[Git][reproducible-builds/reproducible-website][master] Add a note re. TZ=UTC vs. TZ=UTC0

[Chris Lamb (@lamby)]

Chris Lamb pushed to branch master at Reproducible Builds / reproducible-website


Commits:
adf38b87 by Chris Lamb at 2026-09-29T10:45:22-07:00
Add a note re. TZ=UTC vs. TZ=UTC0

- - - - -


1 changed file:

- _docs/timezones.md


Changes:

=====================================
_docs/timezones.md
=====================================
@@ -43,6 +43,19 @@ Tue, 19 Jan 2038 03:14:07 +0000
 {% endhighlight %}
 </div>
 
+Note that `TZ=UTC` is *technically* invalid, although it will work on all
+observed `libc` implementations. [Chapter 8 of the POSIX standard](https://pubs.opengroup.org/onlinepubs/9799919799/basedefs/V1_chap08.html)
+states that the `TZ` format should be:
+
+```
+std offset [dst [offset][, rule]]
+```
+
+… where `std` and `offset` are required. In particular, the definition of
+`offset` states "The hour (*hh*) shall be required and may be a single digit. The
+*offset* following *std* shall be required." Therefore `TZ=UTC` is technically
+invalid as it misses the required offset; `TZ=UTC0` would be compliant.
+
 A related concern is for formats which don't contain timezone
 information. Zip archives are a good example: the same timezone must
 always be used to unpack them to prevent variations on the file



View it on GitLab: https://salsa.debian.org/reproducible-builds/reproducible-website/-/commit/adf38b870244e4cc9bed50c1b5c70a7a647ac66a

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View it on GitLab: https://salsa.debian.org/reproducible-builds/reproducible-website/-/commit/adf38b870244e4cc9bed50c1b5c70a7a647ac66a
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