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              Unless timezone is “-”, this option is obsolete and poorly supported.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