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

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 timezone information format (TZif) 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.  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 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 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              This feature is obsolete and poorly supported.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.

              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 "-00"
              in place of the omitted timestamp data; this typically reduces
              the files' sizes.  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 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 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) <https://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    -  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.

       -       Is a reserved field and should always contain "-" 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
               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 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 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.

       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  [UNTIL]
         Zone  America/Menominee  -5:00   -      EST     1973 Apr 29 2:00
                                  -6:00   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;

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    -  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<degree>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)

                                                                        ZIC(8)
