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TZSET(3) | Linux Programmer's Manual | TZSET(3) |
NAME¶
tzset, tzname, timezone, daylight - initialize time conversion informationSYNOPSIS¶
#include <time.h>void tzset (void);extern char *tzname[2]; extern long timezone; extern int daylight;
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
DESCRIPTION¶
The tzset() function initializes the tzname variable from the TZ environment 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) and daylight (to 0 if this timezone does not have any daylight saving time rules, or to nonzero if there is a time during the year when daylight saving time applies). If the TZ variable does not appear in the environment, the tzname variable is initialized with the best approximation of local wall clock time, as specified by the tzfile(5)-format file localtime found in the system timezone directory (see below). (One also often sees /etc/localtime used here, a symlink to the right file in the system timezone directory.) If 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, Coordinated Universal Time (UTC) is used. The value of TZ can be one of three formats. The first format is used when there is no daylight saving time in the local timezone:std offset
std offset dst
[offset],start[/time],end[/time]
- Jn
- 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.
- n
- This specifies the zero-based Julian day with n between 0 and 365. February 29 is counted in leap years.
- Mm.w.d
- This specifies day d (0 <= 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.
TZ="NZST-12:00:00NZDT-13:00:00,M10.1.0,M3.3.0"The third format specifies that the timezone information should be read from a file:
:[filespec]
TZ=":Pacific/Auckland"
FILES¶
The system timezone directory used depends on the (g)libc version. Libc4 and libc5 use /usr/lib/zoneinfo, and, since libc-5.4.6, when this doesn't work, will try /usr/share/zoneinfo. Glibc2 will use the environment variable TZDIR, when that exists. Its default depends on how it was installed, but normally is /usr/share/zoneinfo. This timezone directory contains the fileslocaltime local timezone file posixrules rules for POSIX-style TZ'sOften /etc/localtime is a symlink to the file localtime or to the correct timezone file in the system timezone directory.
CONFORMING TO¶
SVr4, POSIX.1-2001, 4.3BSD.NOTES¶
Note that the variable daylight does not indicate that daylight saving time applies right now. It used to give the number of some algorithm (see the variable tz_dsttime in gettimeofday(2)). It has been obsolete for many years but is required by SUSv2. 4.3BSD had a function char *timezone(zone, 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.SEE ALSO¶
date(1), gettimeofday(2), time(2), ctime(3), getenv(3), tzfile(5)COLOPHON¶
This page is part of release 3.44 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.2012-03-25 |