SOURCE_DATE_EPOCH and timezone with FAT images

Holger Levsen holger at layer-acht.org
Tue Mar 29 23:43:59 UTC 2022


Hi Thomas,

sorry for only getting back to you on this a month later...
(and only very specifically on one aspect of your email.)

On Wed, Feb 23, 2022 at 08:54:05PM +0100, Thomas Schmitt wrote:
> I quoted https://reproducible-builds.org/docs/source-date-epoch/:
> > >   "At present, we do not have a proposal that includes anything
> > >    resembling a "time zone"."
> 
> > Oh yeah, that does sound a little unhelpful out of context today.
> 
> How about:
> 
>   We demand to apply timezone UTC whenever a timezone is involved in
>   formatting timestamps at build time. Beyond this demand, we currently
>   do not have a proposal that includes anything resembling a "time zone".

I think this would be an excellent addition! Could you please file a 
merge request via https://salsa.debian.org/reproducible-builds/reproducible-website/
though please note however that the quoted paragraph is below a heading 
called "History and alternative proposals", so that I've actually just done 
a commit removing the 'At present' quoted above.

I think part of the confusion here is applying a timezone to SOURCE_DATE_EPOCH
at all, something we never considered, as "obviously" SOURCE_DATE_EPOCH are
the seconds since the epoch, which is an UTC timestamp.

I'm not sure how to clarify https://reproducible-builds.org/docs/source-date-epoch/
further but I'm also sure I'm too close and too entangled to see. As such, 
and as always, feedback and patches very welcome.

I guess a sentence like 'SOURCE_DATE_EPOCH specifies the last modification of
the source (measured) in seconds since the unix epoch which is January 1st 1970,
00:00:00 UTC.' on top of https://reproducible-builds.org/docs/source-date-epoch/
would be helpful.

I'm also sure this is far from perfect, so please improve:

commit 3764949f50fe3d8f557de2b4d26e740f55760c31 (HEAD -> master, origin/master)
Author: Holger Levsen <holger at layer-acht.org>
Date:   Wed Mar 30 01:42:39 2022 +0200

    explain SOURCE_DATE_EPOCH on /docs/source_date_epoch
    
    Signed-off-by: Holger Levsen <holger at layer-acht.org>

diff --git a/_docs/source-date-epoch.md b/_docs/source-date-epoch.md
index 21718ae..822d7b3 100644
--- a/_docs/source-date-epoch.md
+++ b/_docs/source-date-epoch.md
@@ -4,8 +4,11 @@ layout: docs
 permalink: /docs/source-date-epoch/
 ---
 
+
 `SOURCE_DATE_EPOCH` is a [standardised environment variable](https://reproducible-builds.org/specs/source-date-epoch/) that distributions can set centrally and have build tools consume this in order to produce reproducible output.
 
+In practice `SOURCE_DATE_EPOCH` specifies the last modification of something, usually the source code, (measured) in seconds since the unix epoch, which is January 1st 1970, 00:00:00 UTC.


& thanks, too!

-- 
cheers,
	Holger

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