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ZIC(8) NetBSD System Manager's Manual ZIC(8)
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zic -- timezone compiler
zic [--version] [--help] [-b] [-d directory] [-L leapsecondfilename]
[-l localtime] [-p posixrules] [-s] [-t file] [-v] [-y command]
The zic program 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 -, standard input is read.
--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 Also
see the -r option for another way to alter output size.
Create time conversion information files in the named direc-
tory rather than in the standard directory named below.
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.
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.
Use timezone's rules when handling POSIX-format TZ strings
like "EET2EEST" that lack transition rules. zic will act as
if the input contained a link line of the form
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This feature is obsolete and poorly supported.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. If timezone is , any already-
existing link is removed.
-r [@lo / [@hi]]
Reduce the size of output files by limiting their applicabil-
ity 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. For example,
zic -r @0
omits data intended for negative timestamps (i.e., before the
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. Also see the -b
slim option for another way to shrink output size.
-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.
- 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 ver-
sions of zic do not support this.
- A timestamp contains fractional seconds. Pre-2018 ver-
sions 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 can-
not be represented.
- The output contains data that may not be handled properly
by client code designed for older zic(8) 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
- 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 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 typi-
cally 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. Lead-
ing 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 charac-
ters 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 sev-
eral 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
A rule line has the form
Rule NAME FROM TO - IN ON AT SAVE LETTER/S
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 por-
table 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 abbrevia-
tion) may be used to repeat the value of the FROM field.
- should 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
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 pre-
ceded 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 com-
bination "Oct Sun>=31" tands 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
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 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,
"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 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]
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; 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, alterna-
tively, a field in the same format as a rule-line SAVE col-
umn, giving of the amount of time to be added to local stan-
dard time effect, 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 charac-
ters %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. Alterna-
tively, a slash (/) separates standard and daylight abbrevia-
tions. To conform to POSIX, a time zone abbreviation should
contain only alphanumeric ASCII characters, "+" and "-".
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
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 pre-
vious line. Continuation lines may contain until informa-
tion, 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 with a named rule set starts with standard time
by default: that is, any of timestamps preceding earliest rule use the
rule in effect after 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
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 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 tar-
get of another.
The file that describes leap seconds can have leap lines and an expira-
tion line. Leap lines have the following form:
Leap YEAR MONTH DAY HH:MM:SS CORR R/S
Leap 2016 Dec 31 23:59:60 + S
The YEAR, MONTH, DAY, and HH:MM:SS fields tell when the leap second hap-
pened. 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
The expiration line, if present, has the form:
Expires YEAR MONTH DAY HH:MM:SS
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 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.
Here is an extended example of zic input, intended to illustrate many of
its features. In this example, the EU rules are for the European Union
and for its predecessor organization, the European Communities.
# 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 timezone is named Europe/Zurich but it has an alias
as Europe/Vaduz. This example says that Zurich was 34 minutes and 8 sec-
onds 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 From 1981 to the present, EU daylight saving rules have
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 complete-
ness. 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, respec-
tively. Since Swiss rules and later EU rules were applied, the time zone
abbreviation has been CET for standard time and CEST for daylight saving
Input files use the format described in this section; output files use
/etc/localtime Default local timezone file
/usr/share/zoneinfo Default timezone information directory
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 sav-
ing at the new UT offset without any change in local (wall clock) time.
To get separate transitions use multiple zone continuation lines specify-
ing transition instants using universal time.
NetBSD 9.99 October 9, 2020 NetBSD 9.99