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diff --git a/man5/tzfile.5 b/man5/tzfile.5 deleted file mode 100644 index 4aa3f6c..0000000 --- a/man5/tzfile.5 +++ /dev/null @@ -1,508 +0,0 @@ -.\" This file is in the public domain, so clarified as of -.\" 1996-06-05 by Arthur David Olson. -.TH tzfile 5 "" "Time Zone Database" -.SH NAME -tzfile \- timezone information -.SH DESCRIPTION -.ie '\(lq'' .ds lq \&"\" -.el .ds lq \(lq\" -.ie '\(rq'' .ds rq \&"\" -.el .ds rq \(rq\" -.de q -\\$3\*(lq\\$1\*(rq\\$2 -.. -.ie \n(.g .ds - \f(CR-\fP -.el .ds - \- -The timezone information files used by -.BR tzset (3) -are typically found under a directory with a name like -.IR /usr/share/zoneinfo . -These files use the format described in Internet RFC 8536. -Each file is a sequence of 8-bit bytes. -In a file, a binary integer is represented by a sequence of one or -more bytes in network order (bigendian, or high-order byte first), -with all bits significant, -a signed binary integer is represented using two's complement, -and a boolean is represented by a one-byte binary integer that is -either 0 (false) or 1 (true). -The format begins with a 44-byte header containing the following fields: -.RS 2 -.IP \(bu 3 -The magic four-byte ASCII sequence -.q "TZif" -identifies the file as a timezone information file. -.IP \(bu -A byte identifying the version of the file's format -(as of 2021, either an ASCII NUL, -.q "2", -.q "3", -or -.q "4" ). -.IP \(bu -Fifteen bytes containing zeros reserved for future use. -.IP \(bu -Six four-byte integer values, in the following order: -.RS -.TP 2 -.B tzh_ttisutcnt -The number of UT/local indicators stored in the file. -(UT is Universal Time.) -.TP -.B tzh_ttisstdcnt -The number of standard/wall indicators stored in the file. -.TP -.B tzh_leapcnt -The number of leap seconds for which data entries are stored in the file. -.TP -.B tzh_timecnt -The number of transition times for which data entries are stored -in the file. -.TP -.B tzh_typecnt -The number of local time types for which data entries are stored -in the file (must not be zero). -.TP -.B tzh_charcnt -The number of bytes of time zone abbreviation strings -stored in the file. -.RE -.RE -.PP -The above header is followed by the following fields, whose lengths -depend on the contents of the header: -.RS 2 -.IP \(bu 3 -.B tzh_timecnt -four-byte signed integer values sorted in ascending order. -These values are written in network byte order. -Each is used as a transition time (as returned by -.BR time (2)) -at which the rules for computing local time change. -.IP \(bu -.B tzh_timecnt -one-byte unsigned integer values; -each one but the last tells which of the different types of local time types -described in the file is associated with the time period -starting with the same-indexed transition time -and continuing up to but not including the next transition time. -(The last time type is present only for consistency checking with the -POSIX.1-2017-style TZ string described below.) -These values serve as indices into the next field. -.IP \(bu -.B tzh_typecnt -.B ttinfo -entries, each defined as follows: -.in +2 -.sp -.nf -.ta \w'\0\0\0\0'u +\w'unsigned char\0'u -struct ttinfo { - int32_t tt_utoff; - unsigned char tt_isdst; - unsigned char tt_desigidx; -}; -.in -.fi -.sp -Each structure is written as a four-byte signed integer value for -.BR tt_utoff , -in network byte order, followed by a one-byte boolean for -.B tt_isdst -and a one-byte value for -.BR tt_desigidx . -In each structure, -.B tt_utoff -gives the number of seconds to be added to UT, -.B tt_isdst -tells whether -.B tm_isdst -should be set by -.BR localtime (3) -and -.B tt_desigidx -serves as an index into the array of time zone abbreviation bytes -that follow the -.B ttinfo -entries in the file; if the designated string is "\*-00", the -.B ttinfo -entry is a placeholder indicating that local time is unspecified. -The -.B tt_utoff -value is never equal to \-2**31, to let 32-bit clients negate it without -overflow. -Also, in realistic applications -.B tt_utoff -is in the range [\-89999, 93599] (i.e., more than \-25 hours and less -than 26 hours); this allows easy support by implementations that -already support the POSIX-required range [\-24:59:59, 25:59:59]. -.IP \(bu -.B tzh_charcnt -bytes that represent time zone designations, -which are null-terminated byte strings, each indexed by the -.B tt_desigidx -values mentioned above. -The byte strings can overlap if one is a suffix of the other. -The encoding of these strings is not specified. -.IP \(bu -.B tzh_leapcnt -pairs of four-byte values, written in network byte order; -the first value of each pair gives the nonnegative time -(as returned by -.BR time (2)) -at which a leap second occurs or at which the leap second table expires; -the second is a signed integer specifying the correction, which is the -.I total -number of leap seconds to be applied during the time period -starting at the given time. -The pairs of values are sorted in strictly ascending order by time. -Each pair denotes one leap second, either positive or negative, -except that if the last pair has the same correction as the previous one, -the last pair denotes the leap second table's expiration time. -Each leap second is at the end of a UTC calendar month. -The first leap second has a nonnegative occurrence time, -and is a positive leap second if and only if its correction is positive; -the correction for each leap second after the first differs -from the previous leap second by either 1 for a positive leap second, -or \-1 for a negative leap second. -If the leap second table is empty, the leap-second correction is zero -for all timestamps; -otherwise, for timestamps before the first occurrence time, -the leap-second correction is zero if the first pair's correction is 1 or \-1, -and is unspecified otherwise (which can happen only in files -truncated at the start). -.IP \(bu -.B tzh_ttisstdcnt -standard/wall indicators, each stored as a one-byte boolean; -they tell whether the transition times associated with local time types -were specified as standard time or local (wall clock) time. -.IP \(bu -.B tzh_ttisutcnt -UT/local indicators, each stored as a one-byte boolean; -they tell whether the transition times associated with local time types -were specified as UT or local time. -If a UT/local indicator is set, the corresponding standard/wall indicator -must also be set. -.RE -.PP -The standard/wall and UT/local indicators were designed for -transforming a TZif file's transition times into transitions appropriate -for another time zone specified via -a POSIX.1-2017-style TZ string that lacks rules. -For example, when TZ="EET\*-2EEST" and there is no TZif file "EET\*-2EEST", -the idea was to adapt the transition times from a TZif file with the -well-known name "posixrules" that is present only for this purpose and -is a copy of the file "Europe/Brussels", a file with a different UT offset. -POSIX does not specify this obsolete transformational behavior, -the default rules are installation-dependent, and no implementation -is known to support this feature for timestamps past 2037, -so users desiring (say) Greek time should instead specify -TZ="Europe/Athens" for better historical coverage, falling back on -TZ="EET\*-2EEST,M3.5.0/3,M10.5.0/4" if POSIX conformance is required -and older timestamps need not be handled accurately. -.PP -The -.BR localtime (3) -function -normally uses the first -.B ttinfo -structure in the file -if either -.B tzh_timecnt -is zero or the time argument is less than the first transition time recorded -in the file. -.SS Version 2 format -For version-2-format timezone files, -the above header and data are followed by a second header and data, -identical in format except that -eight bytes are used for each transition time or leap second time. -(Leap second counts remain four bytes.) -After the second header and data comes a newline-enclosed string -in the style of the contents of a POSIX.1-2017 TZ environment variable, -for use in handling instants -after the last transition time stored in the file -or for all instants if the file has no transitions. -The TZ string is empty (i.e., nothing between the newlines) -if there is no POSIX.1-2017-style representation for such instants. -If nonempty, the TZ string must agree with the local time -type after the last transition time if present in the eight-byte data; -for example, given the string -.q "WET0WEST,M3.5.0/1,M10.5.0" -then if a last transition time is in July, the transition's local time -type must specify a daylight-saving time abbreviated -.q "WEST" -that is one hour east of UT. -Also, if there is at least one transition, time type 0 is associated -with the time period from the indefinite past up to but not including -the earliest transition time. -.SS Version 3 format -For version-3-format timezone files, the TZ string may -use two minor extensions to the POSIX.1-2017 TZ format, as described in -.BR newtzset (3). -First, the hours part of its transition times may be signed and range from -\-167 through 167 instead of the POSIX-required unsigned values -from 0 through 24. -Second, DST is in effect all year if it starts -January 1 at 00:00 and ends December 31 at 24:00 plus the difference -between daylight saving and standard time. -.SS Version 4 format -For version-4-format TZif files, -the first leap second record can have a correction that is neither -+1 nor \-1, to represent truncation of the TZif file at the start. -Also, if two or more leap second transitions are present and the last -entry's correction equals the previous one, the last entry -denotes the expiration of the leap second table instead of a leap second; -timestamps after this expiration are unreliable in that future -releases will likely add leap second entries after the expiration, and -the added leap seconds will change how post-expiration timestamps are treated. -.SS Interoperability considerations -Future changes to the format may append more data. -.PP -Version 1 files are considered a legacy format and -should not be generated, as they do not support transition -times after the year 2038. -Readers that understand only Version 1 must ignore -any data that extends beyond the calculated end of the version -1 data block. -.PP -Other than version 1, writers should generate -the lowest version number needed by a file's data. -For example, a writer should generate a version 4 file -only if its leap second table either expires or is truncated at the start. -Likewise, a writer not generating a version 4 file -should generate a version 3 file only if -TZ string extensions are necessary to accurately -model transition times. -.PP -The sequence of time changes defined by the version 1 -header and data block should be a contiguous sub-sequence -of the time changes defined by the version 2+ header and data -block, and by the footer. -This guideline helps obsolescent version 1 readers -agree with current readers about timestamps within the -contiguous sub-sequence. It also lets writers not -supporting obsolescent readers use a -.B tzh_timecnt -of zero -in the version 1 data block to save space. -.PP -When a TZif file contains a leap second table expiration -time, TZif readers should either refuse to process -post-expiration timestamps, or process them as if the expiration -time did not exist (possibly with an error indication). -.PP -Time zone designations should consist of at least three (3) -and no more than six (6) ASCII characters from the set of -alphanumerics, -.q "\*-", -and -.q "+". -This is for compatibility with POSIX requirements for -time zone abbreviations. -.PP -When reading a version 2 or higher file, readers -should ignore the version 1 header and data block except for -the purpose of skipping over them. -.PP -Readers should calculate the total lengths of the -headers and data blocks and check that they all fit within -the actual file size, as part of a validity check for the file. -.PP -When a positive leap second occurs, readers should append an extra -second to the local minute containing the second just before the leap -second. If this occurs when the UTC offset is not a multiple of 60 -seconds, the leap second occurs earlier than the last second of the -local minute and the minute's remaining local seconds are numbered -through 60 instead of the usual 59; the UTC offset is unaffected. -.SS Common interoperability issues -This section documents common problems in reading or writing TZif files. -Most of these are problems in generating TZif files for use by -older readers. -The goals of this section are: -.RS 2 -.IP \(bu 3 -to help TZif writers output files that avoid common -pitfalls in older or buggy TZif readers, -.IP \(bu -to help TZif readers avoid common pitfalls when reading -files generated by future TZif writers, and -.IP \(bu -to help any future specification authors see what sort of -problems arise when the TZif format is changed. -.RE -.PP -When new versions of the TZif format have been defined, a -design goal has been that a reader can successfully use a TZif -file even if the file is of a later TZif version than what the -reader was designed for. -When complete compatibility was not achieved, an attempt was -made to limit glitches to rarely used timestamps and allow -simple partial workarounds in writers designed to generate -new-version data useful even for older-version readers. -This section attempts to document these compatibility issues and -workarounds, as well as to document other common bugs in -readers. -.PP -Interoperability problems with TZif include the following: -.RS 2 -.IP \(bu 3 -Some readers examine only version 1 data. -As a partial workaround, a writer can output as much version 1 -data as possible. -However, a reader should ignore version 1 data, and should use -version 2+ data even if the reader's native timestamps have only -32 bits. -.IP \(bu -Some readers designed for version 2 might mishandle -timestamps after a version 3 or higher file's last transition, because -they cannot parse extensions to POSIX.1-2017 in the TZ-like string. -As a partial workaround, a writer can output more transitions -than necessary, so that only far-future timestamps are -mishandled by version 2 readers. -.IP \(bu -Some readers designed for version 2 do not support -permanent daylight saving time with transitions after 24:00 -\(en e.g., a TZ string -.q "EST5EDT,0/0,J365/25" -denoting permanent Eastern Daylight Time -(\-04). -As a workaround, a writer can substitute standard time -for two time zones east, e.g., -.q "XXX3EDT4,0/0,J365/23" -for a time zone with a never-used standard time (XXX, \-03) -and negative daylight saving time (EDT, \-04) all year. -Alternatively, -as a partial workaround a writer can substitute standard time -for the next time zone east \(en e.g., -.q "AST4" -for permanent -Atlantic Standard Time (\-04). -.IP \(bu -Some readers designed for version 2 or 3, and that require strict -conformance to RFC 8536, reject version 4 files whose leap second -tables are truncated at the start or that end in expiration times. -.IP \(bu -Some readers ignore the footer, and instead predict future -timestamps from the time type of the last transition. -As a partial workaround, a writer can output more transitions -than necessary. -.IP \(bu -Some readers do not use time type 0 for timestamps before -the first transition, in that they infer a time type using a -heuristic that does not always select time type 0. -As a partial workaround, a writer can output a dummy (no-op) -first transition at an early time. -.IP \(bu -Some readers mishandle timestamps before the first -transition that has a timestamp not less than \-2**31. -Readers that support only 32-bit timestamps are likely to be -more prone to this problem, for example, when they process -64-bit transitions only some of which are representable in 32 -bits. -As a partial workaround, a writer can output a dummy -transition at timestamp \-2**31. -.IP \(bu -Some readers mishandle a transition if its timestamp has -the minimum possible signed 64-bit value. -Timestamps less than \-2**59 are not recommended. -.IP \(bu -Some readers mishandle TZ strings that -contain -.q "<" -or -.q ">". -As a partial workaround, a writer can avoid using -.q "<" -or -.q ">" -for time zone abbreviations containing only alphabetic -characters. -.IP \(bu -Many readers mishandle time zone abbreviations that contain -non-ASCII characters. -These characters are not recommended. -.IP \(bu -Some readers may mishandle time zone abbreviations that -contain fewer than 3 or more than 6 characters, or that -contain ASCII characters other than alphanumerics, -.q "\*-", -and -.q "+". -These abbreviations are not recommended. -.IP \(bu -Some readers mishandle TZif files that specify -daylight-saving time UT offsets that are less than the UT -offsets for the corresponding standard time. -These readers do not support locations like Ireland, which -uses the equivalent of the TZ string -.q "IST\*-1GMT0,M10.5.0,M3.5.0/1", -observing standard time -(IST, +01) in summer and daylight saving time (GMT, +00) in winter. -As a partial workaround, a writer can output data for the -equivalent of the TZ string -.q "GMT0IST,M3.5.0/1,M10.5.0", -thus swapping standard and daylight saving time. -Although this workaround misidentifies which part of the year -uses daylight saving time, it records UT offsets and time zone -abbreviations correctly. -.IP \(bu -Some readers generate ambiguous timestamps for positive leap seconds -that occur when the UTC offset is not a multiple of 60 seconds. -For example, in a timezone with UTC offset +01:23:45 and with -a positive leap second 78796801 (1972-06-30 23:59:60 UTC), some readers will -map both 78796800 and 78796801 to 01:23:45 local time the next day -instead of mapping the latter to 01:23:46, and they will map 78796815 to -01:23:59 instead of to 01:23:60. -This has not yet been a practical problem, since no civil authority -has observed such UTC offsets since leap seconds were -introduced in 1972. -.RE -.PP -Some interoperability problems are reader bugs that -are listed here mostly as warnings to developers of readers. -.RS 2 -.IP \(bu 3 -Some readers do not support negative timestamps. -Developers of distributed applications should keep this -in mind if they need to deal with pre-1970 data. -.IP \(bu -Some readers mishandle timestamps before the first -transition that has a nonnegative timestamp. -Readers that do not support negative timestamps are likely to -be more prone to this problem. -.IP \(bu -Some readers mishandle time zone abbreviations like -.q "\*-08" -that contain -.q "+", -.q "\*-", -or digits. -.IP \(bu -Some readers mishandle UT offsets that are out of the -traditional range of \-12 through +12 hours, and so do not -support locations like Kiritimati that are outside this -range. -.IP \(bu -Some readers mishandle UT offsets in the range [\-3599, \-1] -seconds from UT, because they integer-divide the offset by -3600 to get 0 and then display the hour part as -.q "+00". -.IP \(bu -Some readers mishandle UT offsets that are not a multiple -of one hour, or of 15 minutes, or of 1 minute. -.RE -.SH SEE ALSO -.BR time (2), -.BR localtime (3), -.BR tzset (3), -.BR tzselect (8), -.BR zdump (8), -.BR zic (8). -.PP -Olson A, Eggert P, Murchison K. The Time Zone Information Format (TZif). -2019 Feb. -.UR https://\:datatracker.ietf.org/\:doc/\:html/\:rfc8536 -Internet RFC 8536 -.UE -.UR https://\:doi.org/\:10.17487/\:RFC8536 -doi:10.17487/RFC8536 -.UE . |