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NAME | SYNOPSIS | DESCRIPTION | OPTIONS | FILES | EXTENDED EXAMPLE | FILES | NOTES | SEE ALSO | COLOPHON |
ZIC(8) Linux System Administration 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 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. Although the
default is currently fat, this is intended to change in future
zic versions, as software that mishandles the 64-bit data
typically mishandles timestamps after the year 2038 anyway.
Also see the -r option for another way to shrink 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
-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
This feature is obsolete and poorly supported.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.
-r [@lo][/@hi]
Reduce the size of output files by limiting their
applicability 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 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. 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 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 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 zic 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 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 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 1:00d 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 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. 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; 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 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.
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.
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.
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; 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 TYPE 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 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″, 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 release 5.08 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/.
2020-08-13 ZIC(8)
Pages that refer to this page: tzfile(5) , tzselect(8) , zdump(8)
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