zic

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 time conversion information 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              This feature is obsolete and poorly supported.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]
              Reduce the size of output files by limiting their applicability 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.  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 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) ⟨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.  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 of
             the amount of time to be added to local standard time effect, 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 “-”.

       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.

       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; zic outputs this expiration timestamp
       by truncating the end of the output file to the timestamp.  If there is
       no expiration line, zic also accepts a comment “#expires E ...” where E
       is the expiration timestamp as a decimal integer count of seconds since
       the Epoch, not counting leap seconds.  However, the “#expires” comment is
       an obsolescent feature, and the leap second file should use an expiration
       line instead of relying on a comment.

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°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)