This change https://github.com/eggert/tz/commit/baea52df7ac9c4b53857556f... was a huge pain in my ass in 2013.
I was working in Libya on voter registration tools with the UN and the High National Election Commission. The government decided to not implement a planned TZ change, and didn't inform the public until the day of. Not the hardest thing we dealt with, that was a full country internet shutoff by a mob outside our data centre (https://www.bbc.com/news/world-africa-25481794). Sometimes the politics of a project are more complicated than the technology...
We did implement an all-SMS voter registration system, which was pretty cool. Hasn't been used much since, but it's all open source. https://github.com/hnec-vr
In How the tz database works (2020)eggert
tz
C2014–2026
eggert / tz
tz
Time zone database and code
38Distinct people
46Mentions
1Explicit recommenders
1.9KGitHub stars
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Time zone database and code
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I recommend anyone interested to look at some of the documentation done in the IANA timezone dataset (historical references of Finland shown here):…
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| Period | Start (UTC) | End (exclusive, UTC) | Mentions | Submissions | Comments |
|---|---|---|---|---|---|
| 2014 | 2014-01-01 00:00:00 UTC | 2015-01-01 00:00:00 UTC | 1 | 0 | 1 |
| 2015 | 2015-01-01 00:00:00 UTC | 2016-01-01 00:00:00 UTC | 1 | 0 | 1 |
| 2016 | 2016-01-01 00:00:00 UTC | 2017-01-01 00:00:00 UTC | 2 | 0 | 2 |
| 2017 | 2017-01-01 00:00:00 UTC | 2018-01-01 00:00:00 UTC | 0 | 0 | 0 |
| 2018 | 2018-01-01 00:00:00 UTC | 2019-01-01 00:00:00 UTC | 5 | 2 | 3 |
| 2019 | 2019-01-01 00:00:00 UTC | 2020-01-01 00:00:00 UTC | 2 | 0 | 2 |
| 2020 | 2020-01-01 00:00:00 UTC | 2021-01-01 00:00:00 UTC | 2 | 0 | 2 |
| 2021 | 2021-01-01 00:00:00 UTC | 2022-01-01 00:00:00 UTC | 5 | 0 | 5 |
| 2022 | 2022-01-01 00:00:00 UTC | 2023-01-01 00:00:00 UTC | 2 | 0 | 2 |
| 2023 | 2023-01-01 00:00:00 UTC | 2024-01-01 00:00:00 UTC | 5 | 0 | 5 |
| 2024 | 2024-01-01 00:00:00 UTC | 2025-01-01 00:00:00 UTC | 7 | 0 | 7 |
| 2025 | 2025-01-01 00:00:00 UTC | 2026-01-01 00:00:00 UTC | 5 | 0 | 5 |
| 2026 (partial) | 2026-01-01 00:00:00 UTC | 2027-01-01 00:00:00 UTC | 9 | 1 | 8 |
From the project README
An excerpt from the repository, fetched Nov 13, 2026.
Read the project’s introduction
README for the tz distribution
“Where do I set the hands of the clock?” – Les Tremayne as The King
“Oh that – you can set them any place you want.” – Frank Baxter as The Scientist
(from the Bell System film “About Time”)
The Time Zone Database (called tz, tzdb or zoneinfo) contains code and
data that represent the history of local time for many representative
locations around the globe. It is updated periodically to reflect
changes made by political bodies to time zone boundaries, UTC offsets,
and daylight-saving rules.
See <https://data.iana.org/time-zones/tz-link.html> or the
file tz-link.html for how to acquire the code and data.
Once acquired, read the leading comments in the file ‘Makefile’
and make any changes needed to make things right for your system,
especially when using a platform other than current GNU/Linux.
Then run the following commands, substituting your desired
installation directory for ‘$HOME/tzdir’:
make TOPDIR="$HOME/tzdir" install
"$HOME/tzdir/usr/bin/zdump" -v America/Los_Angeles
See the file tz-how-to.html for examples of how to read the data files.
This database of historical local time information has several goals:
* Provide a compendium of data about the history of civil time that
is useful even if not 100% accurate.
* Give an idea of the variety of local time rules that have existed
in the past and thus may be expected in the future.
* Test the generality of the local time rule description system.
The information in the time zone data files is by no means authoritative;
fixes and enhancements are welcome. Please see the file CONTRIBUTING
for details.
Thanks to these Time Zone Caballeros who’ve made major contributions to the
time conversion package: Keith Bostic; Bob Devine; Paul Eggert; Robert Elz;
Guy Harris; Mark Horton; John Mackin; and Bradley White. Thanks also to
Michael Bloom, Art Neilson, Stephen Prince, John Sovereign, and Frank Wales
for testing work, and to Gwillim Law for checking local mean time data.
Thanks in particular to Arthur David Olson, the project’s founder and first
maintainer, to whom the time zone community owes the greatest debt of all.
None of them are responsible for remaining errors.
-----
This file is in the public domain, so clarified as of 2009-05-17 by
Arthur David Olson. The other files in this distribution are either
public domain or BSD licensed; see the file LICENSE for details.
Read the full README on GitHubWhat Hacker News says
5 sourcesI've found the comments in the database files (e.g. North America https://github.com/eggert/tz/blob/main/northamerica ) to be an interesting documentation of the history of the definition of time for various areas. For example, Indiana https://github.com/eggert/tz/blob/main/northamerica#L846
In How the tz database works (2020)Oh by the way, check this out, this is one of the news in 2025b tzdata:
# From Roozbeh Pournader (2025-03-18):
# ... the exact time of Iran's transition from +0400 to +0330 ... was Friday
# 1357/8/19 AP=1978-11-10. Here's a newspaper clip from the Ettela'at
# newspaper, dated 1357/8/14 AP=1978-11-05, translated from Persian
# (at https://w.wiki/DUEY):
# Following the government's decision about returning the official time
# to the previous status, the spokesperson for the Ministry of Energy
# announced today: At the hour 24 of Friday 19th of Aban (=1978-11-10),
# the country's time will be pulled back half an hour.
From https://github.com/eggert/tz/blob/main/asia#L1503.
Pretty sure we can find a lot more oddities that are way worse.
In How to Think About Time in ProgrammingThe reason the zones use city names is because city identity is far more stable than national or regional borders. Still, the system can gracefully handle deprecation of a zone name. If Paris is renamed NewNewYork by edict of some new global despot, the IANA will just alias the two names together.
See https://github.com/eggert/tz/blob/main/backward for all the deprecated zones.
In JavaScript Temporal is comingIf I understand [1] correctly, two new zones (or one new one and the old one) would be created in that case. E.g. if Strasbourg would be occupied by Germany in 2027, a new Europe/Strasbourg could be created which has the same rules as Europe/Paris until 2026, and the rules of Europe/Berlin as of 2027.
[1] https://en.wikipedia.org/wiki/Tz_database
--
By the way, I looked up the time zone in Crimea.
> On 29 March 2014, after annexation by Russia, Crimea switched from Eastern European Time (UTC+02:00) to Moscow Time (UTC+04:00 then, subsequently changed to UTC+03:00). [2]
Crimea has its own zone in the IANA database, Europe/Simferopol, which was updated in 2014 (and already existed before, as it already used Moscow time from 1994 to 1997). [3]
[2] https://en.wikipedia.org/wiki/Time_in_Ukraine
[3] https://lists.iana.org/hyperkitty/list/tz@ian