ZIC(8) | System Manager's Manual | ZIC(8) |
zic
—
zic |
[- -version ]
[- -help ]
[-b ] [-d
directory] [-L
leapsecondfilename] [-l
localtime] [-p
posixrules] [-s ]
[-t file]
[-v ] [-y
command] [file ...] |
zic
program reads text from the file(s) named on the
command line and creates the timezone information format (TZif) files
specified in this input. If a file is
‘-
’, standard input is read.
-
-version
-
-help
-b
bloatfat
’, generate additional data
entries that work around potential bugs or incompatibilities in older
software, such as software that mishandles the 64-bit generated data. If
bloat is
‘slim
’, keep the output files small;
this can help check for the bugs and incompatibilities. The default is
‘slim
’, as software that mishandles
64-bit data typically mishandles timestamps after the year 2038 anyway.
Also see the -r
option for another way to alter
output size.-d
directory-l
timezonezic
will act as if the input contained a link line
of the form
Link
timezone localtime
If timezone is
‘-
’, any already-existing link is
removed.
-L
leapsecondfilename-p
timezoneEET-2EEST
’ that lack
transition rules. zic
will act as if the input
contained a link line of the form
Link
timezone posixrules
Unless timezone is
‘-
’, this option is obsolete and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. If
timezone is
‘-
’, any already-existing link is
removed.
-r
[@
lo[/@
hi]]-00
’ in place of the omitted
timestamp data. For example,
zic -r @0
omits data intended for negative timestamps (i.e., before the Epoch), and
zic -r
@0/@2147483648
outputs data intended only for nonnegative timestamps that fit into 31-bit signed integers. Or using date(1),
zic -r @$(date +%s)
omits data intended for past timestamps. Although this option
typically reduces the output file's size, the size can increase due to
the need to represent the timestamp range boundaries, particularly if
hi causes a TZif file to contain explicit entries
for pre-hi transitions
rather than concisely representing them with an extended POSIX TZ
string. Also see the -b
slim
option for another way to shrink output
size.
-R
@
hi-t
file-v
zic
itself through
release 2022e.zic
prohibit 24:00, and pre-2007 versions
prohibit times greater than 24:00.zic
prohibit this.%z
’ format. Pre-2015 versions
of zic
do not support this.zic
do not support this.zic
due to a longstanding coding
bug. These abbreviations include
‘L
’ for
‘Link
’,
‘mi
’ for
‘min
’,
‘Sa
’ for
‘Sat
’, and
‘Su
’ for
‘Sun
’.zic
output formats.
These compatibility issues affect only timestamps before 1970 or after
the start of 2038.-L
option is used, and either an
‘Expires
’ line is present or the
-r
option is also used.-
’,
‘/
’, or
‘_
’; or it contains a file name
component that contains more than 14 bytes or that starts with
‘-
’.-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 | - | IN | ON | AT | SAVE | LETTER/S |
For example:
Rule | US | 1967 | 1973 | - | Apr | lastSun | 2:00w | 1:00d | D |
The fields that make up a rule line are:
-
’ nor
‘+
’. To allow for future extensions,
an unquoted name should not contain characters from the set
‘!$%&'()*,/:;<=>?@[\]^`{|}~
’.minimum
’
(or an abbreviation) means the indefinite past. The word
‘maximum
’ (or an abbreviation) means
the indefinite future. 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.minimum
’ and
‘maximum
’ (as above), the word
‘only
’ (or an abbreviation) may be
used to repeat the value of the FROM field.-
-
’ for
compatibility with older versions of zic
. It was
previously known as the TYPE field, which could
contain values to allow a separate script to further restrict in which
“types” of years the rule would apply.Names of days of the week may be abbreviated or spelled out in
full. 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
2:00
01:28:14
00:19:32.13
12:00
15:00
24:00
260:00
-2:30
-
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.
s
’ for standard time and
‘d
’ for daylight saving time. The
suffix letter is typically omitted, and defaults to
‘s
’ if the offset is zero and to
‘d
’ otherwise. Negative offsets are
allowed; in Ireland, for example, daylight saving time is observed in
winter and has a negative offset relative to Irish Standard Time. The
offset is merely added to standard time; for example,
zic
does not distinguish a 10:30 standard time
plus an 0:30 SAVE from a 10:00 standard time plus a
1:00 SAVE.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 | STDOFF | RULES/SAVE | FORMAT | [UNTIL] |
For example:
Zone | Asia/Amman | 2:00 | Jordan | EE%sT | 2017 Oct 27 1:00 |
The fields that make up a zone line are:
.
’ or
‘..
’; a file name component is a
maximal substring that does not contain
‘/
’.-
’ then standard time always
applies. When an amount of time is given, only the sum of standard time
and this amount matters.%s
’ is used to show where the
“variable part” of the time zone abbreviation goes.
Alternatively, a format can use the pair of characters
‘%z
’ to stand for the UT offset in
the form ±hh, ±hhmm, or
±hhmmss, using the shortest form that does not
lose information, where hh, mm, and
ss are the hours, minutes, and seconds east (+) or west
(-) of UT. Alternatively, a slash
(‘/
’) separates standard and
daylight abbreviations. To conform to POSIX, a time zone abbreviation
should contain only alphanumeric ASCII characters,
‘+
’ and
‘-
’. By convention, the time zone
abbreviation ‘-00
’ is a placeholder
that means local time is unspecified.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.
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.
If a continuation line subtracts N seconds from the UT offset after a transition that would be interpreted to be later if using the continuation line's UT offset and rules, the UNTIL time of the previous zone or continuation line is interpreted according to the continuation line's UT offset and rules, and any rule that would otherwise take effect in the next N seconds is instead assumed to take effect simultaneously. For example:
# Rule | NAME | FROM | TO | - | IN | ON | AT | SAVE | LETTER/S |
Rule | US | 1967 | 2006 | - | Oct | lastSun | 2:00 | 0 | S |
Rule | US | 1967 | 1973 | - | Apr | lastSun | 2:00 | 1:00 | D |
# Zone | NAME | STDOFF | RULES | FORMAT | [UNTIL] |
Zone | America/Menominee | -5:00 | - | EST | 1973 Apr 29 2:00 |
-6:00 | US | C%sT |
Here, an incorrect reading would be there were two clock changes
on 1973-04-29, the first from 02:00 EST (-05) to 01:00 CST (-06), and the
second an hour later from 02:00 CST (-06) to 03:00 CDT (-05). However,
zic
interprets this more sensibly as a single
transition from 02:00 CST (-05) to 02:00 CDT (-05).
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 or as the LINK-NAME field in some link 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. Links can chain together, although the behavior is unspecified if a chain of one or more links does not terminate in a Zone name. A link line can appear before the line that defines the link target. For example:
Link | Greenwich | G_M_T |
Link | Etc/GMT | Greenwich |
Zone | Etc/GMT 0 | - GMT |
The two links are chained together, and G_M_T, Greenwich, and Etc/GMT all name the same zone.
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.
Leap | YEAR | MONTH | DAY | HH:MM:SS | CORR | R/S |
For example:
Leap | 2016 | 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.
Rolling leap seconds were implemented back when it was not clear
whether common practice was rolling or stationary, with concerns that one
would see Times Square ball drops where there'd be a “3... 2... 1...
leap... Happy New Year” countdown, placing the leap second at
midnight New York time rather than midnight UTC. However, this countdown
style does not seem to have caught on, which means rolling leap seconds are
not used in practice; also, they are not supported if the
-r
option is used.
The expiration line, if present, has the form:
Expires | YEAR | MONTH | DAY | HH:MM:SS |
For example:
Expires | 2020 | Dec | 28 | 00:00:00 |
The YEAR, MONTH, DAY, and HH:MM:SS fields give the expiration timestamp in UTC for the leap second table.
zic
input, intended to
illustrate many of its features.
# Rule | NAME | FROM | TO | - | 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/SAVE | 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 this example, the EU rules are for the European Union and for
its predecessor organization, the European Communities. The timezone is
named Europe/Zurich and it has the alias 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 this 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.
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.
December 6, 2023 | NetBSD 10.1 |