@database tzc.guide @author Carsten Larsen @(c) Carsten Larsen @$VER: tz.guide 5.00 (15.10.2016) @node Main "Amiga time zone database" @title "Amiga time zone database" "What time is it?" -- Richard Deacon as The King "Any time you want it to be." -- Frank Baxter as The Scientist (from the Bell System film "About Time") The Time Zone Database (often called tz or zoneinfo) contains code and data that represent the history of local time for many representative locations around the globe. It is updated periodically to reflect changes made by political bodies to time zone boundaries, UTC offsets, and daylight-saving rules. @{b}USER MANUALS@{ub} @{"Install " link "Install"} Install Amiga time zone database @{"TimeZone " link "TimeZone"} Select a time zone @{"TimeZoneInfo " link "TimeZoneInfo"} Show active time zone @{"SetClockGMT " link "SetClockGMT"} Set battery backed-up hardware clock in GMT @{"DSTCheck " link "DSTCheck"} Warn when daylight saving time changes @{"ZDump " link "ZDump"} Time zone dumper @{b}DEVELOPER MANUALS@{ub} @{"Library " link "library"} Time zone library @{"Zic " link "zic"} Time zone compiler @{"tzfile " link "tzfile"} Time zone information @{b}PROJECT MANUALS@{ub} @{"Contributing " link "CONTRIBUTING"} Contributing to the tz code and data @{"License " link "LICENSE"} Authors and terms @endnode @node Install "Install Amiga time zone database" @title "Install Amiga time zone database" @{b}INSTALL@{ub} Minimum * Copy timezone.library to Libs: * Assign ZONEINFO: to your zoneinfo directory * Copy zoneinfo from tzdata.lha to ZONEINFO: Optionally * Copy SetClockGMT to your systems C: * Copy TimeZone to your systems SYS:Prefs * Assign ZONEINFO: to LOCALE:Zoneinfo in S:Startup-Sequence * Add SetClockGMT NIL: LOAD to end of S:Startup-Sequence @{b}SETUP@{ub} Select a time zone in TimeZone GUI: TimeZone Save GMT time to RTC (hardware) clock: SetClockGMT SAVE Load GMT time to locale timezone: Add SetClockGMT LOAD to end of S:Startup-Sequence Validate time zone preferences in shell: TimeZoneInfo Show time in other time zones: Execute script/Show @endnode @node LICENSE "License and credits" @title "License and credits" @{b}LICENSE AND CREDITS@{ub} Unless otherwise specified, all files in the tz code and data are in the public domain, so clarified as of 2009-05-17 by Arthur David Olson. The few exceptions are code derived from BSD, which uses the BSD license. Thanks to these Time Zone Caballeros who've made major contributions to the time conversion package: Keith Bostic; Bob Devine; Paul Eggert; Robert Elz; Guy Harris; Mark Horton; John Mackin; and Bradley White. Thanks also to Michael Bloom, Art Neilson, Stephen Prince, John Sovereign, and Frank Wales for testing work, and to Gwillim Law for checking local mean time data. Thanks in particular to Arthur David Olson, the project's founder and first maintainer, to whom the time zone community owes the greatest debt of all. None of them are responsible for remaining errors. @endnode @node CONTRIBUTING "Contributing to the tz code and data" @title "Contributing to the tz code and data" @{bg filltext}@{b}Contributing Contributing@{ub}@{bg background} @{b}Contributing to the tz code and data (Non-Amiga specific)@{ub} The time zone database is by no means authoritative: governments change timekeeping rules erratically and sometimes with little warning, the data entries do not cover all of civil time before 1970, and undoubtedly errors remain in the code and data. Feel free to fill gaps or fix mistakes, and please email improvements to tz@iana.org for use in the future. To email small changes, please run a POSIX shell command like 'diff -u old/europe new/europe >myfix.patch', and attach myfix.patch to the email. For more-elaborate changes, please read the Theory file and browse the mailing list archives for examples of patches that tend to work well. Ideally, additions to data should contain commentary citing reliable sources as justification. Please submit changes against either the latest release in or the master branch of the experimental Git repository. If you use Git the following workflow may be helpful: * Copy the experimental repository. git clone https://github.com/eggert/tz.git cd tz * Get current with the master branch. git checkout master git pull * Switch to a new branch for the changes. Choose a different branch name for each change set. git checkout -b mybranch * Edit source files. Include commentary that justifies the changes by citing reliable sources. * Debug the changes, e.g.: make check make install ./zdump -v America/Los_Angeles * For each separable change, commit it in the new branch, e.g.: git add northamerica git commit See recent 'git log' output for the commit-message style. * Create patch files 0001-*, 0002-*, ... git format-patch master * After reviewing the patch files, send the patches to tz@iana.org for others to review. git send-email master * Start anew by getting current with the master branch again (the second step above). Please do not create issues or pull requests on GitHub, as the proper procedure for proposing and distributing patches is via email as illustrated above. @endnode @node TimeZone "TimeZone user manual" @title "TimeZone user manual" @{bg filltext}@{b}TimeZone TimeZone@{ub}@{bg background} @{b}NAME@{ub} TimeZone - select a time zone @{b}USAGE@{ub} TimeZone @{b}DESCRIPTION@{ub} TimeZone is used to set local time zone preferences. Time zone can be selected from a set of predefined zone files. The selected zone need to be located in the ZONEINFO: directory. The time zone name will be save to the TZ environment variable if selected. Do not choose this option if you already have a rule in your TZ variable. @endnode @node TimeZoneInfo "TimeZoneInfo user manual" @title "TimeZoneInfo user manual" @{bg filltext}@{b}TimeZoneInfo TimeZoneInfo@{ub}@{bg background} @{b}NAME@{ub} TimeZoneInfo - Show active time zone @{b}USAGE@{ub} TimeZoneInfo @{b}DESCRIPTION@{ub} TimeZoneInfo lists the most important properties of the active time zone. @endnode @node SetClockGMT "SetClockGMT user manual" @title "SetClockGMT user manual" @{bg filltext}@{b}SetClockGMT SetClockGMT@{ub}@{bg background} @{b}NAME@{ub} SetClockGMT - Set or read the battery backed-up hardware clock in GMT @{b}USAGE@{ub} SetClockGMT LOAD|SAVE|RESET @{b}DESCRIPTION@{ub} SetClockGMT SAVE sets the date and time of the battery backed-up hardware clock from the current system time and adjust it according to locale time zone. In order for SetClockGMT to operate correct, a local time zone need to be selected first. SetClockGMT LOAD sets the current system time in locale time zone from the battery backed-up clock. In systems using Kickstart 2.0 or later, the time is set automatically during the boot process. SetClockGMT LOAD need to executed after boot in order to active locale time zone. The RESET option resets the clock completely. This may be necessary if a poorly written program that does not follow the rules turns the clock off or sets the test bit of the clock. @endnode @node DSTCheck "DSTCheck user manual" @title "DSTCheck user manual" @{bg filltext}@{b}DSTCheck DSTCheck@{ub}@{bg background} @{b}NAME@{ub} DSTCheck - Warn when daylight saving time changes @{b}USAGE@{ub} DSTCheck @{b}DESCRIPTION@{ub} DSTCheck can be used in scripts to track when daylight saving time changes. @{b}EXAMPLE@{ub} DSTCheck IF WARN echo "### Summertime ###" ELSE echo "### Wintertime ###" ENDIF @endnode @node library "Timezone Library" @title "Timezone Library" @{b}timezone.library@{ub} Version 5 of the Timezone Library implements the following functions. time.h tzset, tzalloc, tzfree, time, mktime, mktime_z, localtime, localtime_r, localtime_rz, gmtime, gmtime_r, ctime, ctime_r, ctime_rz, difftime, offtime, offtime_r, timeoff, asctime, asctime_r, strftime, strftime_l, strptime, strptime_l, timegm, timelocal, timelocal_z, daylight_c, timezone_c, altzone_c, tzname_c, time2posix, time2posix_z, posix2time, posix2time_z, tzsetwall, tzgetname sys/time.h gettimeofday, settimeofday extra getsystime, setsystime, tzgetlocation, gmtoffset, stou, utos @endnode @node ZDump "ZDump user manual" @title "ZDump user manual" @{bg filltext}@{b}ZDump ZDump@{ub}@{bg background} @{b}NAME@{ub} ZDump - time zone dumper @{b}USAGE@{ub} ZDump [VERBOSE|VERBOSE2] [C=CUTOFF] [T=CUTOFFVERBOSE] { zonenames } @{b}DESCRIPTION@{ub} ZDump prints the current time in each zonename named on the command line. @{b}OPTIONS@{ub} VERBOSE For each zonename on the command line, print the time at the lowest possible time value, the time one day after the lowest possible time value, the times both one second before and exactly at each detected time discontinuity, the time at one day less than the highest possible time value, and the time at the highest possible time value. Each line is followed by isdst=D where D is positive, zero, or negative depending on whether the given time is daylight saving time, standard time, or an unknown time type, respectively. Each line is also followed by gmtoff=N if the given local time is known to be N seconds east of Greenwich. VERBOSE2 Like -v, except omit the times relative to the extreme time values. This generates output that is easier to compare to that of implementations with different time representations. CUTOFF [loyear,]hiyear Cut off verbose output at the given year(s). Cutoff times are computed using the proleptic Gregorian calendar with year 0 and with Universal Time (UT) ignoring leap seconds. The lower bound is exclusive and the upper is inclusive; for example, a loyear of 1970 excludes a transition occurring at 1970-01-01 00:00:00 UTC but a hiyear of 1970 includes the transition. The default cutoff is -500,2500. CUTOFFVERBOSE [lotime,]hitime Cut off verbose output at the given time(s), given in decimal seconds since 1970-01-01 00:00:00 Coordinated Universal Time (UTC). The zonename determines whether the count includes leap seconds. As with -c, the cutoff's lower bound is exclusive and its upper bound is inclusive. @{b}LIMITATIONS@{ub} Time discontinuities are found by sampling the results returned by localtime at twelve-hour intervals. This works in all real-world cases; one can construct artificial time zones for which this fails. In the output, "UT" denotes the value returned by gmtime, which uses UTC for modern time stamps and some other UT flavor for time stamps that predate the introduction of UTC. No attempt is currently made to have the output use "UTC" for newer and "UT" for older time stamps, partly because the exact date of the introduction of UTC is problematic. @{b}SEE ALSO@{ub} @{"tzfile" link "tzfile"}, @{"zic" link "zic"} @endnode @node zic "zic developer manual" @title "Time zone compiler" @{bg filltext}@{b}ZIC ZIC@{ub}@{bg background} @{b}NAME@{ub} zic - time zone compiler @{b}USAGE@{ub} zic [ option ... ] [ filename ... ] @{b}DESCRIPTION@{ub} Zic reads text from the file(s) named on the command line and creates the time conversion information files specified in this input. If a filename is "-", the standard input is read. @{b}OPTIONS@{ub} These options are available: --version Output version information and exit. -d directory Create time conversion information files in the named directory rather than in the standard directory named below. -l timezone Use the given time zone as local time. Zic will act as if the input contained a link line of the form Link timezone localtime -p timezone Use the given time zone's rules when handling POSIX-format time zone environment variables. Zic will act as if the input contained a link line of the form Link timezone posixrules -L leapsecondfilename Read leap second information from the file with the given name. If this option is not used, no leap second information appears in output files. -v Be more verbose, and complain about the following situations: The input specifies a link to a link. A year that appears in a data file is outside the range of years representable by time(2) values. A time of 24:00 or more appears in the input. Pre-1998 versions of zic prohibit 24:00, and pre-2007 versions prohibit times greater than 24:00. A rule goes past the start or end of the month. Pre-2004 versions of zic prohibit this. The output file does not contain all the information about the long-term future of a zone, because the future cannot be summarized as an extended POSIX TZ string. For example, as of 2013 this problem occurs for Iran's daylight-saving rules for the predicted future, as these rules are based on the Iranian calendar, which cannot be represented. The output contains data that may not be handled properly by client code designed for older zic output formats. These compatibility issues affect only time stamps before 1970 or after the start of 2038. A time zone abbreviation has fewer than 3 characters. POSIX requires at least 3. An output file name contains a byte that is not an ASCII letter, "-", "/", or "_"; or it contains a file name component that contains more than 14 bytes or that starts with "-". -s Limit time values stored in output files to values that are the same whether they're taken to be signed or unsigned. You can use this option to generate SVVS-compatible files. -y command Use the given command rather than yearistype when checking year types (see below). Input files should be text files, that is, they should be a series of zero or more lines, each ending in a newline byte and containing at most 511 bytes, and without any NUL bytes. The input text's encoding is typically UTF-8 or ASCII; it should have a unibyte representation for the POSIX Portable Character Set (PPCS) and the encoding's non- unibyte characters should consist entirely of non-PPCS bytes. Non-PPCS characters typically occur only in comments: although output file names and time zone abbreviations can contain nearly any character, other software will work better if these are limited to the restricted syntax described under the -v option. Input lines are made up of fields. Fields are separated from one another by one or more white space characters. The white space characters are space, form feed, carriage return, newline, tab, and vertical tab. Leading and trailing white space on input lines is ignored. An unquoted sharp character (#) in the input introduces a comment which extends to the end of the line the sharp character appears on. White space characters and sharp characters may be enclosed in double quotes (") if they're to be used as part of a field. Any line that is blank (after comment stripping) is ignored. Non-blank lines are expected to be of one of three types: rule lines, zone lines, and link lines. Names (such as month names) must be in English and are case insensitive. Abbreviations, if used, must be unambiguous in context. A rule line has the form Rule NAME FROM TO TYPE IN ON AT SAVE LETTER/S For example: Rule US 1967 1973 - Apr lastSun 2:00 1:00 D The fields that make up a rule line are: NAME Gives the (arbitrary) name of the set of rules this rule is part of. FROM Gives the first year in which the rule applies. Any integer year can be supplied; the proleptic Gregorian calendar is assumed. The word minimum (or an abbreviation) means the minimum year representable as an integer. The word maximum (or an abbreviation) means the maximum year representable as an integer. Rules can describe times that are not representable as time values, with the unrepresentable times ignored; this allows rules to be portable among hosts with differing time value types. TO Gives the final year in which the rule applies. In addition to minimum and maximum (as above), the word only (or an abbreviation) may be used to repeat the value of the FROM field. TYPE Gives the type of year in which the rule applies. If TYPE is "-" then the rule applies in all years between FROM and TO inclusive. If TYPE is something else, then zic executes the command yearistype year type to check the type of a year: an exit status of zero is taken to mean that the year is of the given type; an exit status of one is taken to mean that the year is not of the given type. IN Names the month in which the rule takes effect. Month names may be abbreviated. ON Gives the day on which the rule takes effect. Recognized forms include: 5 the fifth of the month lastSun the last Sunday in the month lastMon the last Monday in the month Sun>=8 first Sunday on or after the eighth Sun<=25 last Sunday on or before the 25th Names of days of the week may be abbreviated or spelled out in full. Note that there must be no spaces within the ON field. AT Gives the time of day at which the rule takes effect. Recognized forms include: 2 time in hours 2:00 time in hours and minutes 15:00 24-hour format time (for times after noon) 1:28:14 time in hours, minutes, and seconds - equivalent to 0 where hour 0 is midnight at the start of the day, and hour 24 is midnight at the end of the day. Any of these forms may be followed by the letter w if the given time is local "wall clock" time, s if the given time is local "standard" time, or u (or g or z) if the given time is universal time; in the absence of an indicator, wall clock time is assumed. The intent is that a rule line describes the instants when a clock/calendar set to the type of time specified in the AT field would show the specified date and time of day. SAVE Gives the amount of time to be added to local standard time when the rule is in effect. This field has the same format as the AT field (although, of course, the w and s suffixes are not used). LETTER/S Gives the "variable part" (for example, the "S" or "D" in "EST" or "EDT") of time zone abbreviations to be used when this rule is in effect. If this field is "-", the variable part is null. A zone line has the form Zone NAME GMTOFF RULES/SAVE FORMAT [UNTILYEAR [MONTH [DAY [TIME]]]] For example: Zone Australia/Adelaide 9:30 Aus AC%sT 1971 Oct 31 2:00 The fields that make up a zone line are: NAME The name of the time zone. This is the name used in creating the time conversion information file for the zone. It should not contain a file name component "." or ".."; a file name component is a maximal substring that does not contain "/". GMTOFF The amount of time to add to UT to get standard time in this zone. This field has the same format as the AT and SAVE fields of rule lines; begin the field with a minus sign if time must be subtracted from UT. RULES/SAVE The name of the rule(s) that apply in the time zone or, alternately, an amount of time to add to local standard time. If this field is - then standard time always applies in the time zone. FORMAT The format for time zone abbreviations in this time zone. The pair of characters %s is used to show where the "variable part" of the time zone abbreviation goes. Alternately, a slash (/) separates standard and daylight abbreviations. UNTILYEAR [MONTH [DAY [TIME]]] The time at which the UT offset or the rule(s) change for a location. It is specified as a year, a month, a day, and a time of day. If this is specified, the time zone information is generated from the given UT offset and rule change until the time specified, which is interpreted using the rules in effect just before the transition. The month, day, and time of day have the same format as the IN, ON, and AT fields of a rule; trailing fields can be omitted, and default to the earliest possible value for the missing fields. The next line must be a "continuation" line; this has the same form as a zone line except that the string "Zone" and the name are omitted, as the continuation line will place information starting at the time specified as the "until" information in the previous line in the file used by the previous line. Continuation lines may contain "until" information, just as zone lines do, indicating that the next line is a further continuation. A link line has the form Link TARGET LINK-NAME For example: Link Europe/Istanbul Asia/Istanbul The TARGET field should appear as the NAME field in some zone line. The LINK-NAME field is used as an alternate name for that zone; it has the same syntax as a zone line's NAME field. Except for continuation lines, lines may appear in any order in the input. However, the behavior is unspecified if multiple zone or link lines define the same name, or if the source of one link line is the target of another. Lines in the file that describes leap seconds have the following form: Leap YEAR MONTH DAY HH:MM:SS CORR R/S For example: Leap 1974 Dec 31 23:59:60 + S The YEAR, MONTH, DAY, and HH:MM:SS fields tell when the leap second happened. The CORR field should be "+" if a second was added or "-" if a second was skipped. The R/S field should be (an abbreviation of) "Stationary" if the leap second time given by the other fields should be interpreted as UTC or (an abbreviation of) "Rolling" if the leap second time given by the other fields should be interpreted as local wall clock time. @{b}EXTENDED EXAMPLE@{ub} Here is an extended example of zic input, intended to illustrate many of its features. # Rule NAME FROM TO TYPE IN ON AT SAVE LETTER/S Rule Swiss 1941 1942 - May Mon>=1 1:00 1:00 S Rule Swiss 1941 1942 - Oct Mon>=1 2:00 0 - Rule EU 1977 1980 - Apr Sun>=1 1:00u 1:00 S Rule EU 1977 only - Sep lastSun 1:00u 0 - Rule EU 1978 only - Oct 1 1:00u 0 - Rule EU 1979 1995 - Sep lastSun 1:00u 0 - Rule EU 1981 max - Mar lastSun 1:00u 1:00 S Rule EU 1996 max - Oct lastSun 1:00u 0 - # Zone NAME GMTOFF RULES/SAVE FORMAT UNTIL Zone Europe/Zurich 0:34:08 - LMT 1853 Jul 16 0:29:46 - BMT 1894 Jun 1:00 Swiss CE%sT 1981 1:00 EU CE%sT Link Europe/Zurich Switzerland In this example, the zone is named Europe/Zurich but it has an alias as Switzerland. This example says that Zurich was 34 minutes and 8 seconds west of UT until 1853-07-16 at 00:00, when the legal offset was changed to 7o26'22.50''; although this works out to 0:29:45.50, the input format cannot represent fractional seconds so it is rounded here. After 1894-06-01 at 00:00 Swiss daylight saving rules (defined with lines beginning with "Rule Swiss") apply, and the UT offset became one hour. From 1981 to the present, EU daylight saving rules have applied, and the UTC offset has remained at one hour. In 1941 and 1942, daylight saving time applied from the first Monday in May at 01:00 to the first Monday in October at 02:00. The pre-1981 EU daylight-saving rules have no effect here, but are included for completeness. Since 1981, daylight saving has begun on the last Sunday in March at 01:00 UTC. Until 1995 it ended the last Sunday in September at 01:00 UTC, but this changed to the last Sunday in October starting in 1996. For purposes of display, "LMT" and "BMT" were initially used, respectively. Since Swiss rules and later EU rules were applied, the display name for the time zone has been CET for standard time and CEST for daylight saving time. @{b}NOTES@{ub} For areas with more than two types of local time, you may need to use local standard time in the AT field of the earliest transition time's rule to ensure that the earliest transition time recorded in the compiled file is correct. If, for a particular zone, a clock advance caused by the start of daylight saving coincides with and is equal to a clock retreat caused by a change in UT offset, zic produces a single transition to daylight saving at the new UT offset (without any change in wall clock time). To get separate transitions use multiple zone continuation lines specifying transition instants using universal time. Time stamps well before the Big Bang are silently omitted from the output. This works around bugs in software that mishandles large negative time stamps. Call it sour grapes, but pre-Big-Bang time stamps are physically suspect anyway. The pre-Big-Bang cutoff time is approximate and may change in future versions. zic is currently not included in the Amiga distribution. @{b}FILE@{ub} ZONEINFO: - standard directory used for created files @{b}SEE ALSO@{ub} @{"tzfile" link "tzfile"}, @{"zdump" link "zdump"} @endnode @node tzfile "tzfile developer manual" @title "Time zone information" @{bg filltext}@{b}TZFILE TZFILE@{ub}@{bg background} @{b}NAME@{ub} tzfile - time zone information @{b}SYNOPSIS@{ub} #include @{b}DESCRIPTION@{ub} The time zone information files used by tzset begin with the magic characters "TZif" to identify them as time zone information files, followed by a character identifying the version of the file's format (as of 2013, either an ASCII NUL, or '2', or '3') followed by fifteen bytes containing zeroes reserved for future use, followed by six four- byte integer values 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 UT/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 entries are stored in the file. tzh_timecnt The number of transition times for which data entries are stored in the file. tzh_typecnt The number of local time types for which data entries are stored in the file (must not be zero). tzh_charcnt The number of characters of time zone abbreviation strings stored in the file. The above header is followed by tzh_timecnt four-byte signed integer values sorted in ascending order. These values are written in standard byte order. Each is used as a transition time (as returned by time) at which the rules for computing local time change. Next come tzh_timecnt one-byte unsigned integer values; 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 appears next in the file; these structures are defined as follows: struct ttinfo { int32_t tt_gmtoff; unsigned char tt_isdst; unsigned char tt_abbrind; }; Each structure is written as a four-byte signed integer value for tt_gmtoff, 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 UT, 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) 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 UT/local indicators, each stored as a one-byte value; they tell whether the transition times associated with local time types were specified as UT or local time, and are used when a time zone file is used in handling POSIX-style time zone environment 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. For version-2-format time zone 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. 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). For version-3-format time zone files, the POSIX-TZ-style string may use two minor extensions to the POSIX TZ format, as described in 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. Future changes to the format may append more data. @{b}SEE ALSO@{ub} @{"zdump" link "zdump"}, @{"zic" link "zic"} @endnode