ZIC(8)

NAME
zic - time zone compiler

SYNOPSIS
zic [ option ... ] [ filename ... ]

DESCRIPTION
Zic 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 the standard input is read.

These options are available:

--version
    Output version information and exit.

-d directory
    Create time conversion information files in the named directory rather than in the standard directory named below.

-l timezone
    Use the given time zone as local time. Zic will act as if the input contained a link line of the form

    Link    timezone    localtime

-p timezone
    Use the given time zone's rules when handling POSIX-format time zone environment variables. Zic will act as if the input contained a link line of the form

    Link    timezone    posixrules

-t file
    When creating local time information, put the configuration link in the named file rather than in the standard location.

-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 zone, 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 time stamps 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. Non-blank 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	2:00	1:00	D

The fields that make up a rule line are:

NAME
    Gives the (arbitrary) name of the set of rules this rule is part of.

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 (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
    00:19:32.13	time with fractional 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. 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 time, s if the given time is local 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 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. Only the sum of standard time and this amount matters; 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 (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

Zone	NAME	GMTOFF	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 time zone. This is the name used in creating the time conversion information file for the zone. It should not contain a file name component or a file name component is a maximal substring that does not contain

GMTOFF
    The amount of time to add to UT to get standard time in this zone. 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 time zone or, alternately, an amount of time to add to local standard time. If this field is - then standard time always applies in the time zone. When an amount of time is given, only the sum of standard time and this amount matters.

FORMAT
    The format for time zone abbreviations in this time zone. The pair of characters %s is used to show where the of the time zone abbreviation goes. Alternately, 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. Alternately, 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 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. 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 alternate 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) 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.

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	GMTOFF	RULES	FORMAT	[UNTIL]
Zone	Europe/Zurich	0:34:08	-	LMT	1853 Jul 16
		0:29:46	-	BMT	1894 Jun
		1:00	Swiss	CE%sT	1981
		1:00	EU	CE%sT

Link	Europe/Zurich	Europe/Vaduz

In this example, the zone 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 display name for the time zone has been CET for standard time and CEST for daylight saving time.

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 zone, 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.

Time stamps well before the Big Bang are silently omitted from the output. This works around bugs in software that mishandles large negative time stamps. Call it sour grapes, but pre-Big-Bang time stamps are physically suspect anyway. The pre-Big-Bang cutoff time is approximate and may change in future versions.

FILES
/etc/localtime    default local time zone file
/usr/share/zoneinfo    default time zone information directory

SEE ALSO
newctime(3), tzfile(5), zdump(8)