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 a TZif file's 64-bit data or proleptic
              TZ string.  If bloat is slim, keep the output files small; this
              can help check for the bugs and incompatibilities.  The default
              is slim, as the fat workarounds are typically good only until
              the year 2038 anyway.  Also see the -r option for another way to
              alter output size.

       -D     Do not create ancestor directories of output files, For example,
              for a zone named America/Los_Angeles the directory America
              should already exist.  By default, the directory and its
              ancestors are created if they do not already exist.  -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; this is required by some TZif readers.

       -p timezone
              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              Unless timezone is “-”, this option is obsolete and is no longer
              supported by most runtimes.  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.  The option
              is present only to support obsolete runtimes that used
              timezone's rules when handling obsolescent TZ strings like
              "AST4ADT" that lack transition rules; modern runtimes that
              support these TZ strings typically just use current US rules as
              the TZ strings were mainly used in the US.  Similarly, any Zone
              or Link named "posixrules" is obsolete and problematic.

       -m mode
              Create TZif files with the given file mode bits.  By default the
              files are created with mode 644 as modified by the umask.  With
              this option they are created with the given mode instead.  For
              portability the mode should be an unsigned octal integer,
              typically 644 or 444; some platforms also support chmod(1)-style
              symbolic modes.  This option does not affect created ancestor
              directories, which have mode 755 as modified by the umask.  The
              option is ignored on platforms lacking the notion of file mode
              bits.

       -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.

       -u owner[:group]
              Change the output regular files' owner and group to those
              specified.  The owner is either a user name, or an unsigned
              decimal integer user ID, or an empty string meaning no change to
              the owner.  The group is similar for group names and IDs.  This
              option does not affect directories or hard or symbolic links.
              It typically needs special privileges to change ownership, and
              is ignored on platforms that lack the notions of owners and
              groups.

       -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) 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) according
       to the “until” value in the zone line, and the second an hour later
       from 02:00 CST (-06) to 03:00 CDT (-05) according to the values in the
       April rule line.  However, zic interprets this more sensibly as a
       single transition from 02:00 EST (-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.

SEE ALSO
       tzfile(5), zdump(8)

Time Zone Database                                                      zic(8)
