zic — timezone compiler
zic
[option...]
[filename...]
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.
−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
−p
timezone
Use timezone
's rules when
handling POSIX-format timezone environment variables.
zic will
act as if the input contained a link line of the
form
Link timezone
posixrules
−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.
−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 years representable by time(2) values.
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.
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 2013 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 zic output formats. These compatibility issues affect only timestamps before 1970 or after the start of 2038.
A time zone abbreviation has fewer than 3 characters. POSIX requires at least 3.
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 -.
−s
Limit time values stored in output files to values that are the same whether they're taken to be signed or unsigned. You can use this option to generate SVVS-compatible files.
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 typically UTF-8 or ASCII; it
should have a unibyte representation for the POSIX Portable
Character Set (PPCS) <http://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 TYPE IN ON AT SAVE LETTER/S
For example:
Rule US 1967 1973 - Apr lastSun 2:00w 1:00 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.
TYPE
should be - and is present for compatibility with older versions of zic in which it could contain year types.
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
A weekday name (e.g., Sunday) or a weekday
name preceded by last (e.g.,
lastSunday) may be
abbreviated or spelled out in full. Note that there
must be no spaces within the ON
field.
AT
Gives the time of day at which the rule takes effect. Recognized forms include:
2
- time in hours
2:00
- time in hours and minutes
01:28:14
- time in hours, minutes, and seconds
15:00
- 24-hour format time (for times after noon)
260:00
- 260 hours after 00:00
-2:30
- 2.5 hours before 00:00
-
- equivalent to 0
where hour 0 is midnight at the start of the day,
and hour 24 is midnight at the end of the day. Any of
these forms may be followed by the letter w
if the given time is local
wall clock time,
s
if the given time is
local standard time, or
u
(or g
or z
)
if the given time is universal time; in the absence of
an indicator, wall clock time is assumed. 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. This field
has the same format as the AT
field (although, of course, the
w
and s
suffixes are not used). 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
.
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 UTOFF 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 /
.
UTOFF
The amount of time to add to UT to get standard
time. 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, alternatively, a field in the same format as a rule-line SAVE column, giving of the amount of time to be added to local standard 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
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 -.
UNTIL
The time at which the UT offset or the rule(s) change for a location. It takes the form of 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. 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
For example:
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 target of another.
Lines in the file that describes leap seconds 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.
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
Rule
- Swiss
Rule
- Swiss
Rule
- EU
Rule
- EU
Rule
- EU
Rule
- EU
Rule
- EU
Rule
- EU
# Zone
- NAME
Zone
- Europe/Zurich
Link
- Europe/Zurich
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 seconds east of UT until 1853-07-16 at 00:00, when the legal offset was changed to 7°26′22.50″; although this works out to 0:29:45.50, the input format cannot represent fractional seconds so it is rounded here. 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 wall clock time). To get separate transitions use multiple zone continuation lines specifying transition instants using universal time.
This page is part of release 5.04 of the Linux man-pages
project. A
description of the project, information about reporting bugs,
and the latest version of this page, can be found at
https://www.kernel.org/doc/man−pages/.
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