using 2.7.12 here), the 
archive can be read normally in sequential-read mode only, using dar 
version >= 2.7.18.

This bug was triggered by the double slash in the path.

With a fixed release, you can repair the archive/backup to also be able 
to read in direct access mode (if only using sequential read mode, no 
need to repair):

dar -y fixed_backup -A broken_backup [... other options if needed]

refer to documentation for the available options in repair mode.

> 
> interesting, that suggests something different?

I've tested in non sequential-read mode this same bug leads to dar 
reporting a corrupted archive the same way as you report.

This is the root cause of the problem you met.

> 
> 
>>>
>>> Do you have any idea? consulting search machines and chatGPT didn't
>>> result in anything useful.
>>
>> Well ChatGPT is good to make relations between existing information
>> and find the statistical most probable answer... but not to
>> investigate nor to solve problems that no one else ever met so far ;)
>>
>> My suggestions (ChatDenis's suggestions):
>>
>> 1/ Could you try reading in sequential read mode (add
>> --sequential-read option when testing the archive)?
>>
>> 2/ Could you use the official 2.7.19 dar_static version to build your
>> backup.
>> https://dar.edrusb.org/dar.linux.free.fr/Releases/Dar_static/
>>
>> We will see the next step with the result of these two suggestions.
>>
> 
> Thank you for the effort. based on your suggestions and the changes I
> did I'll try these things:
> -installed dar + backup to a local file system (btrfs)
> -installed dar + gzip instead of bzip2
> -dar_static with existing options and maybe the other, if those also
> fail.
> and I might take a look in the patches in those -bp... rpms if error
> doesn't occur with the dar_static.
> 
> When starting those tests I noticed some flaws in my backup scripts I
> need to fix along. I will report as soon I have above results. Might
> take a day.

for the dar side of the problem, no need to go further: this is a known 
bug fixed in release 2.7.18 (May 2025). You should upgrade your version 
to 2.7.19 or 2.8.2.

> 
> Best wishes
> Paul
> 

Cheers,
Denis