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author	Philip Paeps <philip@FreeBSD.org>	2022-08-16 08:09:47 +0000
committer	Philip Paeps <philip@FreeBSD.org>	2022-08-16 08:09:47 +0000
commit	a24d752d3e77a28c877a5319face8d00aa1b558c (patch)
tree	5ae147d3bedd850833ec5c783ea54fa4b00e6aba /tz-link.html
parent	9b5369d383baf54651be0922591eeb6263ce029d (diff)

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+<!DOCTYPE html>

+<html lang="en">

+<head>

+<title>Time zone and daylight saving time data</title>

+<meta charset="UTF-8">

+<style>

+pre {margin-left: 2em; white-space: pre-wrap;}

+</style>

+</head>

+<body>

+<h1>Time zone and daylight saving time data</h1>

+<p>

+<a href="https://en.wikipedia.org/wiki/Time_zone">Time zone</a> and

+<a href="https://en.wikipedia.org/wiki/Daylight_saving_time">daylight-saving</a>

+rules are controlled by individual

+governments. They are sometimes changed with little notice, and their

+histories and planned futures are often recorded only fitfully. Here

+is a summary of attempts to organize and record relevant data in this

+area.

+</p>

+ <h3>Outline</h3>

+ <nav>

+ <ul>

+ <li>The <code><abbr>tz</abbr></code> database product and process

+ <ul>

+ <li><a href="#tzdb">The <code><abbr>tz</abbr></code> database</a></li>

+ <li><a href="#download">Downloading the <code><abbr>tz</abbr></code> database</a></li>

+ <li><a href="#changes">Changes to the <code><abbr>tz</abbr></code> database</a></li>

+ <li><a href="#commentary">Commentary on the <code><abbr>tz</abbr></code> database</a></li>

+ </ul>

+ </li>

+ <li>Uses of the <code><abbr>tz</abbr></code> database

+ <ul>

+ <li><a href="#web">Web sites using recent versions of the <code><abbr>tz</abbr></code> database</a></li>

+ <li><a href="#protocols">Network protocols for <code><abbr>tz</abbr></code> data</a></li>

+ <li><a href="#compilers">Other <code><abbr>tz</abbr></code> compilers</a></li>

+ <li><a href="#TZif">Other <abbr>TZif</abbr> readers</a></li>

+ <li><a href="#software">Other <code><abbr>tz</abbr></code>-based time zone software</a></li>

+ </ul>

+ </li>

+ <li>Related data

+ <ul>

+ <li><a href="#other-dbs">Other time zone databases</a></li>

+ <li><a href="#maps">Maps</a></li>

+ <li><a href="#boundaries">Time zone boundaries</a></li>

+ </ul>

+ </li>

+ <li>Timekeeping concepts

+ <ul>

+ <li><a href="#civil">Civil time concepts and history</a></li>

+ <li><a href="#national">National histories of legal time</a></li>

+ <li><a href="#costs">Costs and benefits of time shifts</a></li>

+ <li><a href="#precision">Precision timekeeping</a></li>

+ <li><a href="#notation">Time notation</a></li>

+ </ul>

+ </li>

+ <li><a href="#see-also">See also</a></li>

+ </ul>

+ </nav>

+<section>

+<h2 id="tzdb">The <code><abbr title="time zone">tz</abbr></code> database</h2>

+<p>

+The <a href="https://en.wikipedia.org/wiki/Public_domain">public-domain</a>

+time zone database 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 and daylight saving rules.

+This database (known as <code><abbr>tz</abbr></code>,

+<code><abbr>tzdb</abbr></code>, or <code>zoneinfo</code>)

+is used by several implementations,

+including

+<a href="https://www.gnu.org/software/libc/">the

+<abbr title="GNU's Not Unix">GNU</abbr>

+C Library</a> (used in

+<a href="https://en.wikipedia.org/wiki/Linux"><abbr>GNU</abbr>/Linux</a>),

+<a href="https://www.android.com">Android</a>,

+<a href="https://www.freebsd.org">Free<abbr

+title="Berkeley Software Distribution">BSD</abbr></a>,

+<a href="https://netbsd.org">Net<abbr>BSD</abbr></a>,

+<a href="https://www.openbsd.org">Open<abbr>BSD</abbr></a>,

+<a href="https://www.chromium.org/chromium-os/">Chromium OS</a>,

+<a href="https://cygwin.com">Cygwin</a>,

+<a href="https://mariadb.org">MariaDB</a>,

+<a href="https://en.wikipedia.org/wiki/MINIX">MINIX</a>,

+<a href="https://www.mysql.com">MySQL</a>,

+<a href="https://en.wikipedia.org/wiki/WebOS"><abbr

+title="Web Operating System">webOS</abbr></a>,

+<a href="https://en.wikipedia.org/wiki/IBM_AIX"><abbr

+title="Advanced Interactive eXecutive">AIX</abbr></a>,

+<a href="https://www.apple.com/ios"><abbr

+title="iPhone OS">iOS</abbr></a>,

+<a href="https://www.apple.com/macos">macOS</a>,

+<a href="https://www.microsoft.com/en-us/windows">Microsoft Windows</a>,

+<a href="https://www.vmssoftware.com">Open<abbr

+title="Virtual Memory System">VMS</abbr></a>,

+<a href="https://www.oracle.com/database/">Oracle Database</a>, and

+<a href="https://www.oracle.com/solaris">Oracle Solaris</a>.</p>

+<p>

+Each main entry in the database represents a <dfn>timezone</dfn>

+for a set of civil-time clocks that have all agreed since 1970.

+Timezones are typically identified by continent or ocean and then by the

+name of the largest city within the region containing the clocks.

+For example, <code>America/New_York</code>

+represents most of the <abbr title="United States">US</abbr> eastern time zone;

+<code>America/Phoenix</code> represents most of Arizona, which

+uses mountain time without daylight saving time (<abbr>DST</abbr>);

+<code>America/Detroit</code> represents most of Michigan, which uses

+eastern time but with different <abbr>DST</abbr> rules in 1975;

+and other entries represent smaller regions like Starke County,

+Indiana, which switched from central to eastern time in 1991

+and switched back in 2006.

+To use the database on an extended <a

+href="https://en.wikipedia.org/wiki/POSIX"><abbr

+title="Portable Operating System Interface">POSIX</abbr></a>

+implementation set the <code><abbr>TZ</abbr></code>

+environment variable to the location's full name,

+e.g., <code><abbr>TZ</abbr>="America/New_York"</code>.</p>

+<p>

+Associated with each timezone is a history of offsets from

+<a href="https://en.wikipedia.org/wiki/Universal_Time">Universal

+Time</a> (<abbr>UT</abbr>), which is <a

+href="https://en.wikipedia.org/wiki/Greenwich_Mean_Time">Greenwich Mean

+Time</a> (<abbr>GMT</abbr>) with days beginning at midnight;

+for timestamps after 1960 this is more precisely <a

+href="https://en.wikipedia.org/wiki/Coordinated_Universal_Time">Coordinated

+Universal Time</a> (<abbr>UTC</abbr>).

+The database also records when daylight saving time was in use,

+along with some time zone abbreviations such as <abbr>EST</abbr>

+for Eastern Standard Time in the <abbr>US</abbr>.</p>

+</section>

+<section>

+<h2 id="download">Downloading the <code><abbr>tz</abbr></code> database</h2>

+<p>

+The following <a

+href="https://en.wikipedia.org/wiki/Unix_shell">shell</a> commands download

+the latest release's two

+<a href="https://en.wikipedia.org/wiki/Tar_(computing)">tarballs</a>

+to a <abbr>GNU</abbr>/Linux or similar host.</p>

+<pre><code>mkdir tzdb

+cd tzdb

+<a href="https://www.gnu.org/software/wget/">wget</a> https://www.iana.org/time-zones/repository/tzcode-latest.tar.gz

+wget https://www.iana.org/time-zones/repository/tzdata-latest.tar.gz

+<a href="https://www.gnu.org/software/gzip/">gzip</a> -dc tzcode-latest.tar.gz | <a href="https://www.gnu.org/software/tar/">tar</a> -xf -

+gzip -dc tzdata-latest.tar.gz | tar -xf -

+</code></pre>

+<p>Alternatively, the following shell commands download the same

+release in a single-tarball format containing extra data

+useful for regression testing:</p>

+<pre><code>wget <a href="https://www.iana.org/time-zones/repository/tzdb-latest.tar.lz">https://www.iana.org/time-zones/repository/tzdb-latest.tar.lz</a>

+<a href="https://www.nongnu.org/lzip/">lzip</a> -dc tzdb-latest.tar.lz | tar -xf -

+</code></pre>

+<p>These commands use convenience links to the latest release

+of the <code><abbr>tz</abbr></code> database hosted by the

+<a href="https://www.iana.org/time-zones">Time Zone Database website</a>

+of the <a href="https://www.iana.org">Internet Assigned Numbers

+Authority (IANA)</a>.

+Older releases are in files named

+<code>tzcode<var>V</var>.tar.gz</code>,

+<code>tzdata<var>V</var>.tar.gz</code>, and

+<code>tzdb-<var>V</var>.tar.lz</code>,

+where <code><var>V</var></code> is the version.

+Since 1996, each version has been a four-digit year followed by

+lower-case letter (<samp>a</samp> through <samp>z</samp>,

+then <samp>za</samp> through <samp>zz</samp>, then <samp>zza</samp>

+through <samp>zzz</samp>, and so on).

+Since version 2022a, each release has been distributed in

+<a href="https://pubs.opengroup.org/onlinepubs/9699919799/utilities/pax.html#tag_20_92_13_06">POSIX

+ustar interchange format</a>, compressed as described above;

+older releases use a nearly-compatible format.

+Since version 2016h, each release has contained a text file named

+"<samp>version</samp>" whose first (and currently only) line is the version.

+Older releases are <a href="https://ftp.iana.org/tz/releases/">archived</a>,

+and are also available in an

+<a href="ftp://ftp.iana.org/tz/releases/"><abbr

+title="File Transfer Protocol">FTP</abbr> directory</a> via a

+less-secure protocol.</p>

+<p>Alternatively, a development repository of code and data can be

+retrieved from <a href="https://github.com">GitHub</a> via the shell

+command:</p>

+<pre><code><a href="https://git-scm.com">git</a> clone <a href="https://github.com/eggert/tz">https://github.com/eggert/tz</a>

+</code></pre>

+<p>

+Since version 2012e, each release has been tagged in development repositories.

+Untagged commits are less well tested and probably contain

+more errors.</p>

+<p>

+After obtaining the code and data files, see the

+<code>README</code> file for what to do next.

+The code lets you compile the <code><abbr>tz</abbr></code> source files into

+machine-readable binary files, one for each location. The binary files

+are in a special timezone information format (<dfn><abbr>TZif</abbr></dfn>)

+specified by <a href="https://datatracker.ietf.org/doc/html/8536">Internet

+<abbr>RFC</abbr> 8536</a>.

+The code also lets

+you read a <abbr>TZif</abbr> file and interpret timestamps for that

+location.</p>

+</section>

+<section>

+<h2 id="changes">Changes to the <code><abbr>tz</abbr></code> database</h2>

+<p>

+The <code><abbr>tz</abbr></code> code and data

+are by no means authoritative. If you find errors, please

+send changes to <a href="mailto:tz@iana.org"><code>tz@iana.org</code></a>,

+the time zone mailing list. You can also <a

+href="https://mm.icann.org/mailman/listinfo/tz">subscribe</a> to it

+and browse the <a

+href="https://mm.icann.org/pipermail/tz/">archive of old

+messages</a>.

+<a href="https://tzdata-meta.timtimeonline.com/">Metadata for mailing list

+discussions</a> and corresponding data changes can be

+generated <a href="https://github.com/timparenti/tzdata-meta">automatically</a>.

+</p>

+<p>

+If your government plans to change its time zone boundaries or

+daylight saving rules, inform <code>tz@iana.org</code> well in

+advance, as this will coordinate updates to many cell phones,

+computers, and other devices around the world.

+The change should be officially announced at least a year before it affects

+how clocks operate; otherwise, there is a good chance that some

+clocks will operate incorrectly after the change, due

+to delays in propagating updates to software and data. The shorter

+the notice, the more likely clock problems will arise; see "<a

+href="https://codeofmatt.com/2016/04/23/on-the-timing-of-time-zone-changes/">On

+the Timing of Time Zone Changes</a>" for examples.

+The <code><abbr>tz</abbr></code> data can represent planned changes

+far into the future, and a long-planned change can easily be reverted

+or otherwise altered with a year's notice before the change would have

+affected clocks.

+</p>

+<p>

+Changes to the <code><abbr>tz</abbr></code> code and data are often

+propagated to clients via operating system updates, so

+client <code><abbr>tz</abbr></code> data can often be corrected by

+applying these updates. With GNU/Linux and similar systems, if your

+maintenance provider has not yet adopted the

+latest <code><abbr>tz</abbr></code> data, you can often short-circuit

+the process by tailoring the generic instructions in

+the <code><abbr>tz</abbr> README</code> file and installing the latest

+data yourself. System-specific instructions for installing the

+latest <code><abbr>tz</abbr></code> data have also been published

+for <a href="https://developer.ibm.com/articles/au-aix-olson-time-zone/"><abbr>AIX</abbr></a>,

+<a

+href="https://source.android.com/devices/tech/config/timezone-rules">Android</a>,

+<a

+href="https://unicode-org.github.io/icu/userguide/datetime/timezone/"><abbr

+title="International Components for Unicode">ICU</abbr></a>,

+<a href="https://www.ibm.com/support/pages/java-sdk-time-zone-update-utility"><abbr>IBM</abbr>

+JDK</a>,

+<a href="https://www.joda.org/joda-time/tz_update.html">Joda-Time</a>, <a

+href="https://dev.mysql.com/doc/refman/en/time-zone-support.html">MySQL</a>,

+<a href="https://nodatime.org/userguide/tzdb">Noda Time</a>, and <a

+href="https://www.oracle.com/java/technologies/javase/tzupdater-readme.html">OpenJDK/Oracle JDK</a>.

+</p>

+<p>Since version 2013a,

+sources for the <code><abbr>tz</abbr></code> database have been

+<a href="https://en.wikipedia.org/wiki/UTF-8"><abbr

+title="Unicode Transformation Format 8-bit">UTF-8</abbr></a>

+<a href="https://en.wikipedia.org/wiki/Text_file">text files</a>

+with lines terminated by <a href="https://en.wikipedia.org/wiki/Newline"><abbr

+title="linefeed">LF</abbr></a>,

+which can be modified by common text editors such

+as <a href="https://www.gnu.org/software/emacs/">GNU Emacs</a>,

+<a href="https://wiki.gnome.org/Apps/Gedit">gedit</a>, and

+<a href="https://www.vim.org">vim</a>.

+Specialized source-file editing can be done via the

+<a href="https://packagecontrol.io/packages/zoneinfo">Sublime

+zoneinfo</a> package for <a

+href="https://www.sublimetext.com">Sublime Text</a> and the <a

+href="https://marketplace.visualstudio.com/items?itemName=gilmoreorless.vscode-zoneinfo">VSCode

+zoneinfo</a> extension for <a href="https://code.visualstudio.com">Visual

+Studio Code</a>.

+</p>

+<p>

+For further information about updates, please see

+<a href="https://datatracker.ietf.org/doc/html/rfc6557">Procedures for

+Maintaining the Time Zone Database</a> (Internet <abbr

+title="Request For Comments">RFC</abbr> 6557). More detail can be

+found in <a href="theory.html">Theory and pragmatics of the

+<code><abbr>tz</abbr></code> code and data</a>.

+<a href="https://a0.github.io/a0-tzmigration/">A0 TimeZone Migration</a>

+displays changes between recent <code><abbr>tzdb</abbr></code> versions.

+</p>

+</section>

+<section>

+<h2 id="commentary">Commentary on the <code><abbr>tz</abbr></code> database</h2>

+<ul>

+<li>The article

+<a href="https://en.wikipedia.org/wiki/Tz_database">tz database</a> is

+an encyclopedic summary.</li>

+<li><a href="tz-how-to.html">How to Read the

+tz Database Source Files</a> explains the <code><abbr>tz</abbr></code>

+database format.</li>

+<li><a

+href="https://blog.jonudell.net/2009/10/23/a-literary-appreciation-of-the-olsonzoneinfotz-database/">A

+literary appreciation of the Olson/Zoneinfo/tz database</a> comments on the

+database's style.</li>

+<li><a href="https://doi.org/10.1145/3340301.3341125">What time is it:

+managing time in the internet</a> analyzes the database longitudinally.</li>

+</ul>

+</section>

+<section>

+<h2 id="web">Web sites using recent versions of the

+<code><abbr>tz</abbr></code> database</h2>

+<p>

+These are listed roughly in ascending order of complexity and fanciness.

+</p>

+<ul>

+<li><a href="https://time.is">Time.is</a> shows locations'

+time and zones.</li>

+<li><a href="https://www.timejones.com">TimeJones.com</a>,

+<a href="https://timezoneconverterapp.com">Time Zone Converter</a> and

+<a href="https://www.worldclock.com">The World Clock</a>

+are time zone converters.</li>

+<li><a href="https://timezonedb.com/download">TimeZoneDB Database</a>

+publishes <code><abbr>tzdb</abbr></code>-derived data in

+<a href="https://en.wikipedia.org/wiki/Comma-separated_values"><abbr

+title="comma-separated values">CSV</abbr></a> and

+in <a href="https://en.wikipedia.org/wiki/SQL"><abbr

+title="Structured Query Language">SQL</abbr></a> form.</li>

+<li><a

+href="https://twiki.org/cgi-bin/xtra/tzdatepick.html">Date and Time Gateway</a>

+lets you see the <code><abbr>TZ</abbr></code> values directly.</li>

+<li><a

+href="https://www.convertit.com/Go/ConvertIt/World_Time/Current_Time.ASP">Current

+Time in 1000 Places</a> uses descriptions of the values.</li>

+<li><a href="https://home.kpn.nl/vanadovv/time/TZworld.html">Complete

+timezone information for all countries</a>

+displays tables of <abbr>DST</abbr> rules.

+<li><a href="https://www.timeanddate.com/worldclock/">The World Clock –

+Worldwide</a> lets you sort zone names and convert times.</li>

+<li><a href="https://24timezones.com">24TimeZones</a> has a world

+time map and a time converter.</li>

+<li><a href="https://www.zeitverschiebung.net/en/">Time Difference</a>

+calculates the current time difference between locations.</li>

+<li><a href="https://www.wx-now.com">Weather Now</a> and

+<a href="https://www.thetimenow.com">The Time Now</a> list the weather too.</li>

+</ul>

+</section>

+<section>

+<h2 id="protocols">Network protocols for <code><abbr>tz</abbr></code> data</h2>

+<ul>

+<li>The <a href="https://www.ietf.org">Internet Engineering Task Force</a>'s

+<a href="https://datatracker.ietf.org/wg/tzdist/charter/">Time Zone Data

+Distribution Service (tzdist) working group</a> defined <a

+href="https://datatracker.ietf.org/doc/html/rfc7808">TZDIST</a>

+(Internet <abbr>RFC</abbr> 7808), a time zone data distribution service,

+along with <a href="https://datatracker.ietf.org/doc/html/rfc7809">CalDAV</a>

+(Internet <abbr>RFC</abbr> 7809), a calendar access protocol for

+transferring time zone data by reference.

+<a href="https://devguide.calconnect.org/Time-Zones/TZDS/">TZDIST

+implementations</a> are available.

+The <a href="https://www.ietf.org/mailman/listinfo/tzdist-bis">tzdist-bis

+mailing list</a> discusses possible extensions.</li>

+<li>The <a href="https://datatracker.ietf.org/doc/html/rfc5545">

+Internet Calendaring and Scheduling Core Object Specification

+(iCalendar)</a> (Internet <abbr>RFC</abbr> 5445)

+covers time zone

+data; see its VTIMEZONE calendar component.

+The iCalendar format requires specialized parsers and generators; a

+variant <a href="https://datatracker.ietf.org/doc/html/rfc6321">xCal</a>

+(Internet <abbr>RFC</abbr> 6321) uses

+<a href="https://www.w3.org/XML/"><abbr

+title="Extensible Markup Language">XML</abbr></a> format, and a variant

+<a href="https://datatracker.ietf.org/doc/html/rfc7265">jCal</a>

+(Internet <abbr>RFC</abbr> 7265)

+uses <a href="https://www.json.org"><abbr

+title="JavaScript Object Notation">JSON</abbr></a> format.</li>

+</ul>

+</section>

+<section>

+<h2 id="compilers">Other <code><abbr>tz</abbr></code> compilers</h2>

+<p>Although some of these do not fully support

+<code><abbr>tz</abbr></code> data, in recent <code><abbr>tzdb</abbr></code>

+distributions you can generally work around compatibility problems by

+running the command <code>make rearguard_tarballs</code> and compiling

+from the resulting tarballs instead.</p>

+<ul>

+<li><a href="https://sourceforge.net/projects/vzic/">Vzic</a> is a <a

+href="https://en.wikipedia.org/wiki/C_%28programming_language%29">C</a>

+program that compiles

+<code><abbr>tz</abbr></code> source into iCalendar-compatible VTIMEZONE files.

+Vzic is freely

+available under the <a

+href="https://www.gnu.org/copyleft/gpl.html"><abbr>GNU</abbr>

+General Public License (<abbr

+title="General Public License">GPL</abbr>)</a>.</li>

+<li><a href="https://sourceforge.net/projects/tzical/">tziCal – tz

+database conversion utility</a> is like Vzic, except for the <a

+href="https://dotnet.microsoft.com">.NET framework</a>

+and with a <abbr>BSD</abbr>-style license.</li>

+<li><a

+href="https://metacpan.org/release/DateTime-TimeZone">DateTime::TimeZone</a>

+contains a script <code>parse_olson</code> that compiles

+<code><abbr>tz</abbr></code> source into <a href="https://www.perl.org">Perl</a>

+modules. It is part of the Perl <a

+href="https://github.com/houseabsolute/DateTime.pm/wiki">DateTime Project</a>,

+which is freely

+available under both the <abbr>GPL</abbr> and the Perl Artistic

+License. DateTime::TimeZone also contains a script

+<code>tests_from_zdump</code> that generates test cases for each clock

+transition in the <code><abbr>tz</abbr></code> database.</li>

+<li>The <a href="https://howardhinnant.github.io/date/tz.html">Time Zone

+Database Parser</a> is a

+<a href="https://en.wikipedia.org/wiki/C%2B%2B">C++</a> parser and

+runtime library with <a

+href="https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0355r7.html">API</a>

+adopted by

+<a href="https://en.wikipedia.org/wiki/C++20">C++20</a>,

+the current iteration of the C++ standard.

+It is freely available under the

+<abbr title="Massachusetts Institute of Technology">MIT</abbr> license.</li>

+<li><a id="ICU" href="https://icu.unicode.org">International Components for

+Unicode (<abbr>ICU</abbr>)</a> contains C/C++ and <a

+href="https://en.wikipedia.org/wiki/Java_%28programming_language%29">Java</a>

+libraries for internationalization that

+has a compiler from <code><abbr>tz</abbr></code> source

+and from <abbr title="Common Locale Data Repository">CLDR</abbr> data

+(mentioned <a href="#CLDR">below</a>)

+into an <abbr>ICU</abbr>-specific format.

+<abbr>ICU</abbr> is freely available under a

+<abbr>BSD</abbr>-style license.</li>

+<li>The <a href="https://github.com/lau/tzdata">Tzdata</a> package for

+the <a href="https://elixir-lang.org">Elixir</a> language downloads

+and compiles <code><abbr>tz</abbr></code> source and exposes <abbr

+title="Application Program Interface">API</abbr>s for use. It is

+freely available under the <abbr>MIT</abbr> license.</li>

+<li>Java-based compilers and libraries include:

+<ul>

+<li>The <a

+href="https://www.oracle.com/java/technologies/javase/tzupdater-readme.html">TZUpdater

+tool</a> compiles <code><abbr>tz</abbr></code> source into the format used by

+<a href="https://openjdk.java.net/">OpenJDK</a> and

+<a href="https://jdk.java.net/">Oracle JDK</a>.

+Although its source code is proprietary, its executable is available under the

+<a href="https://www.oracle.com/a/tech/docs/tzupdater-lic.html">Java SE

+Timezone Updater License Agreement</a>.</li>

+<li>The <a

+href="https://www.oracle.com/technetwork/articles/java/jf14-date-time-2125367.html">Java

+SE 8 Date and Time</a> <abbr>API</abbr> can be supplemented by <a

+href="https://www.threeten.org/threeten-extra/">ThreeTen-Extra</a>,

+which is freely available under a <abbr>BSD</abbr>-style license.</li>

+<li><a href="https://www.joda.org/joda-time/">Joda-Time – Java date

+and time <abbr>API</abbr></a> contains a class

+<code>org.joda.time.tz.ZoneInfoCompiler</code> that compiles

+<code><abbr>tz</abbr></code> source into a binary format. It inspired

+Java 8 <code>java.time</code>, which its users should migrate to once

+they can assume Java 8 or later. It is available under the <a

+href="https://www.apache.org/licenses/LICENSE-2.0">Apache License</a>.</li>

+<li><a href="https://bell-sw.com/pages/iana-updater/">IANA Updater</a> and <a

+href="https://www.azul.com/products/open-source-tools/ziupdater-time-zone-tool/">ZIUpdater</a>

+are alternatives to TZUpdater. IANA Updater's license is unclear;

+ZIUpdater is licensed under the <abbr>GPL</abbr>.</li>

+<li><a href="https://github.com/MenoData/Time4A">Time4A: Advanced date and

+time library for Android</a> and

+<a href="https://github.com/MenoData/Time4J/">Time4J: Advanced date,

+time and interval library for Java</a> compile

+<code><abbr>tz</abbr></code> source into a binary format.

+Time4A is available under the Apache License and Time4J is

+available under the <a

+href="https://www.gnu.org/copyleft/lesser.html"><abbr>GNU</abbr> Lesser

+General Public License (<abbr title="Lesser General Public

+License">LGPL</abbr>)</a>.</li>

+<li><abbr>ICU</abbr> (mentioned <a href="#ICU">above</a>) contains compilers and

+Java-based libraries.</li>

+</ul>

+<li><a href="https://nodatime.org">Noda Time – Date and

+time <abbr>API</abbr> for .NET</a>

+is like Joda-Time and Time4J, but for the .NET framework instead of Java.

+It is freely available under the Apache License.</li>

+<li>Many modern

+<a href="https://en.wikipedia.org/wiki/JavaScript">JavaScript</a>

+runtimes support <code><abbr>tz</abbr></code> natively via the

+<samp>timeZone</samp> option of <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/DateTimeFormat"><samp>Intl.DateTimeFormat</samp></a>.

+This can be used as-is or with most of the following libraries,

+many of which also support runtimes lacking the <samp>timeZone</samp> option.

+<ul>

+<li>The <a

+href="https://github.com/formatjs/date-time-format-timezone"><samp>Intl.DateTimeFormat</samp>

+timezone polyfill</a>

+is freely available under a <abbr>BSD</abbr>-style license.</li>

+<li>The <a href="https://date-fns.org/">date-fns</a>

+library manipulates timezone-aware timestamps in browsers and

+in <a href="https://nodejs.org/en/">Node.js</a>.

+It is freely available under the <abbr>MIT</abbr> license.</li>

+<li><a href="https://github.com/iamkun/dayjs">Day.js</a> is a

+minimalist replacement for the date and time API of

+the <a href="https://momentjs.com/docs/">now-legacy Moment.js</a> date

+manipulation library.

+It is freely available under the <abbr>MIT</abbr> license.</li>

+<li><a href="https://moment.github.io/luxon/">Luxon</a> improves

+timezone support for the <samp>Intl</samp> API.

+It is freely available under the <abbr>MIT</abbr> license.</li>

+<li><a href="https://momentjs.com/timezone/">Moment Timezone</a> is a

+Moment.js plugin.

+It is freely available under the <abbr>MIT</abbr> license.</li>

+<li><a href="https://github.com/bigeasy/timezone">Timezone</a> is a

+JavaScript library that supports date arithmetic that is time zone

+aware. It is freely available under the <abbr>MIT</abbr> license.</li>

+<li><a href="https://www.npmjs.com/package/@tubular/time">@tubular/time</a>

+supports live <code><abbr>tzdb</abbr></code> updates,

+astronomical and atomic time, a command-line interface,

+and full <a

+href="https://en.wikipedia.org/wiki/TypeScript">TypeScript</a>.

+Its companion <a

+href="https://www.npmjs.com/package/@tubular/time-tzdb">@tubular/time-tzdb</a>

+can generate <abbr>TZif</abbr> and other files, and a companion website

+<a href="https://tzexplorer.org">Timezone Database Explorer</a> lets you

+convert timestamps, view transition histories, and download code and data.

+It is freely available under the <abbr>MIT</abbr> license.</li>

+</ul>

+The proposed <a

+href="https://github.com/tc39/proposal-temporal"><samp>Temporal</samp>

+objects</a> let programs access an abstract view of

+<code><abbr>tzdb</abbr></code> data, and are designed to replace <a

+href="https://codeofmatt.com/javascript-date-type-is-horribly-broken/">JavaScript's

+problematic <samp>Date</samp> objects</a> when working with dates and times.

+<li><a href="https://github.com/JuliaTime/">JuliaTime</a> contains a

+compiler from <code><abbr>tz</abbr></code> source into

+<a href="https://julialang.org/">Julia</a>. It is freely available

+under the <abbr>MIT</abbr> license.</li>

+<li><a href="https://github.com/pavkam/tzdb"><abbr>TZDB</abbr> –

+<abbr>IANA</abbr> Time Zone Database for Delphi/<abbr

+title="Free Pascal Compiler">FPC</abbr></a>

+compiles from <code><abbr>tz</abbr></code> source into

+<a href="https://en.wikipedia.org/wiki/Object_Pascal">Object Pascal</a>

+as compiled by <a href="https://en.wikipedia.org/wiki/Delphi_(IDE)">Delphi</a>

+and <a

+href="https://en.wikipedia.org/wiki/Free_Pascal"><abbr>FPC</abbr></a>.

+It is freely available under a <abbr>BSD</abbr>-style license.</li>

+<li><a href="http://pytz.sourceforge.net">pytz – World Timezone

+Definitions for Python</a> compiles <code><abbr>tz</abbr></code> source into

+<a href="https://www.python.org">Python</a>.

+It is freely available under a <abbr>BSD</abbr>-style license.

+In code that can assume Python 3.6 or later it is largely superseded; see <a

+href="https://blog.ganssle.io/articles/2018/03/pytz-fastest-footgun.html">pytz:

+The Fastest Footgun in the West</a>.</li>

+<li><a href="https://tzinfo.github.io">TZInfo –

+Ruby Timezone Library</a>

+compiles <code><abbr>tz</abbr></code> source into

+<a href="https://www.ruby-lang.org/en/">Ruby</a>.

+It is freely available under the <abbr>MIT</abbr> license.</li>

+<li>The <a href="https://www.squeaksource.com/Chronos/">Chronos Date/Time

+Library</a> is

+a <a href="https://en.wikipedia.org/wiki/Smalltalk">Smalltalk</a> class

+library that compiles <code><abbr>tz</abbr></code> source into a time

+zone repository whose format

+is either proprietary or an <abbr>XML</abbr>-encoded

+representation.</li>

+<li><a id="Tcl" href="https://tcl.tk">Tcl</a>

+contains a developer-oriented parser that compiles <code><abbr>tz</abbr></code>

+source into text files, along with a runtime that can read those

+files. Tcl is freely available under a <abbr>BSD</abbr>-style

+license.</li>

+</ul>

+</section>

+<section>

+<h2 id="TZif">Other <abbr>TZif</abbr> readers</h2>

+<ul>

+<li>The <a

+href="https://www.gnu.org/software/libc/"><abbr>GNU</abbr> C

+Library</a>

+has an independent, thread-safe implementation of

+a <abbr>TZif</abbr> file reader.

+This library is freely available under the LGPL

+and is widely used in <abbr>GNU</abbr>/Linux systems.</li>

+<li><a href="https://www.gnome.org">GNOME</a>'s

+<a href="https://developer.gnome.org/glib/">GLib</a> has

+a <abbr>TZif</abbr> file reader written in C that

+creates a <code>GTimeZone</code> object representing sets

+of <abbr>UT</abbr> offsets.

+It is freely available under the <abbr>LGPL</abbr>.</li>

+<li>The

+<a href="https://github.com/bloomberg/bde/wiki">BDE Standard Library</a>'s

+<code>baltzo::TimeZoneUtil</code> component contains a C++

+implementation of a <abbr>TZif</abbr> file reader. It is freely available under

+the Apache License.</li>

+<li><a href="https://github.com/google/cctz">CCTZ</a> is a simple C++

+library that translates between <abbr>UT</abbr> and civil time and

+can read <abbr>TZif</abbr> files. It is freely available under the Apache

+License.</li>

+<li><a href="https://github.com/derickr/timelib">Timelib</a> is a C

+library that reads <abbr>TZif</abbr> files and converts

+timestamps from one time zone or format to another.

+It is used by <a href="https://secure.php.net"><abbr

+title="PHP: Hypertext Preprocessor">PHP</abbr></a>,

+<a href="https://hhvm.com"><abbr title="HipHop Virtual Machine">HHVM</abbr></a>,

+and <a href="https://www.mongodb.com">MongoDB</a>.

+It is freely available under the <abbr>MIT</abbr> license.</li>

+<li>Tcl, mentioned <a href="#Tcl">above</a>, also contains a

+<abbr>TZif</abbr> file reader.</li>

+<li><a href="https://metacpan.org/pod/DateTime::TimeZone::Tzfile">

+DateTime::TimeZone::Tzfile</a>

+is a <abbr>TZif</abbr> file reader written in Perl.

+It is freely available under the same terms as Perl

+(dual <abbr>GPL</abbr> and Artistic license).</li>

+<li>Python has a <a id="python-zoneinfo"

+href="https://docs.python.org/3/library/zoneinfo.html"><code>zoneinfo.ZoneInfo</code>

+class</a> that reads <abbr>TZif</abbr> data and creates objects

+that represent <code><abbr>tzdb</abbr></code> timezones.

+Python is freely available under the

+<a href="https://docs.python.org/3/license.html">Python Software Foundation

+License</a>.

+A companion <a id="pypi-tzdata" href="https://pypi.org/">PyPI</a> module

+<a href="https://pypi.org/project/tzdata/"><code>tzdata</code></a>

+supplies TZif data if the underlying system data cannot be found;

+it is freely available under the Apache License.</li>

+<li>The

+public-domain <a href="https://github.com/dbaron/tz.js">tz.js</a>

+library contains a Python tool that

+converts <abbr>TZif</abbr> data into

+<abbr>JSON</abbr>-format data suitable for use

+in its JavaScript library for time zone conversion. Dates before 1970

+are not supported.</li>

+<li>The <a

+href="https://hackage.haskell.org/package/timezone-olson">timezone-olson</a>

+package contains <a href="https://www.haskell.org">Haskell</a> code that

+parses and uses <abbr>TZif</abbr> data. It is freely

+available under a <abbr>BSD</abbr>-style license.</li>

+</ul>

+</section>

+<section>

+<h2 id="software">Other <code><abbr>tz</abbr></code>-based time zone software</h2>

+<ul>

+<li><a href="https://foxclocks.org">FoxClocks</a>

+is an extension for <a href="https://www.google.com/chrome/">Google

+Chrome</a> and for <a

+href="https://wiki.mozilla.org/Modules/Toolkit">Mozilla

+Toolkit</a> applications like <a

+href="https://www.mozilla.org/en-US/firefox/new/">Firefox</a> and <a

+href="https://www.mozilla.org/en-US/thunderbird/">Thunderbird</a>.

+It displays multiple clocks in the application window, and has a mapping

+interface to <a href="https://www.google.com/earth/">Google Earth</a>.

+It is freely available under the <abbr>GPL</abbr>.</li>

+<li><a href="https://golang.org">Go programming language</a>

+implementations contain a copy of a 32-bit subset of a recent

+<code><abbr>tz</abbr></code> database in a

+Go-specific format.</li>

+<li>Microsoft Windows 8.1

+and later has <code><abbr>tz</abbr></code> data and <abbr>CLDR</abbr>

+data (mentioned <a href="#CLDR">below</a>) used by the

+<a href="https://en.wikipedia.org/wiki/Windows_Runtime">Windows Runtime</a> /

+<a href="https://en.wikipedia.org/wiki/Universal_Windows_Platform">Universal Windows Platform</a> classes

+<a href="https://docs.microsoft.com/uwp/api/Windows.Globalization.DateTimeFormatting.DateTimeFormatter"><code>DateTimeFormatter</code></a> and

+<a href="https://docs.microsoft.com/uwp/api/windows.globalization.calendar"><code>Calendar</code></a>.

+<a id="System.TimeZoneInfo"

+href="https://blogs.msdn.microsoft.com/bclteam