|ZIC(8)||System Manager's Manual||ZIC(8)|
Link timezone localtime
Link timezone posixrules
This feature is obsolete and poorly supported. Among other things it should not be used for timestamps after the year 2037, and it should not be combined with -b slim if timezone's transitions are at standard time or Universal Time (UT) instead of local time.
The input specifies a link to a link.
A year that appears in a data file is outside the range of representable years.
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.
A time zone abbreviation uses a %z format. Pre-2015 versions of zic do not support this.
A timestamp contains fractional seconds. Pre-2018 versions of zic do not support this.
The input contains abbreviations that are mishandled by pre-2018 versions of zic due to a longstanding coding bug. These abbreviations include “L” for “Link”, “mi” for “min”, “Sa” for “Sat”, and “Su” for “Sun”.
The output file does not contain all the information about the long-term future of a timezone, because the future cannot be summarized as an extended POSIX TZ string. For example, as of 2019 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 timestamps before 1970 or after the start of 2038.
The output file contains more than 1200 transitions, which may be mishandled by some clients. The current reference client supports at most 2000 transitions; pre-2014 versions of the reference client support at most 1200 transitions.
A time zone abbreviation has fewer than 3 or more than 6 characters. POSIX requires at least 3, and requires implementations to support at least 6.
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 “-”.
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) ⟨http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap06.html⟩ 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. Nonblank lines are expected to be of one of three types: rule lines, zone lines, and link lines.
Names must be in English and are case insensitive. They appear in several contexts, and include month and weekday names and keywords such as maximum, only, Rolling, and Zone. A name can be abbreviated by omitting all but an initial prefix; any abbreviation 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 2:00w 1:00d DThe fields that make up a rule line are:
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
A weekday name (e.g., Sunday) or a weekday name preceded by “last” (e.g., lastSunday) may be abbreviated or spelled out in full. There must be no white space characters within the ON field. The “<=” and “>=” constructs can result in a day in the neighboring month; for example, the IN-ON combination “Oct Sun>=31” stands for the first Sunday on or after October 31, even if that Sunday occurs in November.
2 time in hours 2:00 time in hours and minutes 01:28:14 time in hours, minutes, and seconds 00:19:32.13 time with fractional seconds 12:00 midday, 12 hours after 00:00 15:00 3 PM, 15 hours after 00:00 24:00 end of day, 24 hours after 00:00 260:00 260 hours after 00:00 -2:30 2.5 hours before 00:00 - equivalent to 0
Although zic rounds times to the nearest integer second (breaking ties to the even integer), the fractions may be useful to other applications requiring greater precision. The source format does not specify any maximum precision. Any of these forms may be followed by the letter w if the given time is local or “wall clock” time, s if the given time is standard time without any adjustment for daylight saving, or u (or g or z) if the given time is universal time; in the absence of an indicator, local (wall clock) time is assumed. These forms ignore leap seconds; for example, if a leap second occurs at 00:59:60 local time, “1:00” stands for 3601 seconds after local midnight instead of the usual 3600 seconds. 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.
A zone line has the form
Zone NAME STDOFF RULES FORMAT [UNTIL] For example: Zone Asia/Amman 2:00 Jordan EE%sT 2017 Oct 27 01:00The fields that make up a zone line are:
If a zone changes at the same instant that a rule would otherwise take effect in the earlier zone or continuation line, the rule is ignored. A zone or continuation line L with a named rule set starts with standard time by default: that is, any of L's timestamps preceding L's earliest rule use the rule in effect after L's first transition into standard time. In a single zone it is an error if two rules take effect at the same instant, or if two zone changes take effect at the same instant.
A link line has the form
Link TARGET LINK-NAME For example: Link Europe/Istanbul Asia/IstanbulThe TARGET field should appear as the NAME field in some zone line. The LINK-NAME field is used as an alternative 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.
The file that describes leap seconds can have leap lines and an expiration line. Leap lines have the following form:
Leap YEAR MONTH DAY HH:MM:SS CORR R/S For example: Leap 2016 Dec 31 23:59:60 + SThe 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.
The expiration line, if present, has the form:
Expires YEAR MONTH DAY HH:MM:SS For example: Expires 2020 Dec 28 00:00:00The YEAR, MONTH, DAY, and HH:MM:SS fields give the expiration timestamp in UTC for the leap second table; zic outputs this expiration timestamp by truncating the end of the output file to the timestamp. If there is no expiration line, zic also accepts a comment “#expires E ...” where E is the expiration timestamp as a decimal integer count of seconds since the Epoch, not counting leap seconds. However, the “#expires” comment is an obsolescent feature, and the leap second file should use an expiration line instead of relying on a comment.
In this example, the timezone is named Europe/Zurich but it has an alias as Europe/Vaduz. This example says that Zurich was 34 minutes and 8 seconds east of UT until 1853-07-16 at 00:00, when the legal offset was changed to 7°26′22.50″, which works out to 0:29:45.50; zic treats this by rounding it to 0:29:46. After 1894-06-01 at 00:00 the UT offset became one hour and Swiss daylight saving rules (defined with lines beginning with “Rule Swiss”) apply. From 1981 to the present, EU daylight saving rules have applied, and the UTC offset has remained at one hour.
# 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 STDOFF RULES FORMAT [UNTIL] Zone Europe/Zurich 0:34:08 - LMT 1853 Jul 16 0:29:45.50 - BMT 1894 Jun 1:00 Swiss CE%sT 1981 1:00 EU CE%sT Link Europe/Zurich Europe/Vaduz
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 time zone abbreviation has been CET for standard time and CEST for daylight saving time.
If, for a particular timezone, 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 local (wall clock) time. To get separate transitions use multiple zone continuation lines specifying transition instants using universal time.