zic(8) |
System Manager's Manual |
zic(8) |
The 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 is standard input is read. Output version
information and exit. Output short usage message and exit. Output
backward-compatibility data as specified by If is 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 is
keep the output files small; this can help check for the bugs and
incompatibilities. The default is as software that mishandles 64-bit data
typically mishandles timestamps after the year 2038 anyway. Also see the
option for another way to alter output size. Create time conversion
information files in the named directory rather than in the standard directory
named below. Use the as local time. will act as if the input contained a link
line of the form If 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 rules when handling
POSIX-format TZ strings like that lack transition rules. will act as if the
input contained a link line of the form This feature is obsolete and poorly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 if transitions are at standard
time or Universal Time (UT) instead of local time. If is any already-existing
link is removed. Limit the applicability of output files to timestamps in the
range from (inclusive) to (exclusive), where and 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
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 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 causes a TZif file to contain explicit entries for
transitions rather than concisely representing them with an extended POSIX TZ
string. Also see the option for another way to shrink output size. Generate
redundant trailing explicit transitions for timestamps that occur less than Ar
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. When creating local time information, put the
configuration link in the named file rather than in the standard location. 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 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 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 prohibit this. A time zone abbreviation uses a format.
Pre-2015 versions of do not support this. A timestamp contains fractional
seconds. Pre-2018 versions of do not support this. The input contains
abbreviations that are mishandled by pre-2018 versions of due to a
longstanding coding bug. These abbreviations include for for for and for 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 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 option is used, and
either an Expires line is present or the 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 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 2048 bytes
counting the newline, and without any 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) 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 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 and 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 For example: The fields that make up a rule
line are: 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 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 (or an abbreviation) means the indefinite past. The
word (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. Gives the final year in which the rule applies. In addition
to and (as above), the word (or an abbreviation) may be used to repeat the
value of the field. should be for compatibility with older versions of It was
previously known as the field, which could contain values to allow a separate
script to further restrict in which of years the rule would apply. Names the
month in which the rule takes effect. Month names may be abbreviated. Gives
the day on which the rule takes effect. Recognized forms include: the fifth of
the month the last Sunday in the month the last Monday in the month first
Sunday on or after the eighth 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.,
or a weekday name preceded by (e.g., may be abbreviated or spelled out in
full. There must be no white space characters within the field. The and
constructs can result in a day in the neighboring month; for example, the
IN-ON combination tands for the first Sunday on or after October 31, even if
that Sunday occurs in November. Gives the time of day at which the rule takes
effect, relative to 00:00, the start of a calendar day. Recognized forms
include: time in hours time in hours and minutes time in hours, minutes, and
seconds time with fractional seconds midday, 12 hours after 00:00 3 PM, 15
hours after 00:00 end of day, 24 hours after 00:00 260 hours after 00:00 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 if the given time is local or time, if the given time is standard
time without any adjustment for daylight saving, or (or or 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 field
would show the specified date and time of day. 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 field for standard time and for daylight saving time. The suffix letter
is typically omitted, and defaults to if the offset is zero and to 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, does not distinguish
a 10:30 standard time plus an 0:30 from a 10:00 standard time plus a 1:00
Gives the (for example, the or in or 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 For example: The fields that make up a zone line are:
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 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 and
fields of rule lines, except without suffix letters; begin the field with a
minus sign if time must be subtracted from UT. 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. The format for time
zone abbreviations. The pair of characters is used to show where the of the
time zone abbreviation goes. Alternatively, a format can use the pair of
characters +to stand for the UT offset in the form or using the shortest form
that does not lose information, where and 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 is a placeholder that means local time is unspecified. 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 line; this has the same form as a zone line except that the string
and the name are omitted, as the continuation line will place information
starting at the time specified as the information in the previous line in the
file used by the previous line. Continuation lines may contain 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 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 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
seconds is instead assumed to take effect simultaneously. For example: 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, interprets this more
sensibly as a single transition from 02:00 CST (-05) to 02:00 CDT (-05). A
link line has the form For example: The field should appear as the field in
some zone line. field in some zone line or as the field in some link line. The
field is used as an alternative name for that zone; it has the same syntax as
a zone line's 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: 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: For
example: The and fields tell when the leap second happened. The field should
be if a second was added or if a second was skipped. The field should be (an
abbreviation of) if the leap second time given by the other fields should be
interpreted as UTC or (an abbreviation of) 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 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 option is used. The
expiration line, if present, has the form: For example: The and fields give
the expiration timestamp in UTC for the leap second table. Here is an extended
example of 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. 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; 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 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 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, and 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.
Input files use the format described in this section; output files use format.
Default local timezone file Default timezone information directory For areas
with more than two types of local time, you may need to use local standard
time in the 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, 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.