1ZIC(8) Linux System Administration ZIC(8)
2
6 zic - timezone compiler
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9 zic [ option ... ] [ filename ... ]
10
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
14 input. If a filename is “-”, standard input is read.
15
17 --version
18 Output version information and exit.
19 --help Output short usage message and exit.
21 -d directory
23 Create time conversion information files in the named directory
24 rather than in the standard directory named below.
25 -l timezone
27 Use timezone as local time. zic will act as if the input con‐
28 tained a link line of the form
29 Link timezone localtime
31 -p timezone
33 Use timezone's rules when handling POSIX-format timezone envi‐
34 ronment variables. zic will act as if the input contained a
35 link line of the form
36 Link timezone posixrules
38 -L leapsecondfilename
40 Read leap second information from the file with the given name.
41 If this option is not used, no leap second information appears
42 in output files.
43 -v Be more verbose, and complain about the following situations:
45 The input specifies a link to a link.
47 A year that appears in a data file is outside the range of years
49 representable by time(2) values.
50 A time of 24:00 or more appears in the input. Pre-1998 versions
52 of zic prohibit 24:00, and pre-2007 versions prohibit times
53 greater than 24:00.
54 A rule goes past the start or end of the month. Pre-2004 ver‐
56 sions of zic prohibit this.
57 The output file does not contain all the information about the
59 long-term future of a timezone, because the future cannot be
60 summarized as an extended POSIX TZ string. For example, as of
61 2013 this problem occurs for Iran's daylight-saving rules for
62 the predicted future, as these rules are based on the Iranian
63 calendar, which cannot be represented.
64 The output contains data that may not be handled properly by
66 client code designed for older zic output formats. These com‐
67 patibility issues affect only timestamps before 1970 or after
68 the start of 2038.
69 A time zone abbreviation has fewer than 3 characters. POSIX
71 requires at least 3.
72 An output file name contains a byte that is not an ASCII letter,
74 “-”, “/”, or “_”; or it contains a file name component that con‐
75 tains more than 14 bytes or that starts with “-”.
76 -s Limit time values stored in output files to values that are the
78 same whether they're taken to be signed or unsigned. You can
79 use this option to generate SVVS-compatible files.
80 Input files should be text files, that is, they should be a series of
82 zero or more lines, each ending in a newline byte and containing at
83 most 511 bytes, and without any NUL bytes. The input text's encoding
84 is typically UTF-8 or ASCII; it should have a unibyte representation
85 for the POSIX Portable Character Set (PPCS) ⟨http://pubs.opengroup.org/
86 onlinepubs/9699919799/basedefs/V1_chap06.html⟩ and the encoding's non-
87 unibyte characters should consist entirely of non-PPCS bytes. Non-PPCS
88 characters typically occur only in comments: although output file names
89 and time zone abbreviations can contain nearly any character, other
90 software will work better if these are limited to the restricted syntax
91 described under the -v option.
92 Input lines are made up of fields. Fields are separated from one
94 another by one or more white space characters. The white space charac‐
95 ters are space, form feed, carriage return, newline, tab, and vertical
96 tab. Leading and trailing white space on input lines is ignored. An
97 unquoted sharp character (#) in the input introduces a comment which
98 extends to the end of the line the sharp character appears on. White
99 space characters and sharp characters may be enclosed in double quotes
100 (") if they're to be used as part of a field. Any line that is blank
101 (after comment stripping) is ignored. Nonblank lines are expected to
102 be of one of three types: rule lines, zone lines, and link lines.
103 Names must be in English and are case insensitive. They appear in sev‐
105 eral contexts, and include month and weekday names and keywords such as
106 maximum, only, Rolling, and Zone. A name can be abbreviated by omit‐
107 ting all but an initial prefix; any abbreviation must be unambiguous in
108 context.
109 A rule line has the form
111 Rule NAME FROM TO TYPE IN ON AT SAVE LETTER/S
113 For example:
115 Rule US 1967 1973 - Apr lastSun 2:00w 1:00 D
117 The fields that make up a rule line are:
119 NAME Gives the name of the rule set that contains this line. The
121 name must start with a character that is neither an ASCII digit
122 nor “-” nor “+”. To allow for future extensions, an unquoted
123 name should not contain characters from the set
124 “!$%&'()*,/:;<=>?@[\]^`{|}~”.
125 FROM Gives the first year in which the rule applies. Any signed
127 integer year can be supplied; the proleptic Gregorian calendar
128 is assumed, with year 0 preceding year 1. The word minimum (or
129 an abbreviation) means the indefinite past. The word maximum
130 (or an abbreviation) means the indefinite future. Rules can
131 describe times that are not representable as time values, with
132 the unrepresentable times ignored; this allows rules to be por‐
133 table among hosts with differing time value types.
134 TO Gives the final year in which the rule applies. In addition to
136 minimum and maximum (as above), the word only (or an abbrevia‐
137 tion) may be used to repeat the value of the FROM field.
138 TYPE should be “-” and is present for compatibility with older ver‐
140 sions of zic in which it could contain year types.
141 IN Names the month in which the rule takes effect. Month names
143 may be abbreviated.
144 ON Gives the day on which the rule takes effect. Recognized forms
146 include:
147 5 the fifth of the month
149 lastSun the last Sunday in the month
150 lastMon the last Monday in the month
151 Sun>=8 first Sunday on or after the eighth
152 Sun<=25 last Sunday on or before the 25th
153 A weekday name (e.g., Sunday) or a weekday name preceded by
155 “last” (e.g., lastSunday) may be abbreviated or spelled out in
156 full. Note that there must be no spaces within the ON field.
157 AT Gives the time of day at which the rule takes effect. Recog‐
159 nized forms include:
160 2 time in hours
162 2:00 time in hours and minutes
163 01:28:14 time in hours, minutes, and seconds
164 15:00 24-hour format time (for times after noon)
165 260:00 260 hours after 00:00
166 -2:30 2.5 hours before 00:00
167 - equivalent to 0
168 where hour 0 is midnight at the start of the day, and hour 24
170 is midnight at the end of the day. Any of these forms may be
171 followed by the letter w if the given time is local “wall
172 clock” time, s if the given time is local “standard” time, or u
173 (or g or z) if the given time is universal time; in the absence
174 of an indicator, wall clock time is assumed. The intent is
175 that a rule line describes the instants when a clock/calendar
176 set to the type of time specified in the AT field would show
177 the specified date and time of day.
178 SAVE Gives the amount of time to be added to local standard time
180 when the rule is in effect. This field has the same format as
181 the AT field (although, of course, the w and s suffixes are not
182 used). Negative offsets are allowed; in Ireland, for example,
183 daylight saving time is observed in winter and has a negative
184 offset relative to Irish Standard Time. The offset is merely
185 added to standard time; for example, zic does not distinguish a
186 10:30 standard time plus an 0:30 SAVE from a 10:00 standard
187 time plus a 1:00 SAVE.
188 LETTER/S
190 Gives the “variable part” (for example, the “S” or “D” in “EST”
191 or “EDT”) of time zone abbreviations to be used when this rule
192 is in effect. If this field is “-”, the variable part is null.
193 A zone line has the form
195 Zone NAME UTOFF RULES FORMAT [UNTIL]
197 For example:
199 Zone Asia/Amman 2:00 Jordan EE%sT 2017 Oct 27 01:00
201 The fields that make up a zone line are:
203 NAME The name of the timezone. This is the name used in creating the
205 time conversion information file for the timezone. It should not
206 contain a file name component “.” or “..”; a file name component
207 is a maximal substring that does not contain “/”.
208 UTOFF
210 The amount of time to add to UT to get standard time. This field
211 has the same format as the AT and SAVE fields of rule lines; begin
212 the field with a minus sign if time must be subtracted from UT.
213 RULES
215 The name of the rules that apply in the timezone or, alterna‐
216 tively, a field in the same format as a rule-line SAVE column,
217 giving of the amount of time to be added to local standard time
218 effect, and whether the resulting time is standard or daylight
219 saving. If this field is - then standard time always applies.
220 When an amount of time is given, only the sum of standard time and
221 this amount matters.
222 FORMAT
224 The format for time zone abbreviations. The pair of characters %s
225 is used to show where the “variable part” of the time zone abbre‐
226 viation goes. Alternatively, a format can use the pair of charac‐
227 ters %z to stand for the UT offset in the form ±hh, ±hhmm, or
228 ±hhmmss, using the shortest form that does not lose information,
229 where hh, mm, and ss are the hours, minutes, and seconds east (+)
230 or west (−) of UT. Alternatively, a slash (/) separates standard
231 and daylight abbreviations. To conform to POSIX, a time zone
232 abbreviation should contain only alphanumeric ASCII characters,
233 “+” and “-”.
234 UNTIL
236 The time at which the UT offset or the rule(s) change for a loca‐
237 tion. It takes the form of YEAR [MONTH [DAY [TIME]]]. If this is
238 specified, the time zone information is generated from the given
239 UT offset and rule change until the time specified, which is
240 interpreted using the rules in effect just before the transition.
241 The month, day, and time of day have the same format as the IN,
242 ON, and AT fields of a rule; trailing fields can be omitted, and
243 default to the earliest possible value for the missing fields.
244 The next line must be a “continuation” line; this has the same
246 form as a zone line except that the string “Zone” and the name are
247 omitted, as the continuation line will place information starting
248 at the time specified as the “until” information in the previous
249 line in the file used by the previous line. Continuation lines
250 may contain “until” information, just as zone lines do, indicating
251 that the next line is a further continuation.
252 If a zone changes at the same instant that a rule would otherwise take
254 effect in the earlier zone or continuation line, the rule is ignored.
255 In a single zone it is an error if two rules take effect at the same
256 instant, or if two zone changes take effect at the same instant.
257 A link line has the form
259 Link TARGET LINK-NAME
261 For example:
263 Link Europe/Istanbul Asia/Istanbul
265 The TARGET field should appear as the NAME field in some zone line.
267 The LINK-NAME field is used as an alternative name for that zone; it
268 has the same syntax as a zone line's NAME field.
269 Except for continuation lines, lines may appear in any order in the
271 input. However, the behavior is unspecified if multiple zone or link
272 lines define the same name, or if the source of one link line is the
273 target of another.
274 Lines in the file that describes leap seconds have the following form:
276 Leap YEAR MONTH DAY HH:MM:SS CORR R/S
278 For example:
280 Leap 2016 Dec 31 23:59:60 + S
282 The YEAR, MONTH, DAY, and HH:MM:SS fields tell when the leap second
284 happened. The CORR field should be “+” if a second was added or “-” if
285 a second was skipped. The R/S field should be (an abbreviation of)
286 “Stationary” if the leap second time given by the other fields should
287 be interpreted as UTC or (an abbreviation of) “Rolling” if the leap
288 second time given by the other fields should be interpreted as local
289 wall clock time.
290
292 Here is an extended example of zic input, intended to illustrate many
293 of its features. In this example, the EU rules are for the European
294 Union and for its predecessor organization, the European Communities.
295 # Rule NAME FROM TO TYPE IN ON AT SAVE LETTER/S
297 Rule Swiss 1941 1942 - May Mon>=1 1:00 1:00 S
298 Rule Swiss 1941 1942 - Oct Mon>=1 2:00 0 -
299 Rule EU 1977 1980 - Apr Sun>=1 1:00u 1:00 S
300 Rule EU 1977 only - Sep lastSun 1:00u 0 -
301 Rule EU 1978 only - Oct 1 1:00u 0 -
302 Rule EU 1979 1995 - Sep lastSun 1:00u 0 -
303 Rule EU 1981 max - Mar lastSun 1:00u 1:00 S
304 Rule EU 1996 max - Oct lastSun 1:00u 0 -
305 # Zone NAME UTOFF RULES FORMAT [UNTIL]
307 Zone Europe/Zurich 0:34:08 - LMT 1853 Jul 16
308 0:29:46 - BMT 1894 Jun
309 1:00 Swiss CE%sT 1981
310 1:00 EU CE%sT
311 Link Europe/Zurich Europe/Vaduz
313 In this example, the timezone is named Europe/Zurich but it has an
315 alias as Europe/Vaduz. This example says that Zurich was 34 minutes
316 and 8 seconds east of UT until 1853-07-16 at 00:00, when the legal off‐
317 set was changed to 7°26′22.50″; although this works out to 0:29:45.50,
318 the input format cannot represent fractional seconds so it is rounded
319 here. After 1894-06-01 at 00:00 the UT offset became one hour and
320 Swiss daylight saving rules (defined with lines beginning with “Rule
321 Swiss”) apply. From 1981 to the present, EU daylight saving rules have
322 applied, and the UTC offset has remained at one hour.
323 In 1941 and 1942, daylight saving time applied from the first Monday in
325 May at 01:00 to the first Monday in October at 02:00. The pre-1981 EU
326 daylight-saving rules have no effect here, but are included for com‐
327 pleteness. Since 1981, daylight saving has begun on the last Sunday in
328 March at 01:00 UTC. Until 1995 it ended the last Sunday in September
329 at 01:00 UTC, but this changed to the last Sunday in October starting
330 in 1996.
331 For purposes of display, “LMT” and “BMT” were initially used, respec‐
333 tively. Since Swiss rules and later EU rules were applied, the time
334 zone abbreviation has been CET for standard time and CEST for daylight
335 saving time.
336
338 /etc/localtime
339 Default local timezone file.
340 /usr/share/zoneinfo
342 Default timezone information directory.
343
345 For areas with more than two types of local time, you may need to use
346 local standard time in the AT field of the earliest transition time's
347 rule to ensure that the earliest transition time recorded in the com‐
348 piled file is correct.
349 If, for a particular timezone, a clock advance caused by the start of
351 daylight saving coincides with and is equal to a clock retreat caused
352 by a change in UT offset, zic produces a single transition to daylight
353 saving at the new UT offset (without any change in wall clock time).
354 To get separate transitions use multiple zone continuation lines speci‐
355 fying transition instants using universal time.
356
358 tzfile(5), zdump(8)
359
361 This page is part of release 5.07 of the Linux man-pages project. A
362 description of the project, information about reporting bugs, and the
363 latest version of this page, can be found at
364 https://www.kernel.org/doc/man-pages/.
365 2019-03-06 ZIC(8)