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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
       entries) 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_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 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
       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 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.
       After  the  second  header and data comes a newline-enclosed, POSIX-TZ-
       environment-variable-style string for use in  handling  instants  after
       the  last  transition time stored in the file (with nothing between the
       newlines 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)