Sources for Time Zone and Daylight Saving Time Data

@(#)tz-link.htm 7.37

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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, DJGPP, HP-UX, IRIX, Open UNIX/UnixWare, Solaris, and Tru64.

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 'ftp://elsie.nci.nih.gov/pub/tz*.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, or retrieve the archive of old messages (in gzip compressed format).

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 tz compilers

Other tz binary file readers

Other tz-based time zone conversion software

Other time zone databases

Maps

Time zone boundaries

Daylight saving time concepts and history

Precision timekeeping

Time notation

Related indexes