Tarballs contain mtimes. They will not be reproducible if files have been generated or patched during build time.

[[https://reproducible.debian.net/issues/timestamps_in_tarball_issue.html|Known affected packages]]

= Detection =

[[attachment:allegro4.4_4.4.2-5.debbindiff.html|Example debbindiff output]]

= Work-around =

Known yet.

= Solutions =

== --mtime ==

If indivdiual mtimes don't matter, then use the `--mtime` option:

{{{
     --mtime=DATE-OR-FILE
           set mtime for added files from DATE-OR-FILE
}}}

== --clamp-mtime ==

tar/1.28-1 in Debian supports the `--clamp-mtime` option which will only adjust files with a modification time later than the time specified with `--mtime`.

{{{
SOURCE_DATE := $(shell dpkg-parsechangelog --show-field=Date)

        tar --clamp-mtime --mtime="$(SOURCE_DATE)" -cf archive.tar src
}}}

== Adjusting mtimes by modifying timestamps in disk ==

Use `find`, `xargs`, and `touch` to adjust file mtimes before `tar` is run. Example:

{{{
SOURCE_DATE := $(shell dpkg-parsechangelog --show-field=Date)
[…]
       find '$(DIR)' -newermt '$(SOURCE_DATE)' -print0 | \
               xargs -0r touch --no-dereference --date='$(SOURCE_DATE)'
       […] tar […]
}}}