tzname

       tion

SYNOPSIS
       #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)):

       tzset(): _POSIX_C_SOURCE >= 1 || _XOPEN_SOURCE || _POSIX_SOURCE
       tzname: _POSIX_C_SOURCE >= 1 || _XOPEN_SOURCE || _POSIX_SOURCE
       timezone: _SVID_SOURCE || _XOPEN_SOURCE
       daylight: _SVID_SOURCE || _XOPEN_SOURCE

DESCRIPTION
       The tzset() function initializes the tzname variable from the TZ  envi-
       ronment  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 vari-
       able  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 spec-
       ified 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

       The std string specifies the name of the timezone and must be three  or
       more  alphabetic characters.  The offset string immediately follows std
       and specifies the time value to be added to the local time to get Coor-
       dinated  Universal  Time  (UTC).   The  offset 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 0 and 59.

       The second format is used when there is daylight saving time:

              std offset dst [offset],start[/time],end[/time]


       n      This specifies the Julian day with n between 1 and 365.   Febru-
              ary 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.

       The time fields specify when, in the local time  currently  in  effect,
       the  change  to  the  other  time  occurs.   If omitted, the default is
       02:00:00.

       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:

           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]

       If the file specification filespec is omitted, the timezone information
       is read from the file localtime in the system timezone directory, which
       nowadays usually is /usr/share/zoneinfo.  This  file  is  in  tzfile(5)
       format.   If  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.

       Here's an example, once more for New Zealand:

           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  envi-
       ronment  variable  TZDIR, when that exists.  Its default depends on how
       it was installed, but normally is /usr/share/zoneinfo.

       This timezone directory contains the files
       localtime      local timezone file
       posixrules     rules for POSIX-style TZ's

       Often /etc/localtime is a symlink to the file localtime or to the  cor-
       rect timezone file in the system timezone directory.

CONFORMING TO
       SVr4, POSIX.1-2001, 4.3BSD.

       date(1), gettimeofday(2), time(2), ctime(3), getenv(3), tzfile(5)

COLOPHON
       This  page  is  part of release 3.35 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at http://man7.org/linux/man-pages/.



                                  2010-02-25                          TZSET(3)
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