Re: dar creating corrupted archives

On Tue, 16 Dec 2025 16:15:00 +0100
Denis Corbin via Dar-support <[email protected]> wrote:

> > 
> > exact command run:
> > dar   -c /backup/backup-roothomeFull -@
> > /backup/backup-roothomeFull.cat -R
> > //.localbackup-snapshots/localbackup-20251215-100708 -zbzip2:9 -m 0
> > -v -D -N -w -Q --hash sha1 --user-comment '%h %d %c'
> > --retry-on-change 3 -g"root" -P "*/.Trash*" -P ".Trash*" -P
> > "*/.mozilla/*/[Cc]ache" -P "*/.opera/[Cc]ache*" -P
> > "*/.pan/*/[Cc]ache" -P "*/.thumbnails" -P "*/.beagle" -P
> > "root/.opera/" -P "root/.cache/" -P "root/clamav-quarantine/"  -an
> > -Z "*.dar" -Z "*.crypt" -Z "*.arj" -Z "*.bz2" -Z "*.bz" -Z "*.Z" -Z
> > "*.tgz" -Z "*.taz" -Z "*.cpio" -Z "*.deb" -Z "*.gtar" -Z "*.gz" -Z
> > "*.lzh" -Z "*.lhz" -Z "*.rar" -Z "*.rpm" -Z "*.shar" -Z "*.sv4cpi"
> > -Z "*.sv4crc" -Z "*.ustar" -Z "*.zoo" -Z "*.zip" -Z "*.jar" -Z
> > "*.jpg" -Z "*.gif" -Z "*.mpg" -Z "*.mpeg" -Z "*.avi" -Z "*.ram" -Z
> > "*.rm" -Z "*.7z" -Z "*.xz" -Z "*.lz" -Z "*.lzma" -Z "*.lz4" -Z
> > "*.zst" -Z "*.txz" -Z "*.tbz" -Z "*.tbz2" -Z "*.apk" -Z "*.war" -Z
> > "*.msi" -Z "*.cab" -Z "*.pkg" -Z "*.snap" -Z "*.jpeg" -Z "*.jpe" -Z
> > "*.png" -Z "*.webp" -Z "*.tif" -Z "*.tiff" -Z "*.mp3" -Z "*.ogg" -Z
> > "*.oga" -Z "*.opus" -Z "*.flac" -Z "*.m4a" -Z "*.aac" -Z "*.wma" -Z
> > "*.mp4" -Z "*.m4v" -Z "*.mkv" -Z "*.mov" -Z "*.wmv" -Z "*.flv" -Z
> > "*.webm" -Z "*.docx" -Z "*.xlsx" -Z "*.pptx" -Z "*.odt" -Z "*.ods"
> > -Z "*.odp" -ac
> > 
> > (/.localbackup-snapshots/localbackup-20251215-100708/ in this case
> > is a btrfs snapshot created by my backup script of the root
> > filesystem)  
> 
> btrfs and snapshot is not a problem, they appear to dar as normal 
> filesystem to backup.
> 
> 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.

> > 
> > everything looks fine besides these "Failed resaving uncompressed
> > the inode data", but the created .dar files are unusable!?  
> 
> Then "Failed resaving uncompressed" are effectively weird:
> - when a compressed file takes more space than its uncompressed size, 
> dar truncates the dar backup to the location where the backup for
> that file was starting and then restart the backup without
> compression that particular file.
> 
> Either truncate() system call failed, or something in the lower
> libdar layers (caching layer, here there is no slicing so this is
> even simpler)
> 
> 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

interesting, that suggests something different?


> > 
> > 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.

Best wishes
Paul