SOURCE_DATE_EPOCH and timezone with FAT images

Holger Levsen holger at
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
> > >   "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
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
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
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>
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>

diff --git a/_docs/ b/_docs/
index 21718ae..822d7b3 100644
--- a/_docs/
+++ b/_docs/
@@ -4,8 +4,11 @@ layout: docs
 permalink: /docs/source-date-epoch/
 `SOURCE_DATE_EPOCH` is a [standardised environment variable]( 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!


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