zic(8) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | OPTIONS | FILES | EXTENDED EXAMPLE | FILES | NOTES | SEE ALSO | COLOPHON

ZIC(8)                   Linux System Administration                  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 time conversion information files specified in this
       input.  If a filename is “-”, standard input is read.

OPTIONS         top

       --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.  Although the
              default is currently fat, this is intended to change in future
              zic versions, as software that mishandles the 64-bit data
              typically mishandles timestamps after the year 2038 anyway.
              Also see the -r option for another way to shrink 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

       -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

              This feature is obsolete and poorly supported.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]
              Reduce the size of output files by limiting their
              applicability 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.  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.  Also see the
              -b slim option for another way to shrink output size.

       -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.

              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 TZ string.  For example, as of
              2019 this problem occurs for Iran's daylight-saving rules for
              the predicted future, as these rules are based on the Iranian
              calendar, which cannot be represented.

              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 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         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 511 bytes, 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) ⟨http://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    TYPE  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.  The word
               minimum (or an abbreviation) means the indefinite past.  The
               word maximum (or an abbreviation) means the indefinite
               future.  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.  In addition
               to minimum and maximum (as above), the word only (or an
               abbreviation) may be used to repeat the value of the FROM
               field.

       TYPE    should be “-” and is present for compatibility with older
               versions of zic in which it could contain year types.

       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; 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 of the amount of time to be added to local
             standard time effect, 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 “-”.

       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.

       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.
       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.

       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, or if the source of one link line is the
       target of another.

       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.

       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; zic outputs this
       expiration timestamp by truncating the end of the output file to the
       timestamp.  If there is no expiration line, zic also accepts a
       comment “#expires E ...” where E is the expiration timestamp as a
       decimal integer count of seconds since the Epoch, not counting leap
       seconds.  However, the “#expires” comment is an obsolescent feature,
       and the leap second file should use an expiration line instead of
       relying on a comment.

EXTENDED EXAMPLE         top

       Here is an extended example of zic input, intended to illustrate many
       of its features.  In this example, the EU rules are for the European
       Union and for its predecessor organization, the European Communities.

         # Rule  NAME  FROM  TO    TYPE  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 timezone is named Europe/Zurich but it has an
       alias as 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°26′22.50″, 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         top

       /etc/localtime
              Default local timezone file.

       /usr/share/zoneinfo
              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)

COLOPHON         top

       This page is part of release 5.08 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at
       https://www.kernel.org/doc/man-pages/.

                                 2020-08-13                           ZIC(8)

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