libc/time/tz-link.html

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1.1Schristos<title>Sources for time zone and daylight saving time data</title>
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1.1Schristos<h1>Sources for time zone and daylight saving time data</h1>
1.1Schristos<p>
1.1Schristos<a href="https://en.wikipedia.org/wiki/Time_zone">Time zone</a> and
1.1Schristos<a href="https://en.wikipedia.org/wiki/Daylight_saving_time">daylight-saving</a>
1.1Schristosrules are controlled by individual
1.1Schristosgovernments. They are sometimes changed with little notice, and their
1.1Schristoshistories and planned futures are often recorded only fitfully. Here
1.1Schristosis a summary of attempts to organize and record relevant data in this
1.1Schristosarea.
1.1Schristos</p>
1.1Schristos<h2 id="tzdb">The <code><abbr title="time zone">tz</abbr></code> database</h2>
1.1Schristos<p>
1.1SchristosThe <a href="https://en.wikipedia.org/wiki/Public_domain">public-domain</a>
1.1Schristostime zone database contains code and data
1.1Schristosthat represent the history of local time
1.1Schristosfor many representative locations around the globe.
1.1SchristosIt is updated periodically to reflect changes made by political bodies
1.1Schristosto time zone boundaries and daylight saving rules.
1.1SchristosThis database (known as <code><abbr>tz</abbr></code>,
1.1Schristos<code><abbr>tzdb</abbr></code>, or <code>zoneinfo</code>)
1.1Schristosis used by several implementations,
1.1Schristosincluding
1.1Schristos<a href="https://www.gnu.org/software/libc/">the
1.1Schristos<abbr title="GNU's Not Unix">GNU</abbr>
1.1SchristosC Library</a> (used in
1.1Schristos<a href="https://en.wikipedia.org/wiki/Linux"><abbr>GNU</abbr>/Linux</a>),
1.1Schristos<a href="https://www.android.com">Android</a>,
1.1Schristos<a href="https://www.freebsd.org">Free<abbr
1.1Schristostitle="Berkeley Software Distribution">BSD</abbr></a>,
1.1Schristos<a href="https://netbsd.org">Net<abbr>BSD</abbr></a>,
1.1Schristos<a href="https://www.openbsd.org">Open<abbr>BSD</abbr></a>,
1.1Schristos<a href="https://www.chromium.org/chromium-os">Chromium OS</a>,
1.1Schristos<a href="https://cygwin.com">Cygwin</a>,
1.1Schristos<a href="http://www.delorie.com/djgpp/"><abbr
1.1Schristostitle="DJ's GNU Programming Platform">DJGPP</abbr></a>,
1.1Schristos<a href="https://en.wikipedia.org/wiki/MINIX">MINIX</a>,
1.1Schristos<a href="https://www.mysql.com">MySQL</a>,
1.1Schristos<a href="https://en.wikipedia.org/wiki/WebOS"><abbr
1.1Schristostitle="Web Operating System">webOS</abbr></a>,
1.1Schristos<a href="https://ibm.com/aix"><abbr
1.1Schristostitle="Advanced Interactive eXecutive">AIX</abbr></a>,
1.1Schristos<a href="https://en.wikipedia.org/wiki/BlackBerry_10">BlackBerry 10</a>,
1.1Schristos<a href="https://www.apple.com/ios/"><abbr
1.1Schristostitle="iPhone OS">iOS</abbr></a>,
1.1Schristos<a href="https://www.apple.com/macos/">macOS</a>,
1.1Schristos<a href="https://www.microsoft.com/en-us/windows">Microsoft Windows</a>,
1.1Schristos<a href="https://www.hpe.com/info/openvms">Open<abbr
1.1Schristostitle="Virtual Memory System">VMS</abbr></a>,
1.1Schristos<a href="https://www.oracle.com/database/index.html">Oracle Database</a>, and
1.1Schristos<a href="https://www.oracle.com/solaris">Oracle Solaris</a>.</p>
1.1Schristos<p>
1.2SchristosEach main entry in the database represents a <dfn>timezone</dfn>
1.2Schristosfor a set of civil-time clocks that have all agreed since 1970.
1.2SchristosTimezones are typically identified by continent or ocean and then by the
1.2Schristosname of the largest city within the region containing the clocks.
1.1SchristosFor example, <code>America/New_York</code>
1.1Schristosrepresents most of the <abbr title="United States">US</abbr> eastern time zone;
1.1Schristos<code>America/Phoenix</code> represents most of Arizona, which
1.2Schristosuses mountain time without daylight saving time (<abbr>DST</abbr>);
1.1Schristos<code>America/Detroit</code> represents most of Michigan, which uses
1.1Schristoseastern time but with different <abbr>DST</abbr> rules in 1975;
1.1Schristosand other entries represent smaller regions like Starke County,
1.1SchristosIndiana, which switched from central to eastern time in 1991
1.1Schristosand switched back in 2006.
1.1SchristosTo use the database on an extended <a
1.1Schristoshref="https://en.wikipedia.org/wiki/POSIX"><abbr
1.1Schristostitle="Portable Operating System Interface">POSIX</abbr></a>
1.1Schristosimplementation set the <code><abbr>TZ</abbr></code>
1.1Schristosenvironment variable to the location's full name,
1.1Schristose.g., <code><abbr>TZ</abbr>="America/New_York"</code>.</p>
1.1Schristos<p>
1.2SchristosAssociated with each timezone is a history of offsets from
1.1Schristos<a href="https://en.wikipedia.org/wiki/Universal_Time">Universal
1.1SchristosTime</a> (<abbr>UT</abbr>), which is <a
1.1Schristoshref="https://en.wikipedia.org/wiki/Greenwich_Mean_Time">Greenwich Mean
1.1SchristosTime</a> (<abbr>GMT</abbr>) with days beginning at midnight;
1.2Schristosfor timestamps after 1960 this is more precisely <a
1.1Schristoshref="https://en.wikipedia.org/wiki/Coordinated_Universal_Time">Coordinated
1.1SchristosUniversal Time</a> (<abbr>UTC</abbr>).
1.1SchristosThe database also records when daylight saving time was in use,
1.1Schristosalong with some time zone abbreviations such as <abbr>EST</abbr>
1.1Schristosfor Eastern Standard Time in the <abbr>US</abbr>.</p>
1.1Schristos<h2 id="download">Downloading the <code><abbr>tz</abbr></code> database</h2>
1.1Schristos<p>
1.1SchristosThe following <a
1.1Schristoshref="https://en.wikipedia.org/wiki/Unix_shell">shell</a> commands download
1.1Schristosthe latest release's two
1.1Schristos<a href="https://en.wikipedia.org/wiki/Tar_(computing)">tarballs</a>
1.1Schristosto a <abbr>GNU</abbr>/Linux or similar host.</p>
1.2Schristos<pre><code>mkdir tzdb
1.1Schristoscd tzdb
1.1Schristos<a href="https://www.gnu.org/software/wget/">wget</a> https://www.iana.org/time-zones/repository/tzcode-latest.tar.gz
1.1Schristoswget https://www.iana.org/time-zones/repository/tzdata-latest.tar.gz
1.1Schristos<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 -
1.1Schristosgzip -dc tzdata-latest.tar.gz | tar -xf -
1.1Schristos</code></pre>
1.1Schristos<p>Alternatively, the following shell commands download the same
1.1Schristosrelease in a single-tarball format containing extra data
1.1Schristosuseful for regression testing:</p>
1.2Schristos<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>
1.1Schristos<a href="https://www.nongnu.org/lzip/">lzip</a> -dc tzdb-latest.tar.lz | tar -xf -
1.1Schristos</code></pre>
1.1Schristos<p>These commands use convenience links to the latest release
1.1Schristosof the <code><abbr>tz</abbr></code> database hosted by the
1.1Schristos<a href="https://www.iana.org/time-zones">Time Zone Database website</a>
1.1Schristosof the <a href="https://www.iana.org">Internet Assigned Numbers
1.1SchristosAuthority (IANA)</a>.
1.1SchristosOlder releases are in files named
1.1Schristos<code>tzcode<var>V</var>.tar.gz</code>,
1.1Schristos<code>tzdata<var>V</var>.tar.gz</code>, and
1.1Schristos<code>tzdb-<var>V</var>.tar.lz</code>,
1.1Schristoswhere <code><var>V</var></code> is the version.
1.1SchristosSince 1996, each version has been a four-digit year followed by
1.1Schristoslower-case letter (<samp>a</samp> through <samp>z</samp>,
1.1Schristosthen <samp>za</samp> through <samp>zz</samp>, then <samp>zza</samp>
1.1Schristosthrough <samp>zzz</samp>, and so on).
1.1SchristosSince version 2016h, each release has contained a text file named
1.1Schristos"<samp>version</samp>" whose first (and currently only) line is the version.
1.1SchristosThe releases are also available in an
1.1Schristos<a href="ftp://ftp.iana.org/tz/releases/"><abbr
1.1Schristostitle="File Transfer Protocol">FTP</abbr> directory</a> via a
1.1Schristosless-secure protocol.</p>
1.1Schristos<p>Alternatively, a development repository of code and data can be
1.1Schristosretrieved from <a href="https://github.com">GitHub</a> via the shell
1.1Schristoscommand:</p>
1.2Schristos<pre><code><a href="https://git-scm.com">git</a> clone <a href="https://github.com/eggert/tz">https://github.com/eggert/tz</a>
1.1Schristos</code></pre>
1.1Schristos<p>
1.1SchristosSince version 2012e, each release has been tagged in development repositories.
1.1SchristosUntagged commits are less well tested and probably contain
1.1Schristosmore errors.</p>
1.1Schristos<p>
1.1SchristosAfter obtaining the code and data files, see the
1.1Schristos<code>README</code> file for what to do next.
1.1SchristosThe code lets you compile the <code><abbr>tz</abbr></code> source files into
1.2Schristosmachine-readable binary files, one for each location. The binary files
1.2Schristosare in a special timezone information format (<dfn><abbr>TZif</abbr></dfn>).
1.2SchristosThe code also lets
1.2Schristosyou read a <abbr>TZif</abbr> file and interpret timestamps for that
1.1Schristoslocation.</p>
1.1Schristos<h2 id="changes">Changes to the <code><abbr>tz</abbr></code> database</h2>
1.1Schristos<p>
1.1SchristosThe <code><abbr>tz</abbr></code> code and data
1.1Schristosare by no means authoritative. If you find errors, please
1.1Schristossend changes to <a href="mailto:tz@iana.org"><code>tz@iana.org</code></a>,
1.1Schristosthe time zone mailing list. You can also <a
1.1Schristoshref="https://mm.icann.org/mailman/listinfo/tz">subscribe</a> to it
1.1Schristosand browse the <a
1.1Schristoshref="https://mm.icann.org/pipermail/tz/">archive of old
1.1Schristosmessages</a>.</p>
1.1Schristos<p>
1.1SchristosIf your government plans to change its time zone boundaries or
1.1Schristosdaylight saving rules, inform <code>tz@iana.org</code> well in
1.1Schristosadvance, as this will coordinate updates to many cell phones,
1.1Schristoscomputers, and other devices around the world. With
1.1Schristosless than a year's notice there is a good chance that some
1.1Schristoscomputer-based clocks will operate incorrectly after the change, due
1.1Schristosto delays in propagating updates to software and data. The shorter
1.1Schristosthe notice, the more likely clock problems will arise; see "<a
1.1Schristoshref="https://codeofmatt.com/2016/04/23/on-the-timing-of-time-zone-changes/">On
1.1Schristosthe Timing of Time Zone Changes</a>" for examples.
1.1Schristos</p>
1.1Schristos<p>
1.1SchristosChanges to the <code><abbr>tz</abbr></code> code and data are often
1.1Schristospropagated to clients via operating system updates, so
1.1Schristosclient <code><abbr>tz</abbr></code> data can often be corrected by
1.1Schristosapplying these updates. With GNU/Linux and similar systems, if your
1.1Schristosmaintenance provider has not yet adopted the
1.1Schristoslatest <code><abbr>tz</abbr></code> data, you can often short-circuit
1.1Schristosthe process by tailoring the generic instructions in
1.1Schristosthe <code><abbr>tz</abbr> README</code> file and installing the latest
1.1Schristosdata yourself. System-specific instructions for installing the
1.1Schristoslatest <code><abbr>tz</abbr></code> data have also been published
1.1Schristosfor <a href="https://www.ibm.com/developerworks/aix/library/au-aix-olson-time-zone/index.html"><abbr>AIX</abbr></a>,
1.1Schristos<a
1.1Schristoshref="https://play.google.com/store/apps/details?id=com.google.android.timezone.data">Android</a>,
1.1Schristos<a
1.1Schristoshref="http://userguide.icu-project.org/datetime/timezone"><abbr
1.1Schristostitle="International Components for Unicode">ICU</abbr></a>,
1.1Schristos<a href="https://developer.ibm.com/javasdk/support/dst/jtzu/"><abbr>IBM</abbr></a>
1.1Schristosand <a
1.4Schristoshref="https://www.oracle.com/technetwork/java/javase/tzupdater-readme-136440.html">Oracle</a>
1.4SchristosJava, <a href="https://www.joda.org/joda-time/tz_update.html">Joda-Time</a>, <a
1.1Schristoshref="https://dev.mysql.com/doc/refman/en/time-zone-support.html">MySQL</a>,
1.1Schristosand <a
1.1Schristoshref="https://nodatime.org/userguide/tzdb">Noda Time</a> (see below).
1.1Schristos</p>
1.1Schristos<p>Sources for the <code><abbr>tz</abbr></code> database are
1.1Schristos<a href="https://en.wikipedia.org/wiki/UTF-8"><abbr
1.1Schristostitle="Unicode Transformation Format 8-bit">UTF-8</abbr></a>
1.1Schristos<a href="https://en.wikipedia.org/wiki/Text_file">text files</a>
1.1Schristoswith lines terminated by <a href="https://en.wikipedia.org/wiki/Newline"><abbr
1.1Schristostitle="linefeed">LF</abbr></a>,
1.1Schristoswhich can be modified by common text editors such
1.1Schristosas <a href="https://www.gnu.org/software/emacs/">GNU Emacs</a>,
1.1Schristos<a href="https://wiki.gnome.org/Apps/Gedit">gedit</a>, and
1.1Schristos<a href="https://www.vim.org">vim</a>.
1.1SchristosSpecialized source-file editing can be done via the
1.1Schristos<a href="https://packagecontrol.io/packages/zoneinfo">Sublime
1.1Schristoszoneinfo</a> package for <a
1.1Schristoshref="https://www.sublimetext.com">Sublime Text</a> and the <a
1.1Schristoshref="https://marketplace.visualstudio.com/items?itemName=gilmoreorless.vscode-zoneinfo">VSCode
1.1Schristoszoneinfo</a> extension for <a href="https://code.visualstudio.com">Visual
1.1SchristosStudio Code</a>.
1.1Schristos</p>
1.1Schristos<p>
1.1SchristosFor further information about updates, please see
1.1Schristos<a href="https://tools.ietf.org/html/rfc6557">Procedures for
1.1SchristosMaintaining the Time Zone Database</a> (Internet <abbr
1.1Schristostitle="Request For Comments">RFC</abbr> 6557). More detail can be
1.1Schristosfound in <a href="theory.html">Theory and pragmatics of the tz code and data</a>.
1.2Schristos<a href="https://a0.github.io/a0-tzmigration/">A0 TimeZone Migration</a>
1.2Schristosdisplays changes between recent <code><abbr>tzdb</abbr></code> versions.
1.1Schristos</p>
1.1Schristos<h2 id="commentary">Commentary on the <code><abbr>tz</abbr></code> database</h2>
1.1Schristos<ul>
1.1Schristos<li>The article
1.1Schristos<a href="https://en.wikipedia.org/wiki/Tz_database">tz database</a> is
1.1Schristosan encyclopedic summary.</li>
1.1Schristos<li><a href="tz-how-to.html">How to Read the
1.1Schristostz Database Source Files</a> explains the <code><abbr>tz</abbr></code>
1.1Schristosdatabase format.</li>
1.1Schristos<li><a
1.1Schristoshref="https://blog.jonudell.net/2009/10/23/a-literary-appreciation-of-the-olsonzoneinfotz-database/">A
1.1Schristosliterary appreciation of the Olson/Zoneinfo/tz database</a> comments on the
1.1Schristosdatabase's style.</li>
1.1Schristos</ul>
1.1Schristos<h2 id="web">Web sites using recent versions of the
1.1Schristos<code><abbr>tz</abbr></code> database</h2>
1.1Schristos<p>
1.1SchristosThese are listed roughly in ascending order of complexity and fanciness.
1.1Schristos</p>
1.1Schristos<ul>
1.1Schristos<li><a href="https://time.is">Time.is</a> shows locations'
1.1Schristostime and zones.</li>
1.1Schristos<li><a href="https://www.timejones.com">TimeJones.com</a>,
1.1Schristos<a href="https://timezoneconverterapp.com">Time Zone Converter</a> and
1.1Schristos<a href="http://worldclock.com">The World Clock</a>
1.1Schristosare time zone converters.</li>
1.1Schristos<li><a
1.1Schristoshref="http://twiki.org/cgi-bin/xtra/tzdatepick.html">Date and Time Gateway</a>
1.1Schristoslets you see the <code><abbr>TZ</abbr></code> values directly.</li>
1.1Schristos<li><a
1.1Schristoshref="http://www.convertit.com/Go/ConvertIt/World_Time/Current_Time.ASP">Current
1.1SchristosTime in 1000 Places</a> uses descriptions of the values.</li>
1.1Schristos<li><a href="http://www.timezoneconverter.com/cgi-bin/tzc.tzc">Time Zone
1.1SchristosConverter</a>
1.1Schristosuses a pulldown menu.</li>
1.1Schristos<li><a href="http://home.kpn.nl/vanadovv/time/TZworld.html">Complete
1.1Schristostimezone information for all countries</a> displays tables of DST rules.
1.1Schristos<li><a href="https://www.timeanddate.com/worldclock/">The World Clock &ndash;
1.1SchristosWorldwide</a> lets you sort zone names and convert times.</li>
1.1Schristos<li><a href="https://24timezones.com">24TimeZones</a> has a world
1.1Schristostime map and a time converter.</li>
1.1Schristos<li><a href="https://www.zeitverschiebung.net/en/">Time Difference</a>
1.1Schristoscalculates the current time difference between locations.</li>
1.1Schristos<li><a href="http://www.wx-now.com">Weather Now</a> and
1.1Schristos<a href="http://www.thetimenow.com">The Time Now</a> list the weather too.</li>
1.1Schristos</ul>
1.1Schristos<h2 id="protocols">Network protocols for <code><abbr>tz</abbr></code> data</h2>
1.1Schristos<ul>
1.1Schristos<li>The <a href="https://www.ietf.org">Internet Engineering Task Force</a>'s
1.1Schristos<a href="https://datatracker.ietf.org/wg/tzdist/charter/">Time Zone Data
1.1SchristosDistribution Service (tzdist) working group</a> defined <a
1.1Schristoshref="https://tools.ietf.org/html/rfc7808">TZDIST</a>
1.1Schristos(Internet <abbr>RFC</abbr> 7808), a time zone data distribution service,
1.1Schristosalong with <a href="https://tools.ietf.org/html/rfc7809">CalDAV</a>
1.1Schristos(Internet <abbr>RFC</abbr> 7809), a calendar access protocol for
1.2Schristostransferring time zone data by reference.
1.2SchristosThe <a href="https://www.ietf.org/mailman/listinfo/tzdist-bis">tzdist-bis
1.2Schristosmailing list</a> discusses two Internet drafts: <a
1.1Schristosid="TZDIST-Geolocate"
1.2Schristoshref="https://tools.ietf.org/html/draft-murchison-tzdist-geolocate">TZDIST
1.2SchristosGeolocate Extension</a> lets a client determine its timezone
1.1Schristosfrom its geographic location using a <a
1.2Schristoshref="https://tools.ietf.org/html/rfc5870">'geo' URI</a>, and
1.2Schristos<a href="https://tools.ietf.org/html/draft-murchison-tzdist-tzif">The
1.2SchristosTime Zone Information Format (<abbr>TZif</abbr>)</a> specifies the format of
1.2Schristos<abbr>TZif</abbr> data.</li>
1.1Schristos<li>The <a href="https://tools.ietf.org/html/rfc5545">
1.1SchristosInternet Calendaring and Scheduling Core Object Specification
1.1Schristos(iCalendar)</a> (Internet <abbr>RFC</abbr> 5445)
1.1Schristoscovers time zone
1.1Schristosdata; see its VTIMEZONE calendar component.
1.1SchristosThe iCalendar format requires specialized parsers and generators; a
1.1Schristosvariant <a href="https://tools.ietf.org/html/rfc6321">xCal</a>
1.1Schristos(Internet <abbr>RFC</abbr> 6321) uses
1.1Schristos<a href="https://www.w3.org/XML/"><abbr
1.1Schristostitle="Extensible Markup Language">XML</abbr></a> format, and a variant
1.1Schristos<a href="https://tools.ietf.org/html/rfc7265">jCal</a>
1.1Schristos(Internet <abbr>RFC</abbr> 7265)
1.1Schristosuses <a href="https://www.json.org"><abbr
1.1Schristostitle="JavaScript Object Notation">JSON</abbr></a> format.</li>
1.1Schristos</ul>
1.1Schristos<h2 id="compilers">Other <code><abbr>tz</abbr></code> compilers</h2>
1.1Schristos<ul>
1.1Schristos<li><a href="https://sourceforge.net/projects/vzic/">Vzic</a> is a <a
1.1Schristoshref="https://en.wikipedia.org/wiki/C_%28programming_language%29">C</a>
1.1Schristosprogram that compiles
1.1Schristos<code><abbr>tz</abbr></code> source into iCalendar-compatible VTIMEZONE files.
1.1SchristosVzic is freely
1.1Schristosavailable under the <a
1.1Schristoshref="https://www.gnu.org/copyleft/gpl.html"><abbr>GNU</abbr>
1.1SchristosGeneral Public License (<abbr
1.1Schristostitle="General Public License">GPL</abbr>)</a>.</li>
1.1Schristos<li><a href="https://sourceforge.net/projects/tzical/">tziCal &ndash; tz
1.1Schristosdatabase conversion utility</a> is like Vzic, except for the <a
1.1Schristoshref="https://www.microsoft.com/net">.NET framework</a>
1.1Schristosand with a <abbr>BSD</abbr>-style license.</li>
1.1Schristos<li><a
1.4Schristoshref="https://metacpan.org/release/DateTime-TimeZone">DateTime::TimeZone</a>
1.1Schristoscontains a script <code>parse_olson</code> that compiles
1.1Schristos<code><abbr>tz</abbr></code> source into <a href="https://www.perl.org">Perl</a>
1.1Schristosmodules. It is part of the Perl <a
1.4Schristoshref="https://github.com/houseabsolute/DateTime.pm/wiki">DateTime Project</a>,
1.4Schristoswhich is freely
1.1Schristosavailable under both the <abbr>GPL</abbr> and the Perl Artistic
1.1SchristosLicense. DateTime::TimeZone also contains a script
1.1Schristos<code>tests_from_zdump</code> that generates test cases for each clock
1.1Schristostransition in the <code><abbr>tz</abbr></code> database.</li>
1.1Schristos<li>The <a href="https://howardhinnant.github.io/date/tz.html">Time Zone
1.1SchristosDatabase Parser</a> is a
1.1Schristos<a href="https://en.wikipedia.org/wiki/C%2B%2B">C++</a> parser and
1.1Schristosruntime library that is <a
1.1Schristoshref="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0355r4.html">moving
1.1Schristosforward</a> for inclusion in the next iteration of <a
1.1Schristoshref="https://isocpp.org/std/the-standard"><em><abbr
1.1Schristostitle="International Organization for Standardization">ISO</abbr>
1.1SchristosInternational Standard ISO/IEC 14882:2017(E) &ndash; Programming
1.1SchristosLanguage C++</em></a>.
1.1SchristosIt is freely available under the
1.1Schristos<abbr title="Massachusetts Institute of Technology">MIT</abbr> license.</li>
1.1Schristos<li><a id="ICU" href="http://site.icu-project.org">International Components for
1.1SchristosUnicode (<abbr>ICU</abbr>)</a> contains C/C++ and <a
1.1Schristoshref="https://en.wikipedia.org/wiki/Java_%28programming_language%29">Java</a>
1.1Schristoslibraries for internationalization that
1.1Schristoshas a compiler from <code><abbr>tz</abbr></code> source
1.1Schristosand from <abbr title="Common Locale Data Repository">CLDR</abbr> data
1.1Schristos(mentioned <a href="#CLDR">below</a>)
1.1Schristosinto an <abbr>ICU</abbr>-specific format.
1.1Schristos<abbr>ICU</abbr> is freely available under a
1.1Schristos<abbr>BSD</abbr>-style license.</li>
1.1Schristos<li>The <a href="https://github.com/lau/tzdata">Tzdata</a> package for
1.1Schristosthe <a href="https://elixir-lang.org">Elixir</a> language downloads
1.1Schristosand compiles tz source and exposes <abbr
1.1Schristostitle="Application Program Interface">API</abbr>s for use. It is
1.1Schristosfreely available under the <abbr>MIT</abbr> license.</li>
1.1Schristos<li>Java-based compilers and libraries include:
1.1Schristos<ul>
1.1Schristos<li>The <a
1.4Schristoshref="https://www.oracle.com/technetwork/java/javase/tzupdater-readme-136440.html">TZUpdater
1.1Schristostool</a> compiles <code><abbr>tz</abbr></code> source into the format used by
1.1SchristosOracle Java.</li>
1.1Schristos<li>The <a
1.4Schristoshref="https://www.oracle.com/technetwork/articles/java/jf14-date-time-2125367.html">Java
1.4SchristosSE <code>java.time</code> <abbr>API</abbr></a> in Java 8 and later
1.4Schristoscan be supplemented by <a
1.4Schristoshref="https://www.threeten.org/threeten-extra/">ThreeTen-Extra</a>,
1.1Schristoswhich is freely available under a <abbr>BSD</abbr>-style license.</li>
1.4Schristos<li><a href="https://www.joda.org/joda-time/">Joda-Time &ndash; Java date
1.1Schristosand time <abbr>API</abbr></a> contains a class
1.1Schristos<code>org.joda.time.tz.ZoneInfoCompiler</code> that compiles
1.1Schristos<code><abbr>tz</abbr></code> source into a binary format. It inspired
1.1SchristosJava 8 <code>java.time</code>, which its users should migrate to once
1.1Schristosthey can assume Java 8 or later. It is available under the <a
1.1Schristoshref="https://www.apache.org/licenses/LICENSE-2.0">Apache License</a>.</li>
1.4Schristos<li><a href="https://github.com/MenoData/Time4A">Time4A: Advanced date and
1.4Schristostime library for Android</a> and
1.4Schristos<a href="https://github.com/MenoData/Time4J/">Time4J: Advanced date,
1.4Schristostime and interval library for Java</a> compile
1.4Schristos<code><abbr>tz</abbr></code> source into a binary format.
1.4SchristosTime4A is available under the Apache License and Time4J is
1.1Schristosavailable under the <a
1.1Schristoshref="https://www.gnu.org/copyleft/lesser.html"><abbr>GNU</abbr> Lesser
1.1SchristosGeneral Public License (<abbr title="Lesser General Public
1.1SchristosLicense">LGPL</abbr>)</a>.</li>
1.1Schristos<li><abbr>ICU</abbr> (mentioned <a href="#ICU">above</a>) contains compilers and
1.1SchristosJava-based libraries.</li>
1.1Schristos</ul>
1.1Schristos<li><a href="https://nodatime.org">Noda Time &ndash; Date and
1.1Schristostime <abbr>API</abbr> for .NET</a>
1.4Schristosis like Joda-Time and Time4J, but for the .NET framework instead of Java.
1.4SchristosIt is freely available under the Apache License.</li>
1.1Schristos<li><a href="https://en.wikipedia.org/wiki/JavaScript">JavaScript</a>-based
1.1Schristoscompilers and libraries include:
1.1Schristos<ul>
1.1Schristos<li><a
1.1Schristoshref="https://github.com/kshetline/compact-time-zone-generator">CompactTimeZoneGenerator</a>
1.1Schristoscompiles time zone data into a compact form designed for
1.1SchristosJavaScript. It is freely available under a combination of
1.1Schristosthe <abbr>MIT</abbr> license and the Apache License.</li>
1.1Schristos<li><a href="https://momentjs.com/timezone/">Moment Timezone</a> is a
1.1Schristosplugin for the <a href="https://momentjs.com">Moment.js</a> date
1.1Schristosmanipulation library. It is freely available under the <abbr>MIT</abbr>
1.1Schristoslicense.</li>
1.1Schristos<li><a href="https://github.com/mde/timezone-js">TimezoneJS.Date</a>'s
1.1Schristos<abbr>API</abbr> is upward compatible with standard JavaScript
1.1SchristosDates. It is freely available under the Apache License.</li>
1.1Schristos<li><a href="https://github.com/sproutsocial/walltime-js">Walltime-js</a>
1.1Schristostranslates <abbr>UT</abbr> to local time. It is freely available under
1.1Schristosthe <abbr>MIT</abbr> license.</li>
1.1Schristos</ul>
1.1Schristos<li><a href="https://github.com/JuliaTime/">JuliaTime</a> contains a
1.1Schristoscompiler from <code><abbr>tz</abbr></code> source into
1.1Schristos<a href="https://julialang.org/">Julia</a>. It is freely available
1.1Schristosunder the <abbr>MIT</abbr> license.</li>
1.2Schristos<li><a href="https://github.com/pavkam/tzdb">Delphi/<abbr
1.2Schristostitle="Free Pascal Compiler">FPC</abbr> Time Zone Database</a>
1.2Schristoscompiles from <code><abbr>tz</abbr></code> source into
1.2Schristos<a href="https://en.wikipedia.org/wiki/Object_Pascal">Object Pascal</a>
1.2Schristosas compiled by <a href="https://en.wikipedia.org/wiki/Delphi_(IDE)">Delphi</a>
1.2Schristosand <a
1.2Schristoshref="https://en.wikipedia.org/wiki/Free_Pascal"><abbr>FPC</abbr></a>.
1.2SchristosIt is freely available under a <abbr>BSD</abbr>-style license.</li>
1.1Schristos<li><a href="http://pytz.sourceforge.net">pytz &ndash; World Timezone
1.1SchristosDefinitions for Python</a> compiles <code><abbr>tz</abbr></code> source into
1.1Schristos<a href="https://www.python.org">Python</a>.
1.1SchristosIt is freely available under a <abbr>BSD</abbr>-style license.</li>
1.1Schristos<li><a href="https://tzinfo.github.io">TZInfo &ndash;
1.1SchristosRuby Timezone Library</a>
1.1Schristoscompiles <code><abbr>tz</abbr></code> source into
1.1Schristos<a href="https://www.ruby-lang.org/en/">Ruby</a>.
1.1SchristosIt is freely available under the <abbr>MIT</abbr> license.</li>
1.1Schristos<li>The <a href="http://www.squeaksource.com/Chronos/">Chronos Date/Time
1.1SchristosLibrary</a> is
1.1Schristosa <a href="https://en.wikipedia.org/wiki/Smalltalk">Smalltalk</a> class
1.1Schristoslibrary that compiles <code><abbr>tz</abbr></code> source into a time
1.1Schristoszone repository whose format
1.1Schristosis either proprietary or an <abbr>XML</abbr>-encoded
1.1Schristosrepresentation.</li>
1.1Schristos<li><a id="Tcl" href="https://tcl.tk">Tcl</a>
1.1Schristoscontains a developer-oriented parser that compiles <code><abbr>tz</abbr></code>
1.1Schristossource into text files, along with a runtime that can read those
1.1Schristosfiles. Tcl is freely available under a <abbr>BSD</abbr>-style
1.1Schristoslicense.</li>
1.1Schristos</ul>
1.2Schristos<h2 id="TZif">Other <abbr>TZif</abbr> readers</h2>
1.1Schristos<ul>
1.1Schristos<li>The <a
1.1Schristoshref="https://www.gnu.org/software/libc/"><abbr>GNU</abbr> C
1.1SchristosLibrary</a>
1.1Schristoshas an independent, thread-safe implementation of
1.2Schristosa <abbr>TZif</abbr> file reader.
1.1SchristosThis library is freely available under the LGPL
1.1Schristosand is widely used in <abbr>GNU</abbr>/Linux systems.</li>
1.1Schristos<li><a href="https://www.gnome.org">GNOME</a>'s
1.1Schristos<a href="https://developer.gnome.org/glib/">GLib</a> has
1.2Schristosa <abbr>TZif</abbr> file reader written in C that
1.1Schristoscreates a <code>GTimeZone</code> object representing sets
1.1Schristosof <abbr>UT</abbr> offsets.
1.1SchristosIt is freely available under the <abbr>LGPL</abbr>.</li>
1.1Schristos<li>The
1.1Schristos<a href="https://github.com/bloomberg/bde/wiki">BDE Standard Library</a>'s
1.1Schristos<code>baltzo::TimeZoneUtil</code> component contains a C++
1.2Schristosimplementation of a <abbr>TZif</abbr> file reader. It is freely available under
1.1Schristosthe Apache License.</li>
1.1Schristos<li><a href="https://github.com/google/cctz">CCTZ</a> is a simple C++
1.1Schristoslibrary that translates between <abbr>UT</abbr> and civil time and
1.2Schristoscan read <abbr>TZif</abbr> files. It is freely available under the Apache
1.1SchristosLicense.</li>
1.1Schristos<li><a href="http://bmsi.com/java/#TZ">ZoneInfo.java</a>
1.2Schristosis a <abbr>TZif</abbr> file reader written in Java.
1.1SchristosIt is freely available under the <abbr>LGPL</abbr>.</li>
1.1Schristos<li><a href="https://github.com/derickr/timelib">Timelib</a> is a C
1.2Schristoslibrary that reads <abbr>TZif</abbr> files and converts
1.2Schristostimestamps from one time zone or format to another.
1.1SchristosIt is used by <a href="https://secure.php.net"><abbr
1.1Schristostitle="PHP: Hypertext Preprocessor">PHP</abbr></a>,
1.1Schristos<a href="https://hhvm.com"><abbr title="HipHop Virtual Machine">HHVM</abbr></a>,
1.1Schristosand <a href="https://www.mongodb.com">MongoDB</a>.
1.1SchristosIt is freely available under the <abbr>MIT</abbr> license.</li>
1.1Schristos<li><a href="https://github.com/bigeasy/timezone">Timezone</a> is a
1.1SchristosJavaScript library that supports date arithmetic that is time zone
1.1Schristosaware. It is freely available under the <abbr>MIT</abbr> license.</li>
1.1Schristos<li>Tcl, mentioned <a href="#Tcl">above</a>, also contains a
1.2Schristos<abbr>TZif</abbr> file reader.</li>
1.4Schristos<li><a href="https://metacpan.org/pod/DateTime::TimeZone::Tzfile">
1.1SchristosDateTime::TimeZone::Tzfile</a>
1.2Schristosis a <abbr>TZif</abbr> file reader written in Perl.
1.1SchristosIt is freely available under the same terms as Perl
1.1Schristos(dual <abbr>GPL</abbr> and Artistic license).</li>
1.1Schristos<li>The
1.1Schristospublic-domain <a href="https://github.com/dbaron/tz.js">tz.js</a>
1.1Schristoslibrary contains a Python tool that
1.2Schristosconverts <abbr>TZif</abbr> data into
1.1Schristos<abbr>JSON</abbr>-format data suitable for use
1.1Schristosin its JavaScript library for time zone conversion. Dates before 1970
1.1Schristosare not supported.</li>
1.1Schristos<li>The <a
1.1Schristoshref="https://hackage.haskell.org/package/timezone-olson">timezone-olson</a>
1.1Schristospackage contains <a href="https://www.haskell.org">Haskell</a> code that
1.2Schristosparses and uses <abbr>TZif</abbr> data. It is freely
1.1Schristosavailable under a <abbr>BSD</abbr>-style license.</li>
1.1Schristos</ul>
1.1Schristos<h2 id="software">Other <code><abbr>tz</abbr></code>-based time zone software</h2>
1.1Schristos<ul>
1.1Schristos<li><a href="https://foxclocks.org">FoxClocks</a>
1.1Schristosis an extension for <a href="https://www.google.com/chrome/">Google
1.1SchristosChrome</a> and for <a
1.1Schristoshref="https://developer.mozilla.org/en-US/docs/Mozilla/Tech/Toolkit_API">Mozilla
1.1SchristosToolkit</a> applications like <a
1.1Schristoshref="https://www.mozilla.org/en-US/firefox/new/">Firefox</a> and <a
1.1Schristoshref="https://www.mozilla.org/en-US/thunderbird/">Thunderbird</a>.
1.1SchristosIt displays multiple clocks in the application window, and has a mapping
1.1Schristosinterface to <a href="https://www.google.com/earth/">Google Earth</a>.
1.1SchristosIt is freely available under the <abbr>GPL</abbr>.</li>
1.1Schristos<li><a href="https://golang.org">Go programming language</a>
1.1Schristosimplementations contain a copy of a 32-bit subset of a recent
1.1Schristos<code><abbr>tz</abbr></code> database in a
1.1SchristosGo-specific format.</li>
1.1Schristos<li><a
1.1Schristoshref="http://users.skynet.be/Peter.Verthez/projects/intclock/">International
1.1Schristosclock (intclock)</a> is a clock that displays multiple time zones on
1.1Schristos<abbr>GNU</abbr>/Linux and similar systems. It is freely available
1.1Schristosunder the <abbr>GPL</abbr>.</li>
1.1Schristos<li>Microsoft Windows 8.1
1.1Schristosand later has <code><abbr>tz</abbr></code> data and <abbr>CLDR</abbr>
1.3Schristosdata (mentioned <a href="#CLDR">below</a>) used by the
1.3Schristos<a href="https://en.wikipedia.org/wiki/Windows_Runtime">Windows Runtime</a> /
1.3Schristos<a href="https://en.wikipedia.org/wiki/Universal_Windows_Platform">Universal Windows Platform</a> classes
1.3Schristos<a href="https://docs.microsoft.com/uwp/api/Windows.Globalization.DateTimeFormatting.DateTimeFormatter"><code>DateTimeFormatter</code></a> and
1.3Schristos<a href="https://docs.microsoft.com/uwp/api/windows.globalization.calendar"><code>Calendar</code></a>.
1.1Schristos<a id="System.TimeZoneInfo"
1.1Schristoshref="https://blogs.msdn.microsoft.com/bclteam/2007/06/07/exploring-windows-time-zones-with-system-timezoneinfo-josh-free/">Exploring
1.1SchristosWindows Time Zones with <code>System.TimeZoneInfo</code></a> describes
1.1Schristosthe older, proprietary method of Microsoft Windows 2000 and later,
1.1Schristoswhich stores time zone data in the
1.1Schristos<a href="https://en.wikipedia.org/wiki/Windows_Registry">Windows Registry</a>. The
1.1Schristos<a
1.1Schristoshref="https://unicode.org/cldr/charts/latest/supplemental/zone_tzid.html">Zone &rarr;
1.1SchristosTzid table</a> or <a
1.1Schristoshref="https://unicode.org/repos/cldr/trunk/common/supplemental/windowsZones.xml"><abbr>XML</abbr>
1.1Schristosfile</a> of the <abbr>CLDR</abbr> data maps proprietary zone IDs
1.1Schristosto <code><abbr>tz</abbr></code> names.
1.3SchristosThese mappings can be performed programmatically via the <a href="https://github.com/mj1856/TimeZoneConverter">TimeZoneConverter</a> .NET library,
1.3Schristosor the ICU Java and C++ libraries mentioned <a href="#ICU">above</a>.
1.1Schristos<li><a
1.1Schristoshref="https://www.oracle.com/java/index.html">Oracle
1.1SchristosJava</a> contains a copy of a subset of a recent
1.1Schristos<code><abbr>tz</abbr></code> database in a
1.1SchristosJava-specific format.</li>
1.2Schristos<li><a href="https://relativedata.com/page/Time-Zone-Master">Time Zone
1.1SchristosMaster</a> is a Microsoft Windows clock program that can automatically
1.4Schristosdownload, compile and use <code><abbr>tz</abbr></code> releases.
1.4SchristosThe Basic version is free.</li>
1.1Schristos<li><a
1.1Schristoshref="http://veladg.com/velaterra.html">VelaTerra</a> is
1.1Schristosa macOS program. Its developers
1.1Schristos<a href="http://veladg.com/tzoffer.html">offer free
1.1Schristoslicenses</a> to <code><abbr>tz</abbr></code> contributors.</li>
1.1Schristos</ul>
1.1Schristos<h2 id="other-dbs">Other time zone databases</h2>
1.1Schristos<ul>
1.1Schristos<li><a href="https://www.astro.com/atlas">Time-zone Atlas</a>
1.4Schristosis Astrodienst's Web version of Shanks and Pottenger's out-of-print
1.4Schristostime zone history atlases
1.4Schristos<a href="https://www.worldcat.org/oclc/468828649">for the US</a> and
1.4Schristos<a href="https://www.worldcat.org/oclc/76950459">for the world</a>,
1.4Schristosnow published in <a
1.1Schristoshref="https://astrocom.com/astrology-products/software/acs-atlas-software">software</a>
1.1Schristosform by <a href="https://astrocom.com">ACS-Starcrafts</a>.
1.4SchristosAlthough these extensive atlases
1.4Schristos<a href="https://astrologynewsservice.com/opinion/how-astrologers-contributed-to-the-information-age-a-brief-history-of-time/">were
1.4Schristossources for much of the older <code><abbr>tz</abbr></code> data</a>,
1.4Schristosthey are unreliable as Shanks appears to have
1.1Schristosguessed many <abbr>UT</abbr> offsets and transitions. The atlases cite no
1.1Schristossources and do not indicate which entries are guesswork.</li>
1.1Schristos<li><a href="https://en.wikipedia.org/wiki/HP-UX">HP-UX</a> has a database in
1.1Schristosits own <code>tztab</code>(4) format.</li>
1.1Schristos<li>Microsoft Windows has proprietary data mentioned
1.1Schristos<a href="#System.TimeZoneInfo">above</a>.</li>
1.1Schristos<li><a href="https://www.worldtimeserver.com">World Time Server</a>
1.1Schristosis another time zone database.</li>
1.1Schristos<li>The <a
1.1Schristoshref="https://www.iata.org/publications/store/Pages/standard-schedules-information.aspx">Standard
1.1SchristosSchedules Information Manual</a> of the
1.1SchristosInternational Air Transport Association
1.1Schristosgives current time zone rules for airports served by commercial aviation.</li>
1.1Schristos</ul>
1.1Schristos<h2 id="maps">Maps</h2>
1.1Schristos<ul>
1.1Schristos<li>The <a href="https://www.cia.gov/index.html">United States Central
1.1SchristosIntelligence Agency (<abbr
1.1Schristostitle="Central Intelligence Agency">CIA</abbr>)</a> publishes a <a
1.1Schristoshref="https://www.cia.gov/library/publications/the-world-factbook/graphics/ref_maps/physical/pdf/standard_time_zones_of_the_world.pdf">time
1.1Schristoszone map</a>; the
1.1Schristos<a
1.1Schristoshref="https://www.lib.utexas.edu/maps/world.html">Perry&ndash;Casta&ntilde;eda
1.1SchristosLibrary Map Collection</a>
1.1Schristosof the University of Texas at Austin has copies of
1.1Schristosrecent editions.
1.1SchristosThe pictorial quality is good,
1.1Schristosbut the maps do not indicate daylight saving time,
1.1Schristosand parts of the data are a few years out of date.</li>
1.1Schristos<li><a href="https://www.worldtimezone.com">Current time around the world
1.1Schristosand standard time zones map of the world</a>
1.1Schristoshas several fancy time zone maps; it covers Russia particularly well.
1.1SchristosThe maps' pictorial quality is not quite as good as the
1.1Schristos<abbr>CIA</abbr>'s
1.1Schristosbut the maps are more up to date.</li>
1.1Schristos<li><a
1.1Schristoshref="https://blog.poormansmath.net/how-much-is-time-wrong-around-the-world/">How
1.1Schristosmuch is time wrong around the world?</a> maps the difference between
1.1Schristosmean solar and standard time, highlighting areas such as western China
1.1Schristoswhere the two differ greatly. It's a bit out of date, unfortunately.</li>
1.1Schristos</ul>
1.1Schristos<h2 id="boundaries">Time zone boundaries</h2>
1.2Schristos<p>Geographical boundaries between timezones are available
1.1Schristosfrom several <a href="https://en.wikipedia.org/wiki/Geolocation">geolocation</a>
1.1Schristosservices and other sources.</p>
1.1Schristos<ul>
1.1Schristos<li><a href="https://github.com/evansiroky/timezone-boundary-builder">Timezone
1.1SchristosBoundary Builder</a> extracts
1.1Schristos<a href="https://www.openstreetmap.org">Open Street Map</a> data to build
1.2Schristosboundaries of <code><abbr>tzdb</abbr></code> timezones.
1.1SchristosIts code is freely available under the <abbr>MIT</abbr> license, and
1.1Schristosits data entries are freely available under the
1.1Schristos<a href="https://opendatacommons.org/licenses/odbl/">Open Data Commons
1.1SchristosOpen Database License</a>. The maps' borders appear to be quite accurate.</li>
1.1Schristos<li>Programmatic interfaces that map geographical coordinates via tz_world to
1.2Schristos<code><abbr>tzdb</abbr></code> timezones include:
1.1Schristos<ul>
1.1Schristos<li><a href="https://github.com/mj1856/GeoTimeZone">GeoTimeZone</a> is
1.1Schristoswritten in <a
1.1Schristoshref="https://en.wikipedia.org/wiki/C_Sharp_(programming_language)">C#</a>
1.1Schristosand is freely available under the <abbr>MIT</abbr> license.</li>
1.1Schristos<li>The <a href="https://github.com/bradfitz/latlong">latlong package</a>
1.1Schristosis written in Go and is freely available under the Apache License.</li>
1.1Schristos<li><a href="https://github.com/drtimcooper/LatLongToTimezone">LatLongToTimezone</a>,
1.1Schristosin both Java and
1.1Schristos<a href="https://en.wikipedia.org/wiki/Swift_(programming_language)">Swift</a>
1.1Schristosform, is freely available under the MIT license.</li>
1.1Schristos<li>For <a href="https://nodejs.org/en/">Node.js</a>,
1.1Schristosthe <a href="https://www.npmjs.com/package/geo-tz">geo-tz module</a>
1.1Schristosis freely available under the MIT license, and
1.1Schristosthe <a href="https://www.npmjs.com/package/tz-lookup">tz-lookup module</a>
1.1Schristosis in the public domain.</li>
1.1Schristos<li>The <a
1.1Schristoshref="https://github.com/MrMinimal64/timezonefinder">timezonefinder</a>
1.1Schristoslibrary for Python is freely available under the MIT license.
1.1Schristos<li>The <a
1.1Schristoshref="https://github.com/gunyarakun/timezone_finder">timezone_finder</a>
1.1Schristoslibrary for Ruby is freely available under the MIT license.</li>
1.1Schristos</ul></li>
1.1Schristos<li>Free access via a network API, if you register a key, is provided by
1.4Schristosthe <a
1.4Schristoshref="https://www.geonames.org/export/web-services.html#timezone">GeoNames
1.4SchristosTimezone web service</a>, the <a
1.4Schristoshref="https://developers.google.com/maps/documentation/timezone/intro">Google
1.4SchristosMaps Time Zone API</a>, and
1.1Schristosthe <a href="https://timezonedb.com">Time Zone Database &amp; API</a>.
1.1SchristosCommercial network API access is provided
1.1Schristosby <a href="https://askgeo.com">AskGeo</a>
1.1Schristosand <a href="https://www.geogarage.com/blog/news-1/post/geogarage-time-zone-api-31">GeoGarage</a>.
1.1Schristos</li>
1.1Schristos<li>"<a
1.1Schristoshref="https://stackoverflow.com/questions/16086962/how-to-get-a-time-zone-from-a-location-using-latitude-and-longitude-coordinates/16086964">How
1.1Schristosto get a time zone from a location using latitude and longitude
1.1Schristoscoordinates?</a>" discusses other geolocation possibilities.</li>
1.1Schristos<li><a href="http://statoids.com/statoids.html">Administrative
1.1SchristosDivisions of Countries ("Statoids")</a> lists
1.1Schristospolitical subdivision data related to time zones.</li>
1.1Schristos<li><a href="http://home.kpn.nl/vanadovv/time/Multizones.html">Time
1.1Schristoszone boundaries for multizone countries</a> summarizes legal
1.1Schristosboundaries between time zones within countries.</li>
1.1Schristos<li><a href="http://manifold.net/info/freestuff.shtml">Manifold Software
1.1Schristos&ndash; GIS and Database Tools</a> includes a Manifold-format map of
1.1Schristosworld time zone boundaries distributed under the
1.1Schristos<abbr>GPL</abbr>.</li>
1.1Schristos<li>A ship within the <a
1.1Schristoshref="https://en.wikipedia.org/wiki/Territorial_waters">territorial
1.1Schristoswaters</a> of any nation uses that nation's time. In international
1.1Schristoswaters, time zone boundaries are meridians 15&deg; apart, except that
1.1Schristos<abbr>UT</abbr>&minus;12 and <abbr>UT</abbr>+12 are each 7.5&deg;
1.1Schristoswide and are separated by
1.1Schristosthe 180&deg; meridian (not by the International Date Line, which is
1.1Schristosfor land and territorial waters only). A captain can change ship's
1.1Schristosclocks any time after entering a new time zone; midnight changes are
1.1Schristoscommon.</li>
1.1Schristos</ul>
1.1Schristos<h2 id="civil">Civil time concepts and history</h2>
1.1Schristos<ul>
1.1Schristos<li><a href="https://www.nist.gov/pml/time-and-frequency-division/popular-links/walk-through-time">A
1.1SchristosWalk through Time</a>
1.1Schristossurveys the evolution of timekeeping.</li>
1.4Schristos<li>The history of daylight saving time is surveyed in <a
1.4Schristoshref="http://www.webexhibits.org/daylightsaving/">About Daylight
1.4SchristosSaving Time &ndash; History, rationale, laws &amp; dates</a> and summarized in
1.4Schristos<a href="http://seizethedaylight.com/dst/">A Brief
1.4SchristosHistory of Daylight Saving Time</a>.</li>
1.4Schristos<li><a href="https://www.laphamsquarterly.org/roundtable/time-lords">Time
1.4SchristosLords</a> discusses how authoritarians manipulate civil time.</li>
1.1Schristos<li><a href="https://www.w3.org/TR/timezone/">Working with Time Zones</a>
1.1Schristoscontains guidelines and best practices for software applications that
1.1Schristosdeal with civil time.</li>
1.1Schristos<li><a href="https://www.staff.science.uu.nl/~gent0113/idl/idl.htm">A History of
1.1Schristosthe International Date Line</a> tells the story of the most important
1.1Schristostime zone boundary.</li>
1.1Schristos<li><a href="http://statoids.com/tconcept.html">Basic Time
1.1SchristosZone Concepts</a> discusses terminological issues behind time zones.</li>
1.1Schristos</ul>
1.1Schristos<h2 id="national">National histories of legal time</h2>
1.1Schristos<dl>
1.1Schristos<dt>Australia</dt>
1.1Schristos<dd>The Parliamentary Library has commissioned a <a
1.1Schristoshref="https://www.aph.gov.au/binaries/library/pubs/rp/2009-10/10rp10.pdf">research
1.1Schristospaper on daylight saving time in Australia</a>.
1.1SchristosThe Bureau of Meteorology publishes a list of <a
1.1Schristoshref="http://www.bom.gov.au/climate/averages/tables/dst_times.shtml">Implementation
1.1SchristosDates of Daylight Savings Time within Australia</a>.</dd>
1.1Schristos<dt>Belgium</dt>
1.1Schristos<dd>The Royal Observatory of Belgium maintains a table of <a
1.4Schristoshref="https://www.astro.oma.be/GENERAL/INFO/nli001a.html"
1.1Schristoshreflang="nl">time in Belgium (in Dutch)</a>.</dd>
1.1Schristos<dt>Brazil</dt>
1.1Schristos<dd>The Time Service Department of the National Observatory
1.1Schristosrecords <a href="http://pcdsh01.on.br/DecHV.html"
1.1Schristoshreflang="pt-BR">Brazil's daylight saving time decrees (in
1.1SchristosPortuguese)</a>.</dd>
1.1Schristos<dt>Canada</dt>
1.1Schristos<dd>National Research Council Canada publishes current
1.1Schristosand some older information about <a
1.1Schristoshref="https://www.nrc-cnrc.gc.ca/eng/services/time/time_zones.html">time
1.1Schristoszones &amp; daylight saving time</a>.</dd>
1.1Schristos<dt>Chile</dt>
1.1Schristos<dd>The Hydrographic and Oceanographic Service of the Chilean Navy publishes a
1.4Schristos<a href="https://www.horaoficial.cl/historia_hora.html" hreflang="es">history of
1.1SchristosChile's official time (in Spanish)</a>.</dd>
1.3Schristos<dt>China</dt>
1.3Schristos<dd>The Hong Kong Observatory maintains a
1.3Schristos<a href="https://www.hko.gov.hk/gts/time/Summertime.htm">history of
1.3Schristos summer time in Hong Kong</a>,
1.3Schristosand Macau's Meteorological and Geophysical Bureau maintains a <a
1.3Schristoshref="http://www.smg.gov.mo/smg/geophysics/e_t_Summer%20Time.htm">similar
1.3Schristoshistory for Macau</a>.
1.3SchristosUnfortunately the latter is incomplete and has errors.</dd>
1.1Schristos<dt>Czech Republic</dt>
1.1Schristos<dd><a href="https://kalendar.beda.cz/kdy-zacina-a-konci-letni-cas"
1.1Schristoshreflang="cs">When daylight saving time starts and ends (in Czech)</a>
1.1Schristossummarizes and cites historical DST regulations.</dd>
1.1Schristos<dt>Germany</dt>
1.1Schristos<dd>The National Institute for Science and Technology maintains the <a
1.1Schristoshref="https://www.ptb.de/cms/en/fachabteilungen/abt4/fb-44/ag-441/realisation-of-legal-time-in-germany.html">Realisation
1.1Schristosof Legal Time in Germany</a>.</dd>
1.1Schristos<dt>Israel</dt>
1.1Schristos<dd>The Interior Ministry periodically issues <a
1.1Schristoshref="ftp://ftp.cs.huji.ac.il/pub/tz/announcements"
1.1Schristoshreflang="he">announcements (in Hebrew)</a>.</dd>
1.1Schristos<dt>Italy</dt>
1.1Schristos<dd>The National Institute of Metrological Research maintains a
1.4Schristos<a href="http://oldsite.inrim.it/res/tf/ora_legale_i.shtml" hreflang="it">table
1.4Schristosof civil time (in Italian)</a>.</dd>
1.2Schristos<dt>Malaysia</dt>
1.2Schristos<dd>See Singapore <a href="#Singapore">below</a>.</dd>
1.1Schristos<dt>Mexico</dt>
1.1Schristos<dd>The Investigation and Analysis Service of the Mexican Library of
1.1SchristosCongress has published a <a
1.1Schristoshref="http://www.diputados.gob.mx/bibliot/publica/inveyana/polisoc/horver/index.htm"
1.1Schristoshreflang="es">history of Mexican local time (in Spanish)</a>.</dd>
1.1Schristos<dt>Netherlands</dt>
1.1Schristos<dd><a href="https://www.staff.science.uu.nl/~gent0113/wettijd/wettijd.htm"
1.1Schristoshreflang="nl">Legal time in the Netherlands (in Dutch)</a>
1.1Schristoscovers the history of local time in the Netherlands from ancient times.</dd>
1.1Schristos<dt>New Zealand</dt>
1.1Schristos<dd>The Department of Internal Affairs maintains a brief <a
1.1Schristoshref="https://www.dia.govt.nz/Daylight-Saving-History">History of
1.1SchristosDaylight Saving</a>. The privately-maintained <a
1.1Schristoshref="http://astrologyschool.com/nztime.html">History of New Zealand
1.1Schristostime</a> has more details.</dd>
1.1Schristos<dt>Singapore</dt>
1.1Schristos<dd><a id="Singapore"
1.1Schristoshref="http://www.math.nus.edu.sg/aslaksen/teaching/timezone.html">Why
1.1Schristosis Singapore in the "Wrong" Time Zone?</a> details the
1.1Schristoshistory of legal time in Singapore and Malaysia.</dd>
1.1Schristos<dt>United Kingdom</dt>
1.1Schristos<dd><a
1.1Schristoshref="https://www.polyomino.org.uk/british-time/">History of
1.1Schristoslegal time in Britain</a> discusses in detail the country
1.1Schristoswith perhaps the best-documented history of clock adjustments.
1.1SchristosThe National Physical Laboratory also maintains an <a
1.1Schristoshref="http://www.npl.co.uk/educate-explore/what-is-time/archive-of-summer-time-dates">Archive
1.1Schristosof Summer time dates</a>.</dd>
1.1Schristos<dt>United States</dt>
1.1Schristos<dd>The Department of Transportation's <a
1.1Schristoshref="https://www.transportation.gov/regulations/recent-time-zone-proceedings">Recent
1.1SchristosTime Zone Proceedings</a> lists changes to time zone boundaries.</dd>
1.1Schristos<dt>Uruguay</dt>
1.1Schristos<dd>The Oceanography, Hydrography, and Meteorology Service of the Uruguayan
1.1SchristosNavy (SOHMA) publishes an annual <a
1.1Schristoshref="http://www.armada.mil.uy/Pagina/institucion/dimat/sohma/almanaque.html" hreflang="es">almanac
1.1Schristos(in Spanish)</a>.</dd>
1.1Schristos</dl>
1.1Schristos<h2 id="precision">Precision timekeeping</h2>
1.1Schristos<ul>
1.1Schristos<li><a
1.1Schristoshref="http://leapsecond.com/hpan/an1289.pdf">The
1.1SchristosScience of Timekeeping</a> is a thorough introduction
1.1Schristosto the theory and practice of precision timekeeping.</li>
1.1Schristos<li><a href="https://doi.org/10.1007/978-3-319-59909-0">The Science of
1.1SchristosTime 2016</a> contains several freely-readable papers.</li>
1.1Schristos<li><a href="http://www.ntp.org"><abbr
1.1Schristostitle="Network Time Protocol">NTP</abbr>: The Network
1.1SchristosTime Protocol</a> (Internet <abbr>RFC</abbr> 5905)
1.1Schristosdiscusses how to synchronize clocks of
1.1SchristosInternet hosts.</li>
1.2Schristos<li>The <a href="https://www.usenix.org/system/files/conference/nsdi18/nsdi18-geng.pdf"><span style="font-variant: small-caps">Huygens</span></a>
1.2Schristosfamily of software algorithms can achieve accuracy to a few tens of
1.2Schristosnanoseconds in scalable server farms without special hardware.</li>
1.1Schristos<li>The <a
1.1Schristoshref="https://www.nist.gov/intelligent-systems-division/ieee-1588">Precision
1.1SchristosTime Protocol</a> (<abbr
1.1Schristostitle="Institute of Electrical and Electronics Engineers">IEEE</abbr> 1588)
1.2Schristoscan achieve submicrosecond clock accuracy on a local area network
1.2Schristoswith special-purpose hardware.</li>
1.1Schristos<li><a
1.1Schristoshref="https://tools.ietf.org/html/rfc4833">Timezone
1.1SchristosOptions for <abbr title="Dynamic Host Configuration Protocol">DHCP</abbr></a>
1.1Schristos(Internet <abbr>RFC</abbr> 4833)
1.1Schristosspecifies a <a
1.1Schristoshref="https://en.wikipedia.org/wiki/Dynamic_Host_Configuration_Protocol"><abbr>DHCP</abbr></a>
1.1Schristosoption for a server to configure
1.1Schristosa client's time zone and daylight saving settings automatically.</li>
1.1Schristos<li><a
1.1Schristoshref="https://www.cv.nrao.edu/~rfisher/Ephemerides/times.html">Astronomical
1.1SchristosTimes</a> explains more abstruse astronomical time scales like
1.1Schristos<abbr title="Terrestrial Dynamic Time">TDT</abbr>,
1.1Schristos<abbr title="Geocentric Coordinate Time">TCG</abbr>, and
1.1Schristos<abbr title="Barycentric Dynamic Time">TDB</abbr>.
1.1Schristos<a href="https://www.ucolick.org/~sla/leapsecs/timescales.html">Time
1.1SchristosScales</a> goes into more detail, particularly for historical variants.</li>
1.1Schristos<li>The <a href="https://www.iau.org"><abbr
1.1Schristostitle="International Astronomical Union">IAU</abbr></a>'s <a
1.1Schristoshref="http://www.iausofa.org"><abbr
1.1Schristostitle="Standards Of Fundamental Astronomy">SOFA</abbr></a>
1.1Schristoscollection contains C and <a
1.1Schristoshref="https://en.wikipedia.org/wiki/Fortran">Fortran</a>
1.1Schristoscode for converting among time scales like
1.1Schristos<abbr title="International Atomic Time">TAI</abbr>,
1.1Schristos<abbr>TDB</abbr>, <abbr>TDT</abbr> and
1.1Schristos<abbr>UTC</abbr>.</li>
1.1Schristos<li><a
1.1Schristoshref="https://www.giss.nasa.gov/tools/mars24/help/notes.html">Mars24 Sunclock
1.1Schristos&ndash; Time on Mars</a> describes Airy Mean Time (<abbr>AMT</abbr>) and the
1.1Schristosdiverse local time
1.1Schristosscales used by each landed mission on Mars.</li>
1.1Schristos<li><a href="http://leapsecond.com">LeapSecond.com</a> is
1.1Schristosdedicated not only to leap seconds but to precise time and frequency
1.1Schristosin general. It covers the state of the art in amateur timekeeping, and
1.1Schristoshow the art has progressed over the past few decades.</li>
1.1Schristos<li><a
1.1Schristoshref="https://www.iers.org/IERS/EN/Publications/Bulletins/bulletins.html"><abbr
1.1Schristostitle="International Earth Rotation and Reference Systems Service">IERS</abbr>
1.1SchristosBulletins</a> contains official publications of the International
1.1SchristosEarth Rotation and Reference Systems Service, which decides when leap
1.4Schristosseconds occur. The <code><abbr>tz</abbr></code> code and data support leap seconds
1.1Schristosvia an optional "<code>right</code>" configuration, as opposed to the
1.1Schristosdefault "<code>posix</code>" configuration.</li>
1.1Schristos<li><a href="https://developers.google.com/time/smear">Leap Smear</a>
1.1Schristosdiscusses how to gradually adjust <abbr>POSIX</abbr> clocks near a
1.1Schristosleap second so that they disagree with <abbr>UTC</abbr> by at most a
1.1Schristoshalf second, even though every <abbr>POSIX</abbr> minute has exactly
1.4Schristossixty seconds. This approach works with the default <code><abbr>tz</abbr></code>
1.1Schristos"<code>posix</code>" configuration, is <a
1.1Schristoshref="http://bk1.ntp.org/ntp-stable/README.leapsmear">supported</a> by
1.1Schristosthe <abbr>NTP</abbr> reference implementation, and is used by major
1.1Schristoscloud service providers.</li>
1.1Schristos<li>The <a
1.1Schristoshref="https://pairlist6.pair.net/mailman/listinfo/leapsecs">Leap
1.1SchristosSecond Discussion List</a> covers <a
1.1Schristoshref="https://www2.unb.ca/gge/Resources/gpsworld.november99.pdf">McCarthy
1.1Schristosand Klepczynski's 1999 proposal to discontinue leap seconds</a>,
1.1Schristosdiscussed further in
1.1Schristos<a href="https://www.cl.cam.ac.uk/~mgk25/time/metrologia-leapsecond.pdf">The
1.1Schristosleap second: its history and possible future</a>.
1.1Schristos<a href="https://www.ucolick.org/~sla/leapsecs/"><abbr>UTC</abbr>
1.1Schristosmight be redefined
1.1Schristoswithout Leap Seconds</a> gives pointers on this
1.1Schristoscontentious issue, which was active until 2015 and could become active
1.1Schristosagain.</li>
1.1Schristos</ul>
1.1Schristos<h2 id="notation">Time notation</h2>
1.1Schristos<ul>
1.1Schristos<li>The <a id="CLDR" href="http://cldr.unicode.org">Unicode Common Locale Data
1.1SchristosRepository (<abbr>CLDR</abbr>) Project</a> has localizations for time
1.1Schristoszone names, abbreviations, identifiers, and formats. For example, it
1.1Schristoscontains French translations for "Eastern European Summer Time",
1.1Schristos"<abbr title="Eastern European Summer Time">EEST</abbr>", and
1.1Schristos"Bucharest". Its
1.1Schristos<a href="https://unicode.org/cldr/charts/latest/by_type/">by-type
1.1Schristoscharts</a> show these values for many locales. Data values are available in
1.1Schristosboth <abbr title="Locale Data Markup Language">LDML</abbr>
1.1Schristos(an <abbr>XML</abbr> format) and <abbr>JSON</abbr>.
1.1Schristos<li>
1.1Schristos<a href="https://www.cl.cam.ac.uk/~mgk25/iso-time.html">A summary of
1.1Schristosthe international standard date and time notation</a> is a good
1.1Schristossummary of
1.1Schristos<a
1.1Schristoshref="https://www.iso.org/standard/40874.html"><em><abbr>ISO</abbr>
1.1Schristos8601:2004 &ndash; Data elements and interchange formats &ndash; Information
1.1Schristosinterchange &ndash; Representation of dates and times</em></a>.</li>
1.1Schristos<li>
1.1Schristos<a href="https://www.w3.org/TR/xmlschema-2/#dateTime"><abbr>XML</abbr>
1.1SchristosSchema: Datatypes &ndash; dateTime</a> specifies a format inspired by
1.1Schristos<abbr>ISO</abbr> 8601 that is in common use in <abbr>XML</abbr> data.</li>
1.1Schristos<li><a href="https://tools.ietf.org/html/rfc5322#section-3.3">&sect;3.3 of
1.1SchristosInternet Message Format</a> (Internet <abbr>RFC</abbr> 5322)
1.1Schristosspecifies the time notation used in email and <a
1.1Schristoshref="https://en.wikipedia.org/wiki/Hypertext_Transfer_Protocol"><abbr>HTTP</abbr></a>
1.1Schristosheaders.</li>
1.1Schristos<li>
1.1Schristos<a href="https://tools.ietf.org/html/rfc3339">Date and Time
1.1Schristoson the Internet: Timestamps</a> (Internet <abbr>RFC</abbr> 3339)
1.1Schristosspecifies an <abbr>ISO</abbr> 8601
1.1Schristosprofile for use in new Internet
1.1Schristosprotocols.</li>
1.1Schristos<li>
1.1Schristos<a href="https://www.hackcraft.net/web/datetime/">Date &amp; Time
1.1SchristosFormats on the Web</a> surveys web- and Internet-oriented date and time
1.1Schristosformats.</li>
1.1Schristos<li>Alphabetic time zone abbreviations should not be used as unique
1.1Schristosidentifiers for <abbr>UT</abbr> offsets as they are ambiguous in
1.1Schristospractice. For example, in English-speaking North America
1.1Schristos"<abbr>CST</abbr>" denotes 6 hours behind <abbr>UT</abbr>,
1.1Schristosbut in China it denotes 8 hours ahead of <abbr>UT</abbr>,
1.1Schristosand French-speaking North Americans prefer
1.1Schristos"<abbr title="Heure Normale du Centre">HNC</abbr>" to
1.1Schristos"<abbr>CST</abbr>". The <code><abbr>tz</abbr></code>
1.2Schristosdatabase contains English abbreviations for many timestamps;
1.1Schristosunfortunately some of these abbreviations were merely the database maintainers'
1.1Schristosinventions, and these have been removed when possible.</li>
1.1Schristos<li>Numeric time zone abbreviations typically count hours east of
1.1Schristos<abbr>UT</abbr>, e.g., +09 for Japan and
1.1Schristos&minus;10 for Hawaii. However, the <abbr>POSIX</abbr>
1.1Schristos<code><abbr>TZ</abbr></code> environment variable uses the opposite convention.
1.1SchristosFor example, one might use <code><abbr>TZ</abbr>="<abbr
1.1Schristostitle="Japan Standard Time">JST</abbr>-9"</code> and
1.1Schristos<code><abbr>TZ</abbr>="<abbr title="Hawaii Standard Time">HST</abbr>10"</code>
1.1Schristosfor Japan and Hawaii, respectively. If the
1.1Schristos<code><abbr>tz</abbr></code> database is available, it is usually better to use
1.1Schristossettings like <code><abbr>TZ</abbr>="Asia/Tokyo"</code> and
1.1Schristos<code><abbr>TZ</abbr>="Pacific/Honolulu"</code> instead, as this should avoid
1.2Schristosconfusion, handle old timestamps better, and insulate you better from
1.1Schristosany future changes to the rules. One should never set
1.1Schristos<abbr>POSIX</abbr> <code><abbr>TZ</abbr></code> to a value like
1.1Schristos<code>"GMT-9"</code>, though, since this would incorrectly imply that
1.1Schristoslocal time is nine hours ahead of <abbr>UT</abbr> and the time zone
1.1Schristosis called "<abbr>GMT</abbr>".</li>
1.1Schristos</ul>
1.1Schristos<h2 id="see-also">See also</h2>
1.1Schristos<ul>
1.1Schristos<li><a href="theory.html">Theory and pragmatics of the tz code and data</a></li>
1.1Schristos<li><a href="tz-art.html">Time and the Arts</a></li>
1.1Schristos</ul>
1.1Schristos<hr>
1.1Schristos<address>
1.1SchristosThis web page is in the public domain, so clarified as of
1.1Schristos2009-05-17 by Arthur David Olson.
1.1Schristos<br>
1.1SchristosPlease send corrections to this web page to the
1.1Schristos<a href="mailto:tz@iana.org">time zone mailing list</a>.
1.1Schristos</address>
1.1Schristos</body>
1.1Schristos</html>