Sources for Time Zone and Daylight Saving Time Data

@(#)tz-link.htm 7.42

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The tz database

The public-domain 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 UTC offsets and daylight-saving rules. This database (often called tz or zoneinfo) is used by several implementations, including the GNU C Library used in GNU/Linux, FreeBSD, NetBSD, OpenBSD, Cygwin, DJGPP, HP-UX, IRIX, Mac OS X, OpenVMS, Solaris, Tru64, and UnixWare.

Each location in the database represents a national region where all clocks keeping local time have agreed since 1970. Locations are identified by continent or ocean and then by the name of the location, which is typically the largest city within the region. For example, America/New_York represents most of the US eastern time zone; America/Indianapolis represents most of Indiana, which uses eastern time without daylight saving time (DST); America/Detroit represents most of Michigan, which uses eastern time but with different DST rules in 1975; and other entries represent smaller regions like Starke County, Kentucky, which switched from central to eastern time in 1991. To use the database, set the TZ environment variable to the location's full name, e.g., TZ="America/New_York".

In the tz database's FTP distribution, the code is in the file tzcodeC.tar.gz, where C is the code's version; similarly, the data are in tzdataD.tar.gz, where D is the data's version. The following shell commands download these files to a GNU/Linux or similar host; see the downloaded README file for what to do next.

wget '*.tar.gz'
gzip -dc tzcode*.tar.gz | tar -xf -
gzip -dc tzdata*.tar.gz | tar -xf -

The code lets you compile the tz source files into machine-readable binary files, one for each location. It also lets you read a tz binary file and interpret time stamps for that location.

The data are by no means authoritative. If you find errors, please send changes to the time zone mailing list. You can also subscribe to the mailing list, retrieve the archive of old messages (in gzip compressed format), or retrieve archived older versions of code and data.

The Web has several other sources for time zone and daylight saving time data. Here are some recent links that may be of interest.

Web pages using recent versions of the tz database

Other time zone database formats

Other tz compilers

Other tz binary file readers

Other tz-based time zone conversion software

Other time zone databases


Time zone boundaries

Civil time concepts and history

National histories of legal time

The Community Relations Division of the New South Wales (NSW) Attorney General's Department maintains a history of daylight saving in NSW.
The Federal Office of Metrology and Surveying publishes a table of daylight saving time in Austria (in German).
The Royal Observatory of Belgium maintains a table of time in Belgium (in Dutch).
The Time Service Department of the National Observatory records Brazil's daylight saving time decrees (in Portuguese).
The Institute for National Measurement Standards publishes current and some older information about Time Zones and Daylight Saving Time.
WebExhibits publishes a history of official time (in Spanish) originally written by the Chilean Hydrographic and Oceanographic Service.
The National Institute for Science and Technology maintains the Realisation of Legal Time in Germany.
The Interior Ministry periodically issues announcements (in Hebrew).
The Investigation and Analysis Service of the Mexican Library of Congress has published a history of Mexican local time (in Spanish).
See Singapore below.
Legal time in the Netherlands (in Dutch) covers the history of local time in the Netherlands from ancient times.
New Zealand
The Department of Internal Affairs maintains a brief history about daylight saving. The privately-maintained Time Changes in New Zealand has more details.
Why is Singapore in the "Wrong" Time Zone? details the history of legal time in Singapore and Malaysia.
United Kingdom
History of legal time in Britain discusses in detail the country with perhaps the best-documented history of clock adjustments. The National Physical Laboratory also maintains an archive of summer time dates.

Precision timekeeping

Time notation

Related indexes