## page was renamed from ReproducibleBuilds/TimestampInPDFGeneratedByLaTeX
PDF files generated with pdftex and pdflatex will contain !CreationDate and !ModDate set to the current date and time. The [[http://sources.debian.net/src/texlive-bin/latest/texk/web2c/pdftexdir/utils.c/#L693|PDF ID]] is also generated using the current time, path and file name.

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

= Detection =

[[attachment:splash_2.5.0-1.debbindiff.html|Example debbindiff output]]

Lintian will probably never check this, because extracting the timestamp from a PDF requires external dependencies, and knowing the build date requires the Debian changelog, which may be missing if for example /usr/share/doc/package links to another package. 

= Work-around =

The PDF produced by the following Makefile snippet does not seem to depend on current date,
time zone
or absolute path.
The ID generation emulates PDFTeX's behaviour, but
uses the date of the last Debian changelog entry,
and ignores the unpredictible current absolute path.
The file name, however, is mentioned by {{{du}}}.
{{{#!highlight makefile
DEB_DATE := $(shell dpkg-parsechangelog -S date)
PDF_DATE := $(shell date -ud '$(DEB_DATE)' +D:%Y%m%d%H%M%SZ)
tmp.pdf: tmp.tex
	pdflatex '\pdfinfo{/CreationDate($(PDF_DATE))/ModDate($(PDF_DATE))}\input{$<}'
	MD5=`(echo $(DEB_DATE) && du -b $@) | md5sum | cut -c -32` && \
	sed -i "s|^/ID \\[\\(<[0-9A-F]\\{32\\}>\\) \\1]$$|/ID [<$$MD5> <$$MD5>]|" $@
}}}
The PDF ID field is optional, and may safely be removed completely by replacing the two last lines with
{{{#!highlight makefile
	grep -av '^/ID \[\(<[0-9A-F]\{32\}>\) \1]$$' $@ > $@.without_pdf_id
	mv -f $@.without_pdf_id $@
}}}

= Solution =

A patch has been sent to pdftex upstream which expands on a previous patch, see[[http://tug.org/pipermail/pdftex/2015-May/008940.html|previous thread]]. The [[http://tug.org/pipermail/pdftex/2015-July/008952.html|new patch]] honours the implementation of the environment variable SOURCE_DATE_EPOCH. This was proposed as a way to produce deterministic timestamps, see [[https://wiki.debian.org/ReproducibleBuilds/TimestampsProposal|timestamps proposal]].


Another option for Debian would be to remove the field completely with dh_installdocs or similar, or at least set its content consistently (package build date, installation directory, and so on).
Current situation may cause PDF files indirectly depending on the architecture to be installed into /usr/share, breaking Multiarch:same packages.

DebianPts:apparmor uses the file modification time instead of the current time. See [[http://sources.debian.net/src/apparmor/latest/parser/Makefile/?hl=120:124#L120|Makefile]] and [[http://sources.debian.net/src/apparmor/latest/parser/techdoc.tex/?hl=11:14#L1|LaTeX source]]. But this does not solve the PDF ID.