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NAME | SYNOPSIS | DESCRIPTION | OPTIONS | FILES | EXTENDED EXAMPLE | FILES | NOTES | SEE ALSO | COLOPHON |
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zic(8) System Manager's Manual zic(8)
zic - timezone compiler
zic [ option ... ] [ filename ... ]
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 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 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 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 nonstandard 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
If timezone is “-” (the default), any already-existing link
is removed.
Unless timezone is “-”, this option is obsolete and poorly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.
-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. On
platforms with GNU date, “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 a proleptic 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 proleptic TZ string. This option does
not affect the represented timestamps. Although it
accommodates nonstandard TZif readers that ignore the
proleptic 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 a proleptic TZ string. For
example, as of 2023 this problem occurs for Morocco's
daylight-saving rules, as these rules are based on
predictions for when Ramadan will be observed, something
that a proleptic 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 “-”.
Input files use the format described in this section; output files
use tzfile(5) 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. 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. The word
maximum (or an abbreviation) means the indefinite future,
and the word only (or an abbreviation) may be used to
repeat the value of the FROM field.
- Is a reserved field and should always contain “-” 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 as mentioned previously; for
example, January can appear as “January”, “JANU” or “Ja”,
but not as “j” which would be ambiguous with both June and
July.
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
A weekday name (e.g., Sunday) or a weekday name preceded by
“last” (e.g., lastSunday) may be abbreviated as mentioned
previously, e.g., “Su” for Sunday and “lastsa” for the last
Saturday. 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 FORMAT [UNTIL]
For example:
Zone Asia/Amman 2:00 Jordan EE%sT 2017 Oct 27 01:00
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 field, giving the amount of time to be added to local
standard time and whether the resulting time is standard or
daylight saving. Standard time applies if this field is -
or for timestamps occurring before any rule takes effect.
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 shows where to put the time zone
abbreviation's variable part, which is taken from the
LETTER/S field of the corresponding rule; any timestamps
that precede the earliest rule use the LETTER/S of the
earliest standard-time rule (which in this case must
exist). 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.
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 would let one 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. Although stationary leap seconds are
the common practice, rolling leap seconds can be useful in
specialized applications like SMPTE timecodes that may prefer to
put leap second discontinuities at the end of a local broadcast
day. However, rolling leap seconds 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.
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 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 degrees 26 minutes 22.50 seconds, 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.
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.
/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 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.
tzfile(5), zdump(8)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
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⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
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Time Zone Database zic(8)
Pages that refer to this page: tzfile(5), tzselect(8), zdump(8)
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