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TZFILE(5)		   Linux Programmers Manual		    TZFILE(5)

       tzfile - time zone information


       This  page  describes the structure of timezone files as commonly found
       in /usr/lib/zoneinfo or /usr/share/zoneinfo.

       The time zone information files used by tzset(3) begin with  the  magic
       characters "TZif" to identify then as time zone information files, fol
       lowed by sixteen bytes 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:

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

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

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

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

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

	      The number of characters of  "time  zone	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 that appears 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_isdst  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 index into the array of time zone abbreviation  characters
       that follow the ttinfo structure(s) in the file.

       Then  there  are  tzh_leapcnt  pairs  of  four-byte  values, written in
       standard byte order; the first value of each pair gives	the  time  (as
       returned  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 time zone file is  used  in  handling	POSIX-
       style time zone 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 time zone file is used in handling POSIX-style time  zone  envi
       ronment variables.

       Localtime 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.

       This manual page documents  in the glibc source archive,  see

       It  seems  that	timezone  uses tzfile internally, but glibc refuses to
       expose it to userspace.	This is most likely because  the  standardised
       functions  are  more  useful  and  portable, and actually documented by
       glibc.  It may only be in glibc just  to  support  the  non-glibc-main
       tained timezone data (which is maintained by some other entity).

       time(3), gettimeofday(3), tzset(3), ctime(3)

       This  page  is  part of release 3.05 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/.

				  1996-06-05			     TZFILE(5)

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