1.\" $NetBSD: tzfile.5,v 1.16 2011/09/04 10:10:26 christos Exp $ 2.\" 3.\" @(#)tzfile.5 7.11 4.\" This file is in the public domain, so clarified as of 5.\" 1996-06-05 by Arthur David Olson (arthur_david_olson@nih.gov). 6.Dd September 16, 2001 7.Dt TZFILE 5 8.Os 9.Sh NAME 10.Nm tzfile 11.Nd time zone information 12.Sh SYNOPSIS 13.In tzfile.h 14.Sh DESCRIPTION 15The time zone information files used by 16.Xr tzset 3 17begin with the magic characters 18.Dq TZif 19to identify them as time zone information files, 20followed by a character identifying the version of the file's format 21(as of 2005, either an ASCII NUL or a '2') 22followed by fifteen bytes containing zeroes reserved for future use, 23followed by six four-byte values of type 24.Fa long , 25written in a 26.Dq standard 27byte order (the high-order byte of the value is written first). 28These values are, in order: 29.Bl -tag -width XXXXXX -compact 30.It Va tzh_ttisgmtcnt 31The number of UTC/local indicators stored in the file. 32.It Va tzh_ttisstdcnt 33The number of standard/wall indicators stored in the file. 34.It Va tzh_leapcnt 35The number of leap seconds for which data is stored in the file. 36.It Va tzh_timecnt 37The number of 38.Dq transition times 39for which data is stored in the file. 40.It Va tzh_typecnt 41The number of 42.Dq local time types 43for which data is stored in the file (must not be zero). 44.It Va tzh_charcnt 45The number of characters of "time zone abbreviation strings" 46stored in the file. 47.El 48.Pp 49The above header is followed by 50.Va tzh_timecnt 51four-byte values of type 52.Fa long , 53sorted in ascending order. 54These values are written in 55.Dq standard 56byte order. 57Each is used as a transition time (as returned by 58.Xr time 3 ) 59at which the rules for computing local time change. 60Next come 61.Va tzh_timecnt 62one-byte values of type 63.Fa unsigned char ; 64each one tells which of the different types of 65.Dq local time 66types described in the file is associated with the same-indexed 67transition time. 68These values serve as indices into an array of 69.Fa ttinfo 70structures (with 71.Va tzh_typecnt 72entries) that appears next in the file; 73these structures are defined as follows: 74.Bd -literal 75struct ttinfo { 76 long tt_gmtoff; 77 int tt_isdst; 78 unsigned int tt_abbrind; 79}; 80.Ed 81Each structure is written as a four-byte value for 82.Va tt_gmtoff 83of type 84.Fa long , 85in a standard byte order, followed by a one-byte value for 86.Va tt_isdst 87and a one-byte value for 88.Va tt_abbrind . 89In each structure, 90.Va tt_gmtoff 91gives the number of seconds to be added to UTC, 92.Va tt_isdst 93tells whether 94.Va tm_isdst 95should be set by 96.Xr localtime 3 97and 98.Va tt_abbrind 99serves as an index into the array of time zone abbreviation characters 100that follow the 101.Va ttinfo 102structure(s) in the file. 103.Pp 104Then there are 105.Va tzh_leapcnt 106pairs of four-byte values, written in standard byte order; 107the first value of each pair gives the time 108(as returned by 109.Xr time 3 ) 110at which a leap second occurs; 111the second gives the 112.Em total 113number of leap seconds to be applied after the given time. 114The pairs of values are sorted in ascending order by time. 115.Pp 116Then there are 117.Va tzh_ttisstdcnt 118standard/wall indicators, each stored as a one-byte value; 119they tell whether the transition times associated with local time types 120were specified as standard time or wall clock time, 121and are used when a time zone file is used in handling POSIX-style 122time zone environment variables. 123.Pp 124Finally there are 125.Va tzh_ttisgmtcnt 126UTC/local indicators, each stored as a one-byte value; 127they tell whether the transition times associated with local time types 128were specified as UTC or local time, 129and are used when a time zone file is used in handling POSIX-style 130time zone environment variables. 131.Pp 132.Xr localtime 3 133uses the first standard-time 134.Fa ttinfo 135structure in the file 136(or simply the first 137.Fa ttinfo 138structure in the absence of a standard-time structure) 139if either 140.Va tzh_timecnt 141is zero or the time argument is less than the first transition time recorded 142in the file. 143.Pp 144For version-2-format time zone files, 145the above header and data is followed by a second header and data, 146identical in format except that 147eight bytes are used for each transition time or leap second time. 148After the second header and data comes a newline-enclosed, 149POSIX-TZ-environment-variable-style string for use in handling instants 150after the last transition time stored in the file 151(with nothing between the newlines if there is no POSIX representation for 152such instants). 153.Sh SEE ALSO 154.Xr ctime 3 , 155.Xr localtime 3 , 156.Xr time 3 157.\" @(#)tzfile.5 8.3 158.\" This file is in the public domain, so clarified as of 159.\" 1996-06-05 by Arthur David Olson. 160