NAME

       tzset - initialize time conversion information

SYNOPSIS

       #include <time.h>

       void tzset (void);

       extern char *tzname[2]

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 time zone.

       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 NULL 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 time zone:

              std offset

       The  std string specifies the name of the time zone 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
       Coordinated  Universal  Time  (UTC).   The offset is positive if the local time zone 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]

       There  are no spaces in the specification.  The initial std and offset specify the standard time zone, as
       described above.  The dst string and offset specify the name and offset for  the  corresponding  daylight
       savings time zone.  If the offset is omitted, it defaults  to one hour ahead of standard time.

       The  start  field  specifies when daylight savings 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:

       Jn     This specifies the Julian day with n between 1 and 365.  February 29 is never counted even in leap
              years.

       n      This specifies the Julian day with n between 1 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.

       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.

       The third format specifies that the time zone information should be read from a file:

              :[filespec]

       If the file specification filespec is omitted, the time zone 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 time zone
       information from.  If filespec does not begin with a `/', the  file  specification  is  relative  to  the
       system timezone directory.

FILES

       The   system   time   zone  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 files
       localtime      local time zone file
       posixrules     rules for POSIX-style TZ's

       Often /etc/localtime is a symlink to the file localtime or to the correct time zone file  in  the  system
       time zone directory.

CONFORMING TO

       SVID 3, POSIX, BSD 4.3

SEE ALSO

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

BSD                                               July 2, 1993                                          TZSET(3)