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ZIC(8) System Manager's Manual ZIC(8)
NAME
zic - timezone compiler
SYNOPSIS
zic [--version] [--help] [-b] [-d directory] [-L leapsecondfilename]
[-l localtime] [-p posixrules] [-s] [-t file] [-v] [-y command]
[file ...]
DESCRIPTION
The 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.
Options
--version Output version information and exit.
--help Output short usage message and exit.
-b bloat Output backward-compatibility data as specified by bloat. If
bloat is `fat', 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
Create time conversion information files in the named
directory rather than in the standard directory named below.
-l timezone
Use the timezone as local time. zic 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
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.
-p timezone
Use timezone's rules when handling POSIX-format TZ strings
like `EET-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Unless timezone is `-', this option is obsolete and poorly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]]
Limit the applicability of output files to timestamps in the
range from lo (inclusive) to hi (exclusive), where lo and hi
are possibly signed decimal counts of seconds since the Epoch
(1970-01-01 00:00:00 UTC). Omitted counts default to extreme
values. The output files use UT offset 0 and abbreviation
`-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 Generate redundant trailing explicit transitions for
timestamps that occur less than hi seconds since the Epoch,
even though the transitions could be more concisely
represented via the extended POSIX TZ string. This option
does not affect the represented timestamps. Although it
accommodates nonstandard TZif readers that ignore the
extended POSIX TZ string, it increases the size of the
altered output files.
-t file When creating local time information, put the configuration
link in the named file rather than in the standard location.
-v Be more verbose, and complain about the following situations:
- The input specifies a link to a link, something not
supported by some older parsers, including zic itself
through release 2022e.
- 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 2023 this problem occurs for
Morocco's daylight-saving rules, as on predictions for
when Ramadan will be observed, something that an extended
POSIX TZ string cannot represent.
- 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 contains a truncated leap second table, which
can cause some older TZif readers to misbehave. This can
occur if the -L option is used, and either an `Expires'
line is present or the -r option is also used.
- 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 `-'.
Zone description file format
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
2048 bytes counting the newline, 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)
(https://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 - 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:
NAME Gives the name of the rule set that contains this line.
The name must start with a character that is neither an
ASCII digit nor `-' nor `+'. To allow for future
extensions, an unquoted name should not contain characters
from the set `!$%&'()*,/:;<=>?@[\]^`{|}~'.
FROM Gives the first year in which the rule applies. Any signed
integer year can be supplied; the proleptic Gregorian
calendar is assumed, with year 0 preceding year 1. The
word `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.
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.
- should always be `-' 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.
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. 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.
AT Gives the time of day at which the rule takes effect,
relative to 00:00, the start of a calendar day. Recognized
forms include:
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.
SAVE Gives the amount of time to be added to local standard time
when the rule is in effect, and whether the resulting time
is standard or daylight saving. This field has the same
format as the AT field, except with a different set of
suffix letters: `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.
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 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:
NAME The name of the timezone. This is the name used in
creating the time conversion information file for the
timezone. It should not contain a file name component `.'
or `..'; a file name component is a maximal substring that
does not contain `/'.
STDOFF The amount of time to add to UT to get standard time,
without any adjustment for daylight saving. This field has
the same format as the AT and SAVE fields of rule lines,
except without suffix letters; begin the field with a minus
sign if time must be subtracted from UT.
RULES The name of the rules that apply in the timezone or,
alternatively, a field in the same format as a rule-line
SAVE column, giving the amount of time to be added to local
standard time and whether the resulting time is standard or
daylight saving. If this field is `-' then standard time
always applies. When an amount of time is given, only the
sum of standard time and this amount matters.
FORMAT The format for time zone abbreviations. The pair of
characters `%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.
UNTIL The time at which the UT offset or the rule(s) change for a
location. It takes the form of one to four fields YEAR
[MONTH [DAY [TIME]]]. 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.
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 second file format
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
+ 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.
EXTENDED EXAMPLE
Here is an extended example of 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<degree>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.
FILES
Input files use the format described in this section; output files use
tzfile(5) format.
/etc/localtime Default local timezone file
/usr/share/zoneinfo Default timezone information directory
NOTES
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 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.
SEE ALSO
tzfile(5), zdump(8)
NetBSD 10.99 December 6, 2023 NetBSD 10.99