tz(5) [minix man page]

TZ(5)								File Formats Manual							     TZ(5)

NAME

       TZ - Time zone environment variable

SYNOPSIS

       TZ=zone[-]offset[dst[offset][,start[/time],end[/time]]]

DESCRIPTION

       The  TZ environment variable tells functions such as the ctime(3) family and programs like date what the time zone and daylight saving rule
       is.  The value of TZ has the POSIX standardized form shown in the synopsis.  This form specifies the zone names, offsets from GMT, and day-
       light savings changeover times for at least the current year.

       zone   A three or more letter name for the time zone in normal (winter) time.

       [-]offset
	      A  signed  time  telling the offset of the time zone westwards from Greenwich.  The time has the form hh[:mm[:ss]] with a one of two
	      digit hour, and optional two digit minutes and seconds.

       dst    The name of the time zone when daylight savings is in effect.  It may be followed by an offset telling how big the clock	correction
	      is other than the default of 1 hour.

       start/time,end/time
	      Specifies  the  start  and end of the daylight savings period.  The start and end fields indicate on what day the changeover occurs.
	      They must be in one of the following formats:

	      Jn   The Julian day n (1 <= n <= 365) ignoring leap days, i.e. there is no February 29.

	      n    The zero-based Julian day (0 <= n <= 365).  Leap days are not ignored.

	      Mm.n.d
		   This indicates month m, the n-th occurrence of day d (1 <= m <= 12, 1 <= n <= 5, 0 <= d <= 6, 0=Sunday).  The  5-th	occurrence
		   means the last occurrence of that day in a month.  So M4.1.0 is the first Sunday in April, M9.5.0 is the last Sunday in Septem-
		   ber.

	      The time field indicates the time the changeover occurs on the given day.

EXAMPLES

       Greenwich Mean Time:

	      TZ=GMT0

       Middle European Time, 1 hour east from Greenwich, daylight savings starts on the last Sunday in March at 2 AM and ends on the  last  Sunday
       in October at 3 AM:

	      TZ='MET-1MET DST,M3.5.0/2,M10.5.0/3'

       British time, daylight savings starts and ends at the same moment as MET, but in an earlier time zone:

	      TZ=GMT0BST,M3.5.0/1,M10.5.0/2

       The eastern european time zones also have the changeovers at the same absolute time as British time and MET.

       U.S.  Eastern Standard Time, 5 hours west from Greenwich, daylight savings starts on the first Sunday in April at 2 AM and ends on the last
       Sunday in October at 2 AM:

	      TZ=EST5EDT,M4.1.0/2,M10.5.0/2

       It shouldn't surprise you that daylight savings in New Zealand is observed in the months opposite from the previous examples.  It starts on
       the first Sunday in October at 2 AM and ends on the third Sunday in March at 3 AM:

	      TZ=NZST-12NZDT,M10.1.0/2,M3.3.0/3

SEE ALSO

       readclock(8), date(1).

BUGS

       You  may  have  noticed that many fields are optional.  Do no omit them, because the defaults are bogus.  If you need daylight savings then
       fully specify the changeovers.

       West is negative, east is positive, ask any sailor.

AUTHOR

       Kees J. Bot (kjb@cs.vu.nl)

																	     TZ(5)

TZSET(3)						     Linux Programmer's Manual							  TZSET(3)

NAME

       tzset, tzname, timezone, daylight - initialize time conversion information

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 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 speci-
       fied 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 Coordinated 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]

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

       The 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:

       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 repre-
	      sented; 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.

       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 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 timezone file
       posixrules     rules for POSIX-style TZ's

       Often /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 algo-
       rithm (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								  TZSET(3)