ZIC(8)                      System Manager's Manual                     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

       -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.

       -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) <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 (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

            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 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.

       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    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.

       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

               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.

       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
                    15:00    24-hour format time (for times after noon)
                    1:28:14  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.

       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 w and s suffixes are not
               used).

       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                GMTOFF  RULES/SAVE  FORMAT  [UNTILYEAR [MONTH [DAY [TIME]]]]

       For example:

            Zone  Australia/Adelaide  9:30    Aus         AC%sT   1971 Oct 31  2:00

       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/SAVE
             The name of the rule(s) 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.

       FORMAT
             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.  Alternately, a slash (/)
             separates standard and daylight abbreviations.

       UNTILYEAR [MONTH [DAY [TIME]]]
             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

            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  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.

EXTENDED EXAMPLE
       Here is an extended example of zic input, intended to illustrate many
       of its features.

         # 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/SAVE  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  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 7o26'22.50''; 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.

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.

FILE
       /usr/local/etc/zoneinfo        standard directory used for created
       files

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

                                                                        ZIC(8)
