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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.

       -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

       -p timezone
              Use  timezone's  rules  when  handling POSIX-format timezone 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 timezone, 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 timestamps
              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.

       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    TYPE  IN   ON       AT     SAVE   LETTER/S

       For example:

            Rule  US    1967  1973  -     Apr  lastSun  2:00w  1:00   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.

       TYPE    should be “-” and is present for compatibility with older versions of zic in which
               it could contain year types.

       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.  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
                    01:28:14     time in hours, minutes, and seconds
                    15:00        24-hour format time (for times after noon)
                    260:00       260 hours after 00:00
                    -2:30        2.5 hours before 00:00
                    -            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).  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        UTOFF  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 “/”.

       UTOFF
            The amount of time to add to UT to get standard time.  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 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.  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.

       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.

       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  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.

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    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           UTOFF    RULES  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  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″; 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 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 wall clock time).  To get separate transitions use  multiple  zone  continuation  lines
       specifying transition instants using universal time.

SEE ALSO

       tzfile(5), zdump(8)

COLOPHON

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       project, information about reporting bugs, and the latest version of  this  page,  can  be
       found at https://www.kernel.org/doc/man-pages/.

                                            2019-03-06                                     ZIC(8)