1ZIC(8)                    Linux System Administration                   ZIC(8)
2
3
4

NAME

6       zic - timezone compiler
7

SYNOPSIS

9       zic [ option ... ] [ filename ... ]
10

DESCRIPTION

12       The  zic  program reads text from the file(s) named on the command line
13       and creates the time conversion information files specified in this in‐
14       put.  If a filename is “-”, standard input is read.
15

OPTIONS

17       --version
18              Output version information and exit.
19
20       --help Output short usage message and exit.
21
22       -b bloat
23              Output  backward-compatibility  data  as specified by bloat.  If
24              bloat is fat, generate additional data entries that work  around
25              potential  bugs  or incompatibilities in older software, such as
26              software that mishandles the 64-bit generated data.  If bloat is
27              slim,  keep  the output files small; this can help check for the
28              bugs and incompatibilities.  Although the default  is  currently
29              fat, this is intended to change in future zic versions, as soft‐
30              ware that mishandles the 64-bit data typically mishandles  time‐
31              stamps  after  the year 2038 anyway.  Also see the -r option for
32              another way to shrink output size.
33
34       -d directory
35              Create time conversion information files in the named  directory
36              rather than in the standard directory named below.
37
38       -l timezone
39              Use  timezone  as local time.  zic will act as if the input con‐
40              tained a link line of the form
41
42                   Link  timezone  localtime
43
44       -L leapsecondfilename
45              Read leap second information from the file with the given  name.
46              If  this  option is not used, no leap second information appears
47              in output files.
48
49       -p timezone
50              Use timezone's rules when handling nonstandard TZ  strings  like
51              "EET-2EEST"  that lack transition rules.  zic will act as if the
52              input contained a link line of the form
53
54                   Link  timezone  posixrules
55
56              This feature is obsolete  and  poorly  supported.   Among  other
57              things it should not be used for timestamps after the year 2037,
58              and it should not be combined with -b slim if timezone's transi‐
59              tions are at standard time or Universal Time (UT) instead of lo‐
60              cal time.
61
62       -r [@lo][/@hi]
63              Reduce the size of output files by limiting their  applicability
64              to  timestamps  in  the  range from lo (inclusive) to hi (exclu‐
65              sive), where lo and hi are  possibly-signed  decimal  counts  of
66              seconds  since  the  Epoch  (1970-01-01  00:00:00 UTC).  Omitted
67              counts default to extreme values.   For  example,  “zic  -r  @0”
68              omits  data  intended  for negative timestamps (i.e., before the
69              Epoch), and “zic -r @0/@2147483648” outputs data  intended  only
70              for nonnegative timestamps that fit into 31-bit signed integers.
71              On platforms with GNU date, “zic -r @$(date +%s)” omits data in‐
72              tended for past timestamps.  Also see the -b slim option for an‐
73              other way to shrink output size.
74
75       -t file
76              When creating local time information, put the configuration link
77              in the named file rather than in the standard location.
78
79       -v     Be more verbose, and complain about the following situations:
80
81              The input specifies a link to a link.
82
83              A  year that appears in a data file is outside the range of rep‐
84              resentable years.
85
86              A time of 24:00 or more appears in the input.  Pre-1998 versions
87              of  zic  prohibit  24:00,  and  pre-2007 versions prohibit times
88              greater than 24:00.
89
90              A rule goes past the start or end of the month.   Pre-2004  ver‐
91              sions of zic prohibit this.
92
93              A time zone abbreviation uses a %z format.  Pre-2015 versions of
94              zic do not support this.
95
96              A timestamp contains fractional seconds.  Pre-2018  versions  of
97              zic do not support this.
98
99              The input contains abbreviations that are mishandled by pre-2018
100              versions of zic due to a longstanding coding bug.  These  abbre‐
101              viations include “L” for “Link”, “mi” for “min”, “Sa” for “Sat”,
102              and “Su” for “Sun”.
103
104              The output file does not contain all the information  about  the
105              long-term  future  of  a  timezone, because the future cannot be
106              summarized as an extended POSIX TZ string.  For example,  as  of
107              2019  this  problem  occurs for Iran's daylight-saving rules for
108              the predicted future, as these rules are based  on  the  Iranian
109              calendar, which cannot be represented.
110
111              The  output  contains  data  that may not be handled properly by
112              client code designed for older zic output formats.   These  com‐
113              patibility  issues  affect  only timestamps before 1970 or after
114              the start of 2038.
115
116              The output file contains more than 1200 transitions,  which  may
117              be  mishandled  by  some  clients.  The current reference client
118              supports at most 2000 transitions; pre-2014 versions of the ref‐
119              erence client support at most 1200 transitions.
120
121              A time zone abbreviation has fewer than 3 or more than 6 charac‐
122              ters.  POSIX requires at least 3, and  requires  implementations
123              to support at least 6.
124
125              An output file name contains a byte that is not an ASCII letter,
126              “-”, “/”, or “_”; or it contains a file name component that con‐
127              tains more than 14 bytes or that starts with “-”.
128

FILES

130       Input  files use the format described in this section; output files use
131       tzfile(5) format.
132
133       Input files should be text files, that is, they should be a  series  of
134       zero  or  more  lines,  each ending in a newline byte and containing at
135       most 511 bytes, and without any NUL bytes.  The input  text's  encoding
136       is  typically  UTF-8  or ASCII; it should have a unibyte representation
137       for the POSIX Portable Character Set (PPCS) ⟨http://pubs.opengroup.org/
138       onlinepubs/9699919799/basedefs/V1_chap06.html⟩  and the encoding's non-
139       unibyte characters should consist entirely of non-PPCS bytes.  Non-PPCS
140       characters typically occur only in comments: although output file names
141       and time zone abbreviations can contain  nearly  any  character,  other
142       software will work better if these are limited to the restricted syntax
143       described under the -v option.
144
145       Input lines are made up of fields.  Fields are separated from  one  an‐
146       other  by  one or more white space characters.  The white space charac‐
147       ters are space, form feed, carriage return, newline, tab, and  vertical
148       tab.   Leading  and trailing white space on input lines is ignored.  An
149       unquoted sharp character (#) in the input introduces  a  comment  which
150       extends  to  the end of the line the sharp character appears on.  White
151       space characters and sharp characters may be enclosed in double  quotes
152       (")  if  they're to be used as part of a field.  Any line that is blank
153       (after comment stripping) is ignored.  Nonblank lines are  expected  to
154       be of one of three types: rule lines, zone lines, and link lines.
155
156       Names must be in English and are case insensitive.  They appear in sev‐
157       eral contexts, and include month and weekday names and keywords such as
158       maximum,  only,  Rolling, and Zone.  A name can be abbreviated by omit‐
159       ting all but an initial prefix; any abbreviation must be unambiguous in
160       context.
161
162       A rule line has the form
163
164            Rule  NAME  FROM  TO    TYPE  IN   ON       AT     SAVE   LETTER/S
165
166       For example:
167
168            Rule  US    1967  1973  -     Apr  lastSun  2:00w  1:00d  D
169
170       The fields that make up a rule line are:
171
172       NAME    Gives  the  name  of the rule set that contains this line.  The
173               name must start with a character that is neither an ASCII digit
174               nor  “-”  nor “+”.  To allow for future extensions, an unquoted
175               name   should   not   contain   characters   from    the    set
176               “!$%&'()*,/:;<=>?@[\]^`{|}~”.
177
178       FROM    Gives the first year in which the rule applies.  Any signed in‐
179               teger year can be supplied; the proleptic Gregorian calendar is
180               assumed, with year 0 preceding year 1.  The word minimum (or an
181               abbreviation) means the indefinite past.  The word maximum  (or
182               an  abbreviation)  means  the indefinite future.  Rules can de‐
183               scribe times that are not representable as  time  values,  with
184               the unrepresentable times ignored; this allows rules to be por‐
185               table among hosts with differing time value types.
186
187       TO      Gives the final year in which the rule applies.  In addition to
188               minimum  and maximum (as above), the word only (or an abbrevia‐
189               tion) may be used to repeat the value of the FROM field.
190
191       TYPE    should be “-” and is present for compatibility with older  ver‐
192               sions of zic in which it could contain year types.
193
194       IN      Names  the  month  in which the rule takes effect.  Month names
195               may be abbreviated.
196
197       ON      Gives the day on which the rule takes effect.  Recognized forms
198               include:
199
200                    5        the fifth of the month
201                    lastSun  the last Sunday in the month
202                    lastMon  the last Monday in the month
203                    Sun>=8   first Sunday on or after the eighth
204                    Sun<=25  last Sunday on or before the 25th
205
206               A  weekday  name  (e.g.,  Sunday) or a weekday name preceded by
207               “last” (e.g., lastSunday) may be abbreviated or spelled out  in
208               full.   There  must  be no white space characters within the ON
209               field.  The “<=” and “>=” constructs can result in a day in the
210               neighboring  month;  for  example,  the  IN-ON combination “Oct
211               Sun>=31” stands for the first Sunday on or  after  October  31,
212               even if that Sunday occurs in November.
213
214       AT      Gives  the time of day at which the rule takes effect, relative
215               to 00:00, the start of a calendar day.   Recognized  forms  in‐
216               clude:
217
218                    2            time in hours
219                    2:00         time in hours and minutes
220                    01:28:14     time in hours, minutes, and seconds
221                    00:19:32.13  time with fractional seconds
222                    12:00        midday, 12 hours after 00:00
223                    15:00        3 PM, 15 hours after 00:00
224                    24:00        end of day, 24 hours after 00:00
225                    260:00       260 hours after 00:00
226                    -2:30        2.5 hours before 00:00
227                    -            equivalent to 0
228
229               Although zic rounds times to the nearest integer second (break‐
230               ing ties to the even integer), the fractions may be  useful  to
231               other  applications  requiring  greater  precision.  The source
232               format does not specify any maximum precision.   Any  of  these
233               forms  may be followed by the letter w if the given time is lo‐
234               cal or “wall clock” time, s if the given time is standard  time
235               without any adjustment for daylight saving, or u (or g or z) if
236               the given time is universal time; in the absence of an  indica‐
237               tor,  local  (wall  clock) time is assumed.  These forms ignore
238               leap seconds; for example, if a leap second occurs at  00:59:60
239               local time, “1:00” stands for 3601 seconds after local midnight
240               instead of the usual 3600 seconds.  The intent is that  a  rule
241               line  describes  the  instants when a clock/calendar set to the
242               type of time specified in the AT field would show the specified
243               date and time of day.
244
245       SAVE    Gives  the  amount  of  time to be added to local standard time
246               when the rule is in effect, and whether the resulting  time  is
247               standard or daylight saving.  This field has the same format as
248               the AT field except with a different set of suffix  letters:  s
249               for  standard  time and d for daylight saving time.  The suffix
250               letter is typically omitted, and defaults to s if the offset is
251               zero and to d otherwise.  Negative offsets are allowed; in Ire‐
252               land, for example, daylight saving time is observed  in  winter
253               and has a negative offset relative to Irish Standard Time.  The
254               offset is merely added to standard time; for example, zic  does
255               not  distinguish a 10:30 standard time plus an 0:30 SAVE from a
256               10:00 standard time plus a 1:00 SAVE.
257
258       LETTER/S
259               Gives the “variable part” (for example, the “S” or “D” in “EST”
260               or  “EDT”) of time zone abbreviations to be used when this rule
261               is in effect.  If this field is “-”, the variable part is null.
262
263       A zone line has the form
264
265            Zone  NAME        STDOFF  RULES   FORMAT  [UNTIL]
266
267       For example:
268
269            Zone  Asia/Amman  2:00    Jordan  EE%sT   2017 Oct 27 01:00
270
271       The fields that make up a zone line are:
272
273       NAME  The name of the timezone.  This is the name used in creating  the
274             time conversion information file for the timezone.  It should not
275             contain a file name component “.” or “..”; a file name  component
276             is a maximal substring that does not contain “/”.
277
278       STDOFF
279             The amount of time to add to UT to get standard time, without any
280             adjustment for daylight saving.  This field has the  same  format
281             as  the  AT and SAVE fields of rule lines; begin the field with a
282             minus sign if time must be subtracted from UT.
283
284       RULES The name of the rules that apply in  the  timezone  or,  alterna‐
285             tively,  a  field  in the same format as a rule-line SAVE column,
286             giving of the amount of time to be added to local  standard  time
287             effect,  and  whether  the resulting time is standard or daylight
288             saving.  If this field is - then standard  time  always  applies.
289             When  an  amount  of time is given, only the sum of standard time
290             and this amount matters.
291
292       FORMAT
293             The format for time zone abbreviations.  The pair  of  characters
294             %s is used to show where the “variable part” of the time zone ab‐
295             breviation goes.  Alternatively, a format can  use  the  pair  of
296             characters  %z to stand for the UT offset in the form ±hh, ±hhmm,
297             or ±hhmmss, using the shortest form that does not  lose  informa‐
298             tion,  where  hh,  mm, and ss are the hours, minutes, and seconds
299             east (+) or west (−) of UT.  Alternatively, a slash (/) separates
300             standard and daylight abbreviations.  To conform to POSIX, a time
301             zone abbreviation should contain only alphanumeric ASCII  charac‐
302             ters, “+” and “-”.
303
304       UNTIL The time at which the UT offset or the rule(s) change for a loca‐
305             tion.  It takes the form of one to four fields YEAR  [MONTH  [DAY
306             [TIME]]].   If  this  is  specified, the time zone information is
307             generated from the given UT offset and rule change until the time
308             specified,  which  is  interpreted using the rules in effect just
309             before the transition.  The month, day, and time of day have  the
310             same  format  as  the  IN,  ON, and AT fields of a rule; trailing
311             fields can be omitted, and default to the earliest possible value
312             for the missing fields.
313
314             The  next  line  must be a “continuation” line; this has the same
315             form as a zone line except that the string “Zone”  and  the  name
316             are  omitted,  as  the  continuation  line will place information
317             starting at the time specified as the “until” information in  the
318             previous  line  in the file used by the previous line.  Continua‐
319             tion lines may contain “until” information, just  as  zone  lines
320             do, indicating that the next line is a further continuation.
321
322       If  a zone changes at the same instant that a rule would otherwise take
323       effect in the earlier zone or continuation line, the rule  is  ignored.
324       A  zone  or continuation line L with a named rule set starts with stan‐
325       dard time by default: that is, any of L's timestamps preceding L's ear‐
326       liest rule use the rule in effect after L's first transition into stan‐
327       dard time.  In a single zone it is an error if two rules take effect at
328       the  same  instant,  or if two zone changes take effect at the same in‐
329       stant.
330
331       A link line has the form
332
333            Link  TARGET           LINK-NAME
334
335       For example:
336
337            Link  Europe/Istanbul  Asia/Istanbul
338
339       The TARGET field should appear as the NAME field  in  some  zone  line.
340       The  LINK-NAME  field  is used as an alternative name for that zone; it
341       has the same syntax as a zone line's NAME field.
342
343       Except for continuation lines, lines may appear in any order in the in‐
344       put.   However,  the  behavior  is unspecified if multiple zone or link
345       lines define the same name, or if the source of one link  line  is  the
346       target of another.
347
348       The file that describes leap seconds can have leap lines and an expira‐
349       tion line.  Leap lines have the following form:
350
351            Leap  YEAR  MONTH  DAY  HH:MM:SS  CORR  R/S
352
353       For example:
354
355            Leap  2016  Dec    31   23:59:60  +     S
356
357       The YEAR, MONTH, DAY, and HH:MM:SS fields tell  when  the  leap  second
358       happened.  The CORR field should be “+” if a second was added or “-” if
359       a second was skipped.  The R/S field should  be  (an  abbreviation  of)
360       “Stationary”  if  the leap second time given by the other fields should
361       be interpreted as UTC or (an abbreviation of)  “Rolling”  if  the  leap
362       second  time  given  by the other fields should be interpreted as local
363       (wall clock) time.
364
365       The expiration line, if present, has the form:
366
367            Expires  YEAR  MONTH  DAY  HH:MM:SS
368
369       For example:
370
371            Expires  2020  Dec    28   00:00:00
372
373       The YEAR, MONTH, DAY, and HH:MM:SS fields give the expiration timestamp
374       in UTC for the leap second table; zic outputs this expiration timestamp
375       by truncating the end of the output file to the timestamp.  If there is
376       no expiration line, zic also accepts a comment “#expires E ...” where E
377       is the expiration timestamp as a decimal integer count of seconds since
378       the  Epoch, not counting leap seconds.  However, the “#expires” comment
379       is an obsolescent feature, and the leap second file should use an expi‐
380       ration line instead of relying on a comment.
381

EXTENDED EXAMPLE

383       Here  is  an extended example of zic input, intended to illustrate many
384       of its features.  In this example, the EU rules are  for  the  European
385       Union and for its predecessor organization, the European Communities.
386
387         # Rule  NAME  FROM  TO    TYPE  IN   ON       AT    SAVE  LETTER/S
388         Rule    Swiss 1941  1942  -     May  Mon>=1   1:00  1:00  S
389         Rule    Swiss 1941  1942  -     Oct  Mon>=1   2:00  0     -
390         Rule    EU    1977  1980  -     Apr  Sun>=1   1:00u 1:00  S
391         Rule    EU    1977  only  -     Sep  lastSun  1:00u 0     -
392         Rule    EU    1978  only  -     Oct   1       1:00u 0     -
393         Rule    EU    1979  1995  -     Sep  lastSun  1:00u 0     -
394         Rule    EU    1981  max   -     Mar  lastSun  1:00u 1:00  S
395         Rule    EU    1996  max   -     Oct  lastSun  1:00u 0     -
396
397         # Zone  NAME           STDOFF      RULES  FORMAT  [UNTIL]
398         Zone    Europe/Zurich  0:34:08     -      LMT     1853 Jul 16
399                                0:29:45.50  -      BMT     1894 Jun
400                                1:00        Swiss  CE%sT   1981
401                                1:00        EU     CE%sT
402
403         Link    Europe/Zurich  Europe/Vaduz
404
405       In  this  example,  the  timezone  is named Europe/Zurich but it has an
406       alias as Europe/Vaduz.  This example says that Zurich  was  34  minutes
407       and 8 seconds east of UT until 1853-07-16 at 00:00, when the legal off‐
408       set was changed to 7°26′22.50″, which  works  out  to  0:29:45.50;  zic
409       treats  this  by rounding it to 0:29:46.  After 1894-06-01 at 00:00 the
410       UT offset became one hour and Swiss daylight saving rules (defined with
411       lines beginning with “Rule Swiss”) apply.  From 1981 to the present, EU
412       daylight saving rules have applied, and the UTC offset has remained  at
413       one hour.
414
415       In 1941 and 1942, daylight saving time applied from the first Monday in
416       May at 01:00 to the first Monday in October at 02:00.  The pre-1981  EU
417       daylight-saving  rules  have  no effect here, but are included for com‐
418       pleteness.  Since 1981, daylight saving has begun on the last Sunday in
419       March  at  01:00 UTC.  Until 1995 it ended the last Sunday in September
420       at 01:00 UTC, but this changed to the last Sunday in  October  starting
421       in 1996.
422
423       For  purposes  of display, “LMT” and “BMT” were initially used, respec‐
424       tively.  Since Swiss rules and later EU rules were  applied,  the  time
425       zone  abbreviation has been CET for standard time and CEST for daylight
426       saving time.
427

FILES

429       /etc/localtime
430              Default local timezone file.
431
432       /usr/share/zoneinfo
433              Default timezone information directory.
434

NOTES

436       For areas with more than two types of local time, you may need  to  use
437       local  standard  time in the AT field of the earliest transition time's
438       rule to ensure that the earliest transition time recorded in  the  com‐
439       piled file is correct.
440
441       If,  for  a particular timezone, a clock advance caused by the start of
442       daylight saving coincides with and is equal to a clock  retreat  caused
443       by  a change in UT offset, zic produces a single transition to daylight
444       saving at the new UT offset without any change in  local  (wall  clock)
445       time.  To get separate transitions use multiple zone continuation lines
446       specifying transition instants using universal time.
447

SEE ALSO

449       tzfile(5), zdump(8)
450

COLOPHON

452       This page is part of release 5.10 of the Linux  man-pages  project.   A
453       description  of  the project, information about reporting bugs, and the
454       latest    version    of    this    page,    can     be     found     at
455       https://www.kernel.org/doc/man-pages/.
456
457
458
459                                  2020-08-13                            ZIC(8)
Impressum