# zic

## 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 a proleptic 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 proleptic TZ string.  This option does
                  not affect the represented timestamps.  Although it
                  accommodates nonstandard TZif readers that ignore the
                  proleptic 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 a proleptic 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 a proleptic 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 as mentioned previously; for
                  example, January can appear as “January”, “JANU” or “Ja”,
                  but not as “j” which would be ambiguous with both June and
                  July.
    
           **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 as mentioned
                  previously, e.g., “Su” for Sunday and “lastsa” for the last
                  Saturday.  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** field, giving the amount of time to be added to local
                  standard time and whether the resulting time is standard or
                  daylight saving.  Standard time applies if this field is **-**
                  or for timestamps occurring before any rule takes effect.
                  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** shows where to put the time zone
                  abbreviation's variable part, which is taken from the
                  **LETTER/S** field of the corresponding rule; any timestamps
                  that precede the earliest rule use the **LETTER/S** of the
                  earliest standard-time rule (which in this case must
                  exist).  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 would let one 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.  Although stationary leap seconds are
           the common practice, rolling leap seconds can be useful in
           specialized applications like SMPTE timecodes that may prefer to
           put leap second discontinuities at the end of a local broadcast
           day.  However, rolling leap seconds 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.
    


* * *