[Reproducible-commits] [reproducible-builds-howto] 01/03: Mention timestamp in archives

[Jérémy Bobbio]

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lunar pushed a commit to branch master
in repository reproducible-builds-howto.

commit e14d50028ddb4f3a97b29f606b534db5668a0b9c
Author: Jérémy Bobbio <lunar at debian.org>
Date:   Sat Aug 1 20:09:52 2015 +0200

    Mention timestamp in archives
---
 reproducible-builds-howto.mdwn | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/reproducible-builds-howto.mdwn b/reproducible-builds-howto.mdwn
index 67a68cf..03ffc9e 100644
--- a/reproducible-builds-howto.mdwn
+++ b/reproducible-builds-howto.mdwn
@@ -116,6 +116,15 @@ Another option is to implement support for the `SOURCE_DATE_EPOCH` environment v
 
 Timestamps can creep in many unexpected places, but file modification times in archives might be the most common trap.
 
+Watch out for timestamps in archives
+------------------------------------
+
+Most archive formats will record the latest modification time of every files in their metadata. If files added to the archive are created during the build process, the archive will differ from one build to the next.
+
+Some tools will allow to specify a specific timestamp on the command line (e.g. Tar has `--mtime`) to solve this. In all cases, it is possible to set the modification time (`touch`) of the files before adding them to an archive. XXX: link to previous section
+
+Static libraries (`.a`) on Unix-like systems are archives. XXX: document binutils `--enable-deterministic-archives`.
+
 Avoid true randomness
 ---------------------
 

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