Manual browser: zic(8)

ZIC(8) System Manager's Manual ZIC(8)


zictime zone compiler


zic [--version] [-d directory] [-L leapsecondfilename] [-l localtime] [-p posixrules] [-s] [-v] [-y command] [Filename ...]


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:

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 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.
-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
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.
Be more verbose, and complain about the following situations:
  • Pre-1998 versions of zic(8) prohibit 24:00, and pre-2007 versions prohibit times greater than 24:00.
  • Pre-2004 versions of zic(8) prohibit this.
  • 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.
  • code designed for older zic(8) output formats. These compatibility issues affect only time stamps before 1970 or after the start of 2038.
  • POSIX requires at least 3.
  • “-”, “/”, or “_”; or it or it contains a file name component that contains more than 14 bytes or that starts with “-”.
-y command
Use the given command rather than yearistype when checking year types (see below).

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) 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 (such as month names) must be in English and are case insensitive. Abbreviations, if used, must be unambiguous in context.

A rule line has the form

For example:
Rule US 1967 1973 - Apr lastSun 2:00 1:00 D
The fields that make up a rule line are:
Gives the (arbitrary) name of the set of rules this rule is part of.
Gives the first year in which the rule applies. Any integer year can be supplied; the proleptic Gregorian calendar is assumed. The word minimum (or an abbreviation) means the minimum year representable as an integer. The word maximum (or an abbreviation) means the maximum year representable as an integer. 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.
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.
Gives the type of year in which the rule applies. If TYPE is - then the rule applies in all years between FROM and TO inclusive. If TYPE is something else, then zic executes the command

yearistype year type

to check the type of a year: an exit status of zero is taken to mean that the year is of the given type; an exit status of one is taken to mean that the year is not of the given type.

Names the month in which the rule takes effect. Month names may be abbreviated.
Gives the day on which the rule takes effect. Recognized forms include:
the fifth of the month
the last Sunday in the month
the last Monday in the month
first Sunday on or after the eighth
last Sunday on or before the 25th
Names of days of the week may be abbreviated or spelled out in full. Note that there must be no spaces within the ON field.
Gives the time of day at which the rule takes effect. Recognized forms include:
time in hours
time in hours and minutes
24-hour format time (for times after noon)
time in hours, minutes, and seconds
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.
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).
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

For example:
Zone Australia/Adelaide 9:30 Aus AC%sT 1971 Oct 31 2:00
The fields that make up a zone line are:
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 “/”.
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.
The name of the rule(s) that apply in the time zone or, alternatively, an amount of time to add to local standard time. If this field is - then standard time always applies in the time zone.
The format for time zone abbreviations in this time zone. The pair of characters %s is used to show where the “variable part” of the time zone abbreviation goes. Alternatively, a slash (/) separates standard and daylight abbreviations.
The time at which the UT offset or the rule(s) change for a location. It is specified as a year, a month, a day, and a time of day. If this is specified, the time zone information is generated from the given UT offset and rule change until the time specified. 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.

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. 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:

For example:
Leap 1974 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.
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 Europe/Zurich 0:34:08 - LMT 1853 Jul 16
0:29:44 - BMT 1894 Jun
1:00 Swiss CE%sT 1981
1:00 EU CE%sT
Link Europe/Zurich Switzerland

In this example, the zone is named Europe/Zurich but it has an alias as Switzerland. This example says that Zurich was 34 minutes and 8 seconds west 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 Swiss daylight saving rules (defined with lines beginning with "Rule Swiss") apply, and the UT offset became one hour. 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.


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.


/usr/share/zoneinfo - standard directory used for created files
October 6, 2014 NetBSD 7.0