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

NAME
       zic - timezone compiler

SYNOPSIS
       zic [ option ... ] [ filename ... ]

DESCRIPTION
       The zic program reads text from the file(s) named on the command line
       and creates the timezone information format (TZif) files specified in
       this input.  If a filename is "-", standard input is read.

OPTIONS
       --version
              Output version information and exit.

       --help Output short usage message and exit.

       -b bloat
              Output  backward-compatibility  data  as specified by bloat.  If
              bloat is fat, generate additional data entries that work  around
              potential  bugs  or incompatibilities in older software, such as
              software that mishandles the 64-bit generated data.  If bloat is
              slim, keep the output files small; this can help check  for  the
              bugs  and  incompatibilities.   The default is slim, as software
              that mishandles  64-bit  data  typically  mishandles  timestamps
              after  the year 2038 anyway.  Also see the -r option for another
              way to alter output size.

       -d directory
              Create time conversion information files in the named  directory
              rather than in the standard directory named below.

       -l timezone
              Use  timezone  as  local  time.   zic  will  act as if the input
              contained a link line of the form

                Link  timezone  localtime

              If timezone is -, any already-existing link is removed.

       -L leapsecondfilename
              Read leap second information from the file with the given  name.
              If  this  option is not used, no leap second information appears
              in output files.

       -p timezone
              Use timezone's rules when handling nonstandard TZ  strings  like
              "EET-2EEST"  that lack transition rules.  zic will act as if the
              input contained a link line of the form

                Link  timezone  posixrules

              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              Unless  timezone  is  "-",  this  option  is obsolete and poorly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)

Time Zone Database                                                      zic(8)