zic(8) — Linux manual page


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

NAME         top

       zic - timezone compiler

SYNOPSIS         top

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

DESCRIPTION         top

       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

OPTIONS         top

              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

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              Unless timezone is “-”, this option is obsolete and poorly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

       -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

              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

              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

              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         top

       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.

              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

       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

         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.


       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

       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         top

              Default local timezone file.

              Default timezone information directory.

NOTES         top

       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         top

       tzfile(5), zdump(8)

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Time Zone Database                                                zic(8)

Pages that refer to this page: tzfile(5)tzselect(8)zdump(8)