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NAME
zic - timezone compiler
SYNOPSIS
zic [ option ... ] [ filename ... ]
DESCRIPTION
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.
OPTIONS
--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This feature is obsolete and poorly supported.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 “-”.
FILES
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.
EXTENDED EXAMPLE
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.
FILES
/etc/localtime
Default local timezone file.
/usr/share/zoneinfo
Default timezone information directory.
NOTES
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.
SEE ALSO
tzfile(5), zdump(8)
COLOPHON
This page is part of release 5.10 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)