1zic(8) System Manager's Manual zic(8) 2 3NAME 4 zic - timezone compiler 5 6SYNOPSIS 7 zic [ option ... ] [ filename ... ] 8 9DESCRIPTION 10 The zic program reads text from the file(s) named on the command line 11 and creates the timezone information format (TZif) files specified in 12 this input. If a filename is "-", standard input is read. 13 14OPTIONS 15 --version 16 Output version information and exit. 17 18 --help Output short usage message and exit. 19 20 -b bloat 21 Output backward-compatibility data as specified by bloat. If 22 bloat is fat, generate additional data entries that work around 23 potential bugs or incompatibilities in older software, such as 24 software that mishandles the 64-bit generated data. If bloat is 25 slim, keep the output files small; this can help check for the 26 bugs and incompatibilities. The default is slim, as software 27 that mishandles 64-bit data typically mishandles timestamps 28 after the year 2038 anyway. Also see the -r option for another 29 way to alter output size. 30 31 -d directory 32 Create time conversion information files in the named directory 33 rather than in the standard directory named below. 34 35 -l timezone 36 Use timezone as local time. zic will act as if the input 37 contained a link line of the form 38 39 Link timezone localtime 40 41 If timezone is -, any already-existing link is removed. 42 43 -L leapsecondfilename 44 Read leap second information from the file with the given name. 45 If this option is not used, no leap second information appears 46 in output files. 47 48 -p timezone 49 Use timezone's rules when handling nonstandard TZ strings like 50 "EET-2EEST" that lack transition rules. zic will act as if the 51 input contained a link line of the form 52 53 Link timezone posixrules 54 55 If timezone is "-" (the default), any already-existing link is 56 removed. 57 58 Unless timezone is "-", this option is obsolete and poorly 59 supported. Among other things it should not be used for 60 timestamps after the year 2037, and it should not be combined 61 with -b slim if timezone's transitions are at standard time or 62 Universal Time (UT) instead of local time. 63 64 -r [@lo][/@hi] 65 Limit the applicability of output files to timestamps in the 66 range from lo (inclusive) to hi (exclusive), where lo and hi are 67 possibly signed decimal counts of seconds since the Epoch 68 (1970-01-01 00:00:00 UTC). Omitted counts default to extreme 69 values. The output files use UT offset 0 and abbreviation "-00" 70 in place of the omitted timestamp data. For example, "zic -r 71 @0" omits data intended for negative timestamps (i.e., before 72 the Epoch), and "zic -r @0/@2147483648" outputs data intended 73 only for nonnegative timestamps that fit into 31-bit signed 74 integers. On platforms with GNU date, "zic -r @$(date +%s)" 75 omits data intended for past timestamps. Although this option 76 typically reduces the output file's size, the size can increase 77 due to the need to represent the timestamp range boundaries, 78 particularly if hi causes a TZif file to contain explicit 79 entries for pre-hi transitions rather than concisely 80 representing them with an extended POSIX.1-2017 TZ string. Also 81 see the -b slim option for another way to shrink output size. 82 83 -R @hi Generate redundant trailing explicit transitions for timestamps 84 that occur less than hi seconds since the Epoch, even though the 85 transitions could be more concisely represented via the extended 86 POSIX.1-2017 TZ string. This option does not affect the 87 represented timestamps. Although it accommodates nonstandard 88 TZif readers that ignore the extended POSIX.1-2017 TZ string, it 89 increases the size of the altered output files. 90 91 -t file 92 When creating local time information, put the configuration link 93 in the named file rather than in the standard location. 94 95 -v Be more verbose, and complain about the following situations: 96 97 The input specifies a link to a link, something not supported by 98 some older parsers, including zic itself through release 2022e. 99 100 A year that appears in a data file is outside the range of 101 representable years. 102 103 A time of 24:00 or more appears in the input. Pre-1998 versions 104 of zic prohibit 24:00, and pre-2007 versions prohibit times 105 greater than 24:00. 106 107 A rule goes past the start or end of the month. Pre-2004 108 versions of zic prohibit this. 109 110 A time zone abbreviation uses a %z format. Pre-2015 versions of 111 zic do not support this. 112 113 A timestamp contains fractional seconds. Pre-2018 versions of 114 zic do not support this. 115 116 The input contains abbreviations that are mishandled by pre-2018 117 versions of zic due to a longstanding coding bug. These 118 abbreviations include "L" for "Link", "mi" for "min", "Sa" for 119 "Sat", and "Su" for "Sun". 120 121 The output file does not contain all the information about the 122 long-term future of a timezone, because the future cannot be 123 summarized as an extended POSIX.1-2017 TZ string. For example, 124 as of 2023 this problem occurs for Morocco's daylight-saving 125 rules, as these rules are based on predictions for when Ramadan 126 will be observed, something that an extended POSIX.1-2017 TZ 127 string cannot represent. 128 129 The output contains data that may not be handled properly by 130 client code designed for older zic output formats. These 131 compatibility issues affect only timestamps before 1970 or after 132 the start of 2038. 133 134 The output contains a truncated leap second table, which can 135 cause some older TZif readers to misbehave. This can occur if 136 the -L option is used, and either an Expires line is present or 137 the -r option is also used. 138 139 The output file contains more than 1200 transitions, which may 140 be mishandled by some clients. The current reference client 141 supports at most 2000 transitions; pre-2014 versions of the 142 reference client support at most 1200 transitions. 143 144 A time zone abbreviation has fewer than 3 or more than 6 145 characters. POSIX requires at least 3, and requires 146 implementations to support at least 6. 147 148 An output file name contains a byte that is not an ASCII letter, 149 "-", "/", or "_"; or it contains a file name component that 150 contains more than 14 bytes or that starts with "-". 151 152FILES 153 Input files use the format described in this section; output files use 154 tzfile(5) format. 155 156 Input files should be text files, that is, they should be a series of 157 zero or more lines, each ending in a newline byte and containing at 158 most 2048 bytes counting the newline, and without any NUL bytes. The 159 input text's encoding is typically UTF-8 or ASCII; it should have a 160 unibyte representation for the POSIX Portable Character Set (PPCS) 161 <https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap06 162 .html> and the encoding's non-unibyte characters should consist 163 entirely of non-PPCS bytes. Non-PPCS characters typically occur only 164 in comments: although output file names and time zone abbreviations can 165 contain nearly any character, other software will work better if these 166 are limited to the restricted syntax described under the -v option. 167 168 Input lines are made up of fields. Fields are separated from one 169 another by one or more white space characters. The white space 170 characters are space, form feed, carriage return, newline, tab, and 171 vertical tab. Leading and trailing white space on input lines is 172 ignored. An unquoted sharp character (#) in the input introduces a 173 comment which extends to the end of the line the sharp character 174 appears on. White space characters and sharp characters may be 175 enclosed in double quotes (") if they're to be used as part of a field. 176 Any line that is blank (after comment stripping) is ignored. Nonblank 177 lines are expected to be of one of three types: rule lines, zone lines, 178 and link lines. 179 180 Names must be in English and are case insensitive. They appear in 181 several contexts, and include month and weekday names and keywords such 182 as maximum, only, Rolling, and Zone. A name can be abbreviated by 183 omitting all but an initial prefix; any abbreviation must be 184 unambiguous in context. 185 186 A rule line has the form 187 188 Rule NAME FROM TO - IN ON AT SAVE LETTER/S 189 190 For example: 191 192 Rule US 1967 1973 - Apr lastSun 2:00w 1:00d D 193 194 The fields that make up a rule line are: 195 196 NAME Gives the name of the rule set that contains this line. The 197 name must start with a character that is neither an ASCII digit 198 nor "-" nor "+". To allow for future extensions, an unquoted 199 name should not contain characters from the set 200 "!$%&'()*,/:;<=>?@[\]^`{|}~". 201 202 FROM Gives the first year in which the rule applies. Any signed 203 integer year can be supplied; the proleptic Gregorian calendar 204 is assumed, with year 0 preceding year 1. Rules can describe 205 times that are not representable as time values, with the 206 unrepresentable times ignored; this allows rules to be portable 207 among hosts with differing time value types. 208 209 TO Gives the final year in which the rule applies. The word 210 maximum (or an abbreviation) means the indefinite future, and 211 the word only (or an abbreviation) may be used to repeat the 212 value of the FROM field. 213 214 - Is a reserved field and should always contain "-" for 215 compatibility with older versions of zic. It was previously 216 known as the TYPE field, which could contain values to allow a 217 separate script to further restrict in which "types" of years 218 the rule would apply. 219 220 IN Names the month in which the rule takes effect. Month names may 221 be abbreviated. 222 223 ON Gives the day on which the rule takes effect. Recognized forms 224 include: 225 226 5 the fifth of the month 227 lastSun the last Sunday in the month 228 lastMon the last Monday in the month 229 Sun>=8 first Sunday on or after the eighth 230 Sun<=25 last Sunday on or before the 25th 231 232 A weekday name (e.g., Sunday) or a weekday name preceded by 233 "last" (e.g., lastSunday) may be abbreviated or spelled out in 234 full. There must be no white space characters within the ON 235 field. The "<=" and ">=" constructs can result in a day in the 236 neighboring month; for example, the IN-ON combination "Oct 237 Sun>=31" stands for the first Sunday on or after October 31, 238 even if that Sunday occurs in November. 239 240 AT Gives the time of day at which the rule takes effect, relative 241 to 00:00, the start of a calendar day. Recognized forms 242 include: 243 244 2 time in hours 245 2:00 time in hours and minutes 246 01:28:14 time in hours, minutes, and seconds 247 00:19:32.13 time with fractional seconds 248 12:00 midday, 12 hours after 00:00 249 15:00 3 PM, 15 hours after 00:00 250 24:00 end of day, 24 hours after 00:00 251 260:00 260 hours after 00:00 252 -2:30 2.5 hours before 00:00 253 - equivalent to 0 254 255 Although zic rounds times to the nearest integer second 256 (breaking ties to the even integer), the fractions may be useful 257 to other applications requiring greater precision. The source 258 format does not specify any maximum precision. Any of these 259 forms may be followed by the letter w if the given time is local 260 or "wall clock" time, s if the given time is standard time 261 without any adjustment for daylight saving, or u (or g or z) if 262 the given time is universal time; in the absence of an 263 indicator, local (wall clock) time is assumed. These forms 264 ignore leap seconds; for example, if a leap second occurs at 265 00:59:60 local time, "1:00" stands for 3601 seconds after local 266 midnight instead of the usual 3600 seconds. The intent is that 267 a rule line describes the instants when a clock/calendar set to 268 the type of time specified in the AT field would show the 269 specified date and time of day. 270 271 SAVE Gives the amount of time to be added to local standard time when 272 the rule is in effect, and whether the resulting time is 273 standard or daylight saving. This field has the same format as 274 the AT field except with a different set of suffix letters: s 275 for standard time and d for daylight saving time. The suffix 276 letter is typically omitted, and defaults to s if the offset is 277 zero and to d otherwise. Negative offsets are allowed; in 278 Ireland, for example, daylight saving time is observed in winter 279 and has a negative offset relative to Irish Standard Time. The 280 offset is merely added to standard time; for example, zic does 281 not distinguish a 10:30 standard time plus an 0:30 SAVE from a 282 10:00 standard time plus a 1:00 SAVE. 283 284 LETTER/S 285 Gives the "variable part" (for example, the "S" or "D" in "EST" 286 or "EDT") of time zone abbreviations to be used when this rule 287 is in effect. If this field is "-", the variable part is null. 288 289 A zone line has the form 290 291 Zone NAME STDOFF RULES FORMAT [UNTIL] 292 293 For example: 294 295 Zone Asia/Amman 2:00 Jordan EE%sT 2017 Oct 27 01:00 296 297 The fields that make up a zone line are: 298 299 NAME The name of the timezone. This is the name used in creating the 300 time conversion information file for the timezone. It should 301 not contain a file name component "." or ".."; a file name 302 component is a maximal substring that does not contain "/". 303 304 STDOFF The amount of time to add to UT to get standard time, without 305 any adjustment for daylight saving. This field has the same 306 format as the AT and SAVE fields of rule lines, except without 307 suffix letters; begin the field with a minus sign if time must 308 be subtracted from UT. 309 310 RULES The name of the rules that apply in the timezone or, 311 alternatively, a field in the same format as a rule-line SAVE 312 column, giving the amount of time to be added to local standard 313 time and whether the resulting time is standard or daylight 314 saving. If this field is - then standard time always applies. 315 When an amount of time is given, only the sum of standard time 316 and this amount matters. 317 318 FORMAT The format for time zone abbreviations. The pair of characters 319 %s is used to show where the "variable part" of the time zone 320 abbreviation goes. Alternatively, a format can use the pair of 321 characters %z to stand for the UT offset in the form +-hh, 322 +-hhmm, or +-hhmmss, using the shortest form that does not lose 323 information, where hh, mm, and ss are the hours, minutes, and 324 seconds east (+) or west (-) of UT. Alternatively, a slash (/) 325 separates standard and daylight abbreviations. To conform to 326 POSIX, a time zone abbreviation should contain only alphanumeric 327 ASCII characters, "+" and "-". By convention, the time zone 328 abbreviation "-00" is a placeholder that means local time is 329 unspecified. 330 331 UNTIL The time at which the UT offset or the rule(s) change for a 332 location. It takes the form of one to four fields YEAR [MONTH 333 [DAY [TIME]]]. If this is specified, the time zone information 334 is generated from the given UT offset and rule change until the 335 time specified, which is interpreted using the rules in effect 336 just before the transition. The month, day, and time of day 337 have the same format as the IN, ON, and AT fields of a rule; 338 trailing fields can be omitted, and default to the earliest 339 possible value for the missing fields. 340 341 The next line must be a "continuation" line; this has the same 342 form as a zone line except that the string "Zone" and the name 343 are omitted, as the continuation line will place information 344 starting at the time specified as the "until" information in the 345 previous line in the file used by the previous line. 346 Continuation lines may contain "until" information, just as zone 347 lines do, indicating that the next line is a further 348 continuation. 349 350 If a zone changes at the same instant that a rule would otherwise take 351 effect in the earlier zone or continuation line, the rule is ignored. 352 A zone or continuation line L with a named rule set starts with 353 standard time by default: that is, any of L's timestamps preceding L's 354 earliest rule use the rule in effect after L's first transition into 355 standard time. In a single zone it is an error if two rules take 356 effect at the same instant, or if two zone changes take effect at the 357 same instant. 358 359 If a continuation line subtracts N seconds from the UT offset after a 360 transition that would be interpreted to be later if using the 361 continuation line's UT offset and rules, the "until" time of the 362 previous zone or continuation line is interpreted according to the 363 continuation line's UT offset and rules, and any rule that would 364 otherwise take effect in the next N seconds is instead assumed to take 365 effect simultaneously. For example: 366 367 # Rule NAME FROM TO - IN ON AT SAVE LETTER/S 368 Rule US 1967 2006 - Oct lastSun 2:00 0 S 369 Rule US 1967 1973 - Apr lastSun 2:00 1:00 D 370 # Zone NAME STDOFF RULES FORMAT [UNTIL] 371 Zone America/Menominee -5:00 - EST 1973 Apr 29 2:00 372 -6:00 US C%sT 373 374 Here, an incorrect reading would be there were two clock changes on 375 1973-04-29, the first from 02:00 EST (-05) to 01:00 CST (-06), and the 376 second an hour later from 02:00 CST (-06) to 03:00 CDT (-05). However, 377 zic interprets this more sensibly as a single transition from 02:00 CST 378 (-05) to 02:00 CDT (-05). 379 380 A link line has the form 381 382 Link TARGET LINK-NAME 383 384 For example: 385 386 Link Europe/Istanbul Asia/Istanbul 387 388 The TARGET field should appear as the NAME field in some zone line or 389 as the LINK-NAME field in some link line. The LINK-NAME field is used 390 as an alternative name for that zone; it has the same syntax as a zone 391 line's NAME field. Links can chain together, although the behavior is 392 unspecified if a chain of one or more links does not terminate in a 393 Zone name. A link line can appear before the line that defines the 394 link target. For example: 395 396 Link Greenwich G_M_T 397 Link Etc/GMT Greenwich 398 Zone Etc/GMT 0 - GMT 399 400 The two links are chained together, and G_M_T, Greenwich, and Etc/GMT 401 all name the same zone. 402 403 Except for continuation lines, lines may appear in any order in the 404 input. However, the behavior is unspecified if multiple zone or link 405 lines define the same name. 406 407 The file that describes leap seconds can have leap lines and an 408 expiration line. Leap lines have the following form: 409 410 Leap YEAR MONTH DAY HH:MM:SS CORR R/S 411 412 For example: 413 414 Leap 2016 Dec 31 23:59:60 + S 415 416 The YEAR, MONTH, DAY, and HH:MM:SS fields tell when the leap second 417 happened. The CORR field should be "+" if a second was added or "-" if 418 a second was skipped. The R/S field should be (an abbreviation of) 419 "Stationary" if the leap second time given by the other fields should 420 be interpreted as UTC or (an abbreviation of) "Rolling" if the leap 421 second time given by the other fields should be interpreted as local 422 (wall clock) time. 423 424 Rolling leap seconds were implemented back when it was not clear 425 whether common practice was rolling or stationary, with concerns that 426 one would see Times Square ball drops where there'd be a "3... 2... 427 1... leap... Happy New Year" countdown, placing the leap second at 428 midnight New York time rather than midnight UTC. However, this 429 countdown style does not seem to have caught on, which means rolling 430 leap seconds are not used in practice; also, they are not supported if 431 the -r option is used. 432 433 The expiration line, if present, has the form: 434 435 Expires YEAR MONTH DAY HH:MM:SS 436 437 For example: 438 439 Expires 2020 Dec 28 00:00:00 440 441 The YEAR, MONTH, DAY, and HH:MM:SS fields give the expiration timestamp 442 in UTC for the leap second table. 443 444EXTENDED EXAMPLE 445 Here is an extended example of zic input, intended to illustrate many 446 of its features. 447 448 # Rule NAME FROM TO - IN ON AT SAVE LETTER/S 449 Rule Swiss 1941 1942 - May Mon>=1 1:00 1:00 S 450 Rule Swiss 1941 1942 - Oct Mon>=1 2:00 0 - 451 Rule EU 1977 1980 - Apr Sun>=1 1:00u 1:00 S 452 Rule EU 1977 only - Sep lastSun 1:00u 0 - 453 Rule EU 1978 only - Oct 1 1:00u 0 - 454 Rule EU 1979 1995 - Sep lastSun 1:00u 0 - 455 Rule EU 1981 max - Mar lastSun 1:00u 1:00 S 456 Rule EU 1996 max - Oct lastSun 1:00u 0 - 457 458 # Zone NAME STDOFF RULES FORMAT [UNTIL] 459 Zone Europe/Zurich 0:34:08 - LMT 1853 Jul 16 460 0:29:45.50 - BMT 1894 Jun 461 1:00 Swiss CE%sT 1981 462 1:00 EU CE%sT 463 464 Link Europe/Zurich Europe/Vaduz 465 466 In this example, the EU rules are for the European Union and for its 467 predecessor organization, the European Communities. The timezone is 468 named Europe/Zurich and it has the alias Europe/Vaduz. This example 469 says that Zurich was 34 minutes and 8 seconds east of UT until 470 1853-07-16 at 00:00, when the legal offset was changed to 7 degrees 26 471 minutes 22.50 seconds, which works out to 0:29:45.50; zic treats this 472 by rounding it to 0:29:46. After 1894-06-01 at 00:00 the UT offset 473 became one hour and Swiss daylight saving rules (defined with lines 474 beginning with "Rule Swiss") apply. From 1981 to the present, EU 475 daylight saving rules have applied, and the UTC offset has remained at 476 one hour. 477 478 In 1941 and 1942, daylight saving time applied from the first Monday in 479 May at 01:00 to the first Monday in October at 02:00. The pre-1981 EU 480 daylight-saving rules have no effect here, but are included for 481 completeness. Since 1981, daylight saving has begun on the last Sunday 482 in March at 01:00 UTC. Until 1995 it ended the last Sunday in 483 September at 01:00 UTC, but this changed to the last Sunday in October 484 starting in 1996. 485 486 For purposes of display, "LMT" and "BMT" were initially used, 487 respectively. Since Swiss rules and later EU rules were applied, the 488 time zone abbreviation has been CET for standard time and CEST for 489 daylight saving time. 490 491FILES 492 /etc/localtime 493 Default local timezone file. 494 495 /usr/share/zoneinfo 496 Default timezone information directory. 497 498NOTES 499 For areas with more than two types of local time, you may need to use 500 local standard time in the AT field of the earliest transition time's 501 rule to ensure that the earliest transition time recorded in the 502 compiled file is correct. 503 504 If, for a particular timezone, a clock advance caused by the start of 505 daylight saving coincides with and is equal to a clock retreat caused 506 by a change in UT offset, zic produces a single transition to daylight 507 saving at the new UT offset without any change in local (wall clock) 508 time. To get separate transitions use multiple zone continuation lines 509 specifying transition instants using universal time. 510 511SEE ALSO 512 tzfile(5), zdump(8) 513 514Time Zone Database zic(8) 515