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

     zic - timezone compiler

     zic [--version] [--help] [-b] [-d directory] [-L leapsecondfilename]
         [-l localtime] [-p posixrules] [-s] [-t file] [-v] [-y command]
         [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.

     --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 directory
                 Create time conversion information files in the named
                 directory rather than in the standard directory named below.
     -l timezone
                 Use the timezone as local time.  zic will act as if the input
                 contained a link line of the form
                       Link timezone  localtime
                 If timezone is -, any already-existing link is removed.
     -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 POSIX-format 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                 This feature is obsolete and poorly supported.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.  If timezone is -, any already-
                 existing link is removed.
     -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 in
                 place of the omitted timestamp data.  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.  Or using date(1),

                 zic -r @$(date +%s)
                 omits data intended for past timestamps.  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 an extended POSIX TZ string.
                 Also see the -b slim option for another way to shrink output
     -R @hi      Generate redundant trailing explicit transitions for
                 timestamps that occur less than Ar hi seconds since the
                 Epoch, even though the transitions could be more concisely
                 represented via the extended POSIX TZ string.  This option
                 does not affect the represented timestamps.  Although it
                 accommodates nonstandard TZif readers that ignore the
                 extended POSIX 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.

                 -   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(8) 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 or it contains a file
                     name component that contains more than 14 bytes or that
                     starts with "-".

     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)
     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

     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

     -         should be "-" 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

                     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

               Names of days of the week may be abbreviated or spelled out in
               full.  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" tands 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

                     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 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,
               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 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/SAVE     FORMAT    [UNTIL]

     For example:

           Zone Asia/Amman     2:00 Jordan    EE%sT     2017 Oct 27 1:00

     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
                 column, giving the amount of time to be added to local
                 standard time 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
                 "-".  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

                 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 with a named rule set starts with standard time
     by default: that is, any of timestamps preceding earliest rule use the
     rule in effect after 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
           Zone   America/Menominee
                             -    EST
                                    1973 Apr 29 2:00
                                        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

           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.

     Rolling leap seconds were implemented back when it was not clear whether
     common practice was rolling or stationary, with concerns that one would
     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.  However, this countdown style does not
     seem to have caught on, which means rolling leap seconds are not used in
     practice; also, they 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/SAVE 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<degree>26'22.50''; which
     this 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 From 1981
     to the present, EU daylight saving rules have

     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

     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.

     Input files use the format described in this section; output files use
     tzfile(5) format.
     /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)

NetBSD 9.99                     August 24, 2022                    NetBSD 9.99