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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 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

              If timezone is “-” (the default), any already-existing link is removed.

              Unless timezone is “-”, this option is obsolete and  poorly  supported.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.

       -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.  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.   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.1-2017 TZ string.  Also see the -b slim option for another way to shrink output size.

       -R @hi Generate redundant trailing explicit transitions for timestamps that occur less  than  hi  seconds
              since  the Epoch, even though the transitions could be more concisely represented via the extended
              POSIX.1-2017 TZ string.  This option does not affect  the  represented  timestamps.   Although  it
              accommodates  nonstandard  TZif  readers  that  ignore  the  extended  POSIX.1-2017  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, something not supported by some older parsers, including zic
              itself through release 2022e.

              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.1-2017 TZ string.  For example, as of
              2023  this  problem  occurs  for  Morocco's  daylight-saving  rules,  as  these rules are based on
              predictions for when Ramadan will be observed, something that an extended POSIX.1-2017  TZ  string
              cannot represent.

              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 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)  ⟨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.  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.  The word maximum (or an abbreviation) means the
              indefinite future, and 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, 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 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 or as the LINK-NAME field in some link
       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.  Links can chain together, although the behavior is unspecified if a chain of one or
       more links does not terminate in a Zone name.  A link line can appear before the line  that  defines  the
       link target.  For example:

         Link  Greenwich  G_M_T
         Link  Etc/GMT    Greenwich
         Zone  Etc/GMT  0  -  GMT

       The two links are chained together, and G_M_T, Greenwich, and Etc/GMT all name the same zone.

       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.

       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.

         # 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  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 degrees 26 minutes 22.50 seconds, 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)