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ZIC(8) |
FreeBSD System Manager's Manual |
ZIC(8) |
zic |
[--help ] [--version ]
[-Dsv ] [-b
slim | fat]
[-d directory]
[-g gid]
[-l localtime]
[-L leapseconds]
[-m mode]
[-p posixrules]
[-r
[@lo][/@hi]]
[-R
-@ hi]
[-t localtime-link]
[-u uid]
[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.
The following options are available:
--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
- Do not create directories.
-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. The
zic utility will act as if the input contained a
link line of the form
If timezone is
‘- ’, any already-existing link is
removed.
-L
filename
- 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. The
zic utility will act as if the input contained a
link line of the form
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this option is obsolete and poorly supported.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,
-r
-@0 omits data intended for negative timestamps
(i.e., before the Epoch), and -r
-@0/@2147483648 outputs data intended only for
nonnegative timestamps that fit into 31-bit signed integers. 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.
- 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. 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
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°26′22.50″, 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.
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