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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.
tz
databasetz
's.tz
compilerstz
source into VTIMEZONE text as specified by
the iCalendar
specification published by the IETF
Calendaring and Scheduling Working Group. Vzic is freely
available under the GNU
General Public License (GPL).tz
data include one sketched out by Tim Berners-Lee and
another
used by the Sun
ONE Calendar Server.tz
binary file readerstz
binary file reader.
This library is freely available under the
GNU Lesser General Public License (LGPL),
and is widely used in GNU/Linux systems.tz
binary file reader written in Java.
It is freely available under the GNU LGPL.tz
-based time zone conversion softwareusno*
files in the tz
distribution.tz
database contains English abbreviations for all time
stamps but in many cases these are merely inventions of the database
maintainers.