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TZFILE(5)		   Linux Programmer's Manual		     TZFILE(5)

NAME
       tzfile -	timezone information

DESCRIPTION
       This  page  describes  the  structure  of  the  timezone	 files used by
       tzset(3).  These	files are typically found under	one of the directories
       /usr/lib/zoneinfo or /usr/share/zoneinfo.

       Timezone	 information  files  begin with	the magic characters "TZif" to
       identify	them as	timezone information files, followed  by  a  character
       identifying  the	 version  of  the file's format	(as of 2005, either an
       ASCII NUL ('\0')	or a '2') followed by fifteen bytes  containing	 zeros
       reserved	for future use,	followed by six	four-byte values of type long,
       written in a "standard" byte order (the high-order byte of the value is
       written first).	These values are, in order:

       tzh_ttisgmtcnt
	      The number of UTC/local indicators stored	in the file.

       tzh_ttisstdcnt
	      The number of standard/wall indicators stored in the file.

       tzh_leapcnt
	      The number of leap seconds for which data	is stored in the file.

       tzh_timecnt
	      The number of "transition	times" for which data is stored	in the
	      file.

       tzh_typecnt
	      The number of "local time	types" for which data is stored	in the
	      file (must not be	zero).

       tzh_charcnt
	      The  number  of  characters  of  "timezone abbreviation strings"
	      stored in	the file.

       The above header	is followed by tzh_timecnt four-byte  values  of  type
       long,  sorted  in  ascending order.  These values are written in	"stan-
       dard" byte order.  Each is used as a transition time  (as  returned  by
       time(2))	at which the rules for computing local time change.  Next come
       tzh_timecnt one-byte values of type unsigned char; each one tells which
       of  the	different types	of "local time"	types described	in the file is
       associated with the same-indexed	transition time.  These	 values	 serve
       as  indices  into  an  array of ttinfo structures (with tzh_typecnt en-
       tries) that appear next in the file; these structures  are  defined  as
       follows:

	   struct ttinfo {
	       long	    tt_gmtoff;
	       int	    tt_isdst;
	       unsigned	int tt_abbrind;
	   };

       Each  structure	is  written as a four-byte value for tt_gmtoff of type
       long, in	a standard byte	order, followed	by a one-byte value for	tt_is-
       dst  and	a one-byte value for tt_abbrind.  In each structure, tt_gmtoff
       gives the number	of seconds to be added to UTC, tt_isdst	tells  whether
       tm_isdst	should be set by localtime(3), and tt_abbrind serves as	an in-
       dex into	the array of timezone abbreviation characters that follow  the
       ttinfo structure(s) in the file.

       Then  there are tzh_leapcnt pairs of four-byte values, written in stan-
       dard byte order;	the first value	of each	pair gives the	time  (as  re-
       turned  by time(2)) at which a leap second occurs; the second gives the
       total number of leap seconds to be applied after	the given  time.   The
       pairs of	values are sorted in ascending order by	time.

       Then  there are tzh_ttisstdcnt standard/wall indicators,	each stored as
       a one-byte value; they tell whether  the	 transition  times  associated
       with  local  time  types	 were specified	as standard time or wall clock
       time, and are used when a timezone file is used in handling POSIX-style
       timezone	environment variables.

       Finally,	 there are tzh_ttisgmtcnt UTC/local indicators,	each stored as
       a one-byte value; they tell whether  the	 transition  times  associated
       with local time types were specified as UTC or local time, and are used
       when a timezone file is used in handling	POSIX-style timezone  environ-
       ment variables.

       localtime(3)  uses the first standard-time ttinfo structure in the file
       (or simply the first ttinfo structure in	the absence of a standard-time
       structure)  if  either tzh_timecnt is zero or the time argument is less
       than the	first transition time recorded in the file.

       For version-2-format timezone files, the	above header and data is  fol-
       lowed  by  a  second  header  and data, identical in format except that
       eight bytes are used for	each transition	time or	leap-second time.  Af-
       ter the second header and data comes a newline-enclosed,	POSIX-TZ-envi-
       ronment-variable-style string for use in	handling  instants  after  the
       last  transition	time stored in the file	(with nothing between the new-
       lines if	there is no POSIX representation for such instants).

SEE ALSO
       ctime(3), tzset(3), tzselect(8),

       timezone/tzfile.h in the	glibc source tree

COLOPHON
       This page is part of release 3.53 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/.

				  2012-05-04			     TZFILE(5)

NAME | DESCRIPTION | SEE ALSO | COLOPHON

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