tzset, tzname, timezone, daylight — initialize time conversion information
extern char *tzname; extern long timezone; extern int daylight;
variable. This function is automatically called by the other
time conversion functions that depend on the timezone. In a
System-V-like environment, it will also set the variables
timezone (seconds West of UTC)
daylight (to 0 if this
timezone does not have any daylight saving time rules, or to
nonzero if there is a time, past, present or future when
daylight saving time applies).
TZ variable does not
appear in the environment, the system timezone is used. The
system timezone is configured by copying, or linking, a file
in the tzfile(5) format to
/etc/localtime. A timezone
database of these files may be located in the system timezone
directory (see the
TZ variable does
appear in the environment, but its value is empty, or its
value cannot be interpreted using any of the formats
specified below, then Coordinated Universal Time (UTC) is
The value of
TZ can be one
of two formats. The first format is a string of characters
that directly represent the timezone to be used:
There are no spaces in the specification. The
std string specifies an abbreviation for the
timezone and must be three or more alphabetic characters.
When enclosed between the less-than (<) and greater-than
(>) signs, the characters set is expanded to include the
plus (+) sign, the minus (-) sign, and digits. The
offset string immediately
std and specifies the
time value to be added to the local time to get Coordinated
Universal Time (UTC). The
is positive if the local timezone is west of the Prime
Meridian and negative if it is east. The hour must be between
0 and 24, and the minutes and seconds 00 and 59:
dst string and
offset specify the name and
offset for the corresponding daylight saving timezone. If the
offset is omitted, it defaults to one hour ahead of standard
start field specifies
when daylight saving time goes into effect and the
end field specifies when the
change is made back to standard time. These fields may have
the following formats:
This specifies the Julian day with
n between 1 and 365. Leap days are not
counted. In this format, February 29 can't be
represented; February 28 is day 59, and March 1 is
always day 60.
This specifies the zero-based Julian day with
n between 0 and 365.
February 29 is counted in leap years.
This specifies day
d <= 6) of week
w (1 <=
w <= 5) of month
m (1 <=
m <= 12). Week 1 is the first week
in which day
d occurs and
week 5 is the last week in which day
d occurs. Day 0 is a Sunday.
time fields specify
when, in the local time currently in effect, the change to
the other time occurs. If omitted, the default is
Here is an example for New Zealand, where the standard time (NZST) is 12 hours ahead of UTC, and daylight saving time (NZDT), 13 hours ahead of UTC, runs from the first Sunday in October to the third Sunday in March, and the changeovers happen at the default time of 02:00:00:
The second format specifies that the timezone information should be read from a file:
If the file specification
filespec is omitted, or its value cannot be
interpreted, then Coordinated Universal Time (UTC) is used.
filespec is given, it
specifies another tzfile(5)-format file to
read the timezone information from. If
filespec does not begin with a '/', the file
specification is relative to the system timezone directory.
If the colon is omitted each of the above
TZ formats will be tried.
Here's an example, once more for New Zealand:
If this variable is set its value takes precedence over the system configured timezone.
If this variable is set its value takes precedence over the system configured timezone database directory path.
The system timezone file.
The system timezone database directory.
When a TZ string includes a dst timezone without
anything following it, then this file is used for the
start/end rules. It is in the tzfile(5) format. By
default, the zoneinfo Makefile hard links it to the
Above are the current standard file locations, but they are configurable when glibc is compiled.
For an explanation of the terms used in this section, see attributes(7).
||Thread safety||MT-Safe env locale|
4.3BSD had a function
dst) that returned the name of
the timezone corresponding to its first argument (minutes
West of UTC). If the second argument was 0, the standard name
was used, otherwise the daylight saving time version.
This page is part of release 4.07 of the Linux
man-pages project. A
description of the project, information about reporting bugs,
and the latest version of this page, can be found at
Copyright 1993 David Metcalfe (davidprism.demon.co.uk)
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Linux libc source code
Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
386BSD man pages
Modified Sun Jul 25 11:01:58 1993 by Rik Faith (faithcs.unc.edu)
Modified 2001-11-13, aeb
Modified 2004-12-01 mtk and Martin Schulze <joeyinfodrom.org>