1.\" This file is in the public domain, so clarified as of 2.\" 2009-05-17 by Arthur David Olson. 3.Dd March 8, 2026 4.Dt ZIC 8 5.Os 6.Sh NAME 7.Nm zic 8.Nd timezone compiler 9.Sh SYNOPSIS 10.Nm 11.Op Fl -help 12.Op Fl -version 13.Op Fl Dsv 14.Op Fl b Ar slim | fat 15.Op Fl d Ar directory 16.Op Fl l Ar localtime 17.Op Fl L Ar leapseconds 18.Op Fl m Ar mode 19.Op Fl p Ar posixrules 20.Oo 21.Fl r 22.Op @ Ns Ar lo Ns 23.Op /@ Ns Ar hi 24.Oc 25.Op Fl R @ Ns Ar hi 26.Op Fl t Ar localtime-link 27.Op Fl u Ar owner Ns Op Li : Ns Ar group 28.Op Ar filename ... 29.Sh DESCRIPTION 30The 31.Nm 32program reads text from the file(s) named on the command line 33and creates the timezone information format (TZif) files 34specified in this input. 35If a 36.Ar filename 37is 38.Dq "-" , 39standard input is read. 40.Pp 41The following options are available: 42.Bl -tag -width indent 43.It Fl -version 44Output version information and exit. 45.It Fl -help 46Output short usage message and exit. 47.It Fl b Ar bloat 48Output backward-compatibility data as specified by 49.Ar bloat . 50If 51.Ar bloat 52is 53.Cm fat , 54generate additional data entries that work around potential bugs or 55incompatibilities in older software, such as software that mishandles 56a TZif file's 64-bit data or proleptic TZ string. 57If 58.Ar bloat 59is 60.Cm slim , 61keep the output files small; this can help check for the bugs 62and incompatibilities. 63The default is 64.Cm slim , 65as the 66.Cm fat 67workarounds are typically good only until the year 2038 anyway. 68Also see the 69.Fl r 70option for another way to alter output size. 71.It Fl D 72Do not create ancestor directories of output files, 73For example, for a zone named America/Los_Angeles 74the directory America should already exist. 75By default, the directory and its ancestors are created 76if they do not already exist. 77.It Fl d Ar directory 78Create time conversion information files in the named directory rather than 79in the standard directory named below. 80.It Fl l Ar timezone 81Use 82.Ar timezone 83as local time. 84The 85.Nm 86utility 87will act as if the input contained a link line of the form 88.Bd -literal -offset indent 89Link timezone localtime 90.Ed 91.Pp 92If 93.Ar timezone 94is 95.Ql - , 96any already-existing link is removed. 97.It Fl L Ar filename 98Read leap second information from the file with the given name. 99If this option is not used, 100no leap second information appears in output files; 101this is required by some TZif readers. 102.It Fl p Ar timezone 103Act as if the input contained a link line of the form 104.Bd -literal -offset indent 105Link \fItimezone\fP posixrules 106.Ed 107.Pp 108If 109.Ar timezone 110is 111.Dq "\-" 112(the default), any already-existing link is removed. 113.Pp 114Unless 115.Ar timezone 116is 117.Dq "\-" , 118this option is obsolete and is no longer supported by most runtimes. 119Among other things it should not be used for timestamps after the year 2037, 120and it should not be combined with 121.Fl b Cm slim 122if 123.Ar timezone 's 124transitions are at standard time or Universal Time (UT) instead of local time. 125The option is present only to support obsolete runtimes that used 126.Ar timezone 's 127rules when handling obsolescent 128TZ strings like "AST4ADT" that lack transition rules; 129modern runtimes that support these TZ strings 130typically just use current US rules 131as the TZ strings were mainly used in the US. 132Similarly, any Zone or Link named "posixrules" is obsolete and problematic. 133.It Fl m Ar mode 134Create TZif files with the given file mode bits. 135By default the files are created with mode 644 as modified by the umask. 136With this option they are created with the given mode instead. 137For portability the mode should be an unsigned octal integer, 138typically 644 or 444; 139some platforms also support 140.Xr chmod 1 -style 141symbolic modes. 142This option does not affect created ancestor directories, 143which have mode 755 as modified by the umask. 144The option is ignored on platforms lacking the notion of file mode bits. 145.It Fl r Oo @ Ns Ar lo Oc Ns Oo /@ Ns Ar hi Oc 146Limit the applicability of output files 147to timestamps in the range from 148.Ar lo 149(inclusive) to 150.Ar hi 151(exclusive), where 152.Ar lo 153and 154.Ar hi 155are possibly signed decimal counts of seconds since the Epoch 156(1970-01-01 00:00:00 UTC). 157Omitted counts default to extreme values. 158The output files use UT offset 0 and abbreviation 159.Dq "\-00" 160in place of the omitted timestamp data. 161For example, 162.Fl r @0 163omits data intended for negative timestamps (i.e., before the Epoch), and 164.Fl r @0/@2147483648 165outputs data intended only for nonnegative timestamps that fit into 16631-bit signed integers. 167On platforms with GNU 168.Nm date , 169.Dq "zic \-r @$(date +%s)" 170omits data intended for past timestamps. 171Although this option typically reduces the output file's size, 172the size can increase due to the need to represent the timestamp range 173boundaries, particularly if 174.Ar hi 175causes a TZif file to contain explicit entries for 176.Em pre- 177.Ar hi 178transitions rather than concisely representing them 179with a proleptic TZ string. 180Also see the 181.Fl b Cm slim 182option for another way to shrink output size. 183.It Fl R @ Ns Ar hi 184Generate redundant trailing explicit transitions for timestamps 185that occur less than 186.Ar hi 187seconds since the Epoch, even though the transitions could be 188more concisely represented via the proleptic TZ string. 189This option does not affect the represented timestamps. 190Although it accommodates nonstandard TZif readers 191that ignore the proleptic TZ string, 192it increases the size of the altered output files. 193.It Fl t Ar file 194When creating local time information, put the configuration link in 195the named file rather than in the standard location. 196.It Fl u Ar owner Ns Op Li : Ns Ar group 197Change the output regular files' owner and group to those specified. 198The 199.Ar owner 200is either a user name, or an unsigned decimal integer user ID, 201or an empty string meaning no change to the owner. 202The 203.Ar group 204is similar for group names and IDs. 205This option does not affect directories or hard or symbolic links. 206It typically needs special privileges to change ownership, 207and is ignored on platforms that lack the notions of owners and groups. 208.It Fl v 209Be more verbose, and complain about the following situations: 210.Bl -bullet 211.It 212The input specifies a link to a link, 213something not supported by some older parsers, including 214.Nm 215itself through release 2022e. 216.It 217A year that appears in a data file is outside the range 218of representable years. 219.It 220A time of 24:00 or more appears in the input. 221Pre-1998 versions of 222.Nm 223prohibit 24:00, and pre-2007 versions prohibit times greater than 24:00. 224.It 225A rule goes past the start or end of the month. 226Pre-2004 versions of 227.Nm 228prohibit this. 229.It 230A time zone abbreviation uses a 231.Ql %z 232format. 233Pre-2015 versions of 234.Nm 235do not support this. 236.It 237A timestamp contains fractional seconds. 238Pre-2018 versions of 239.Nm 240do not support this. 241.It 242The input contains abbreviations that are mishandled by pre-2018 versions of 243.Nm 244due to a longstanding coding bug. 245These abbreviations include 246.Dq L 247for 248.Dq Link , 249.Dq mi 250for 251.Dq min , 252.Dq Sa 253for 254.Dq Sat , 255and 256.Dq Su 257for 258.Dq Sun . 259.It 260The output file does not contain all the information about the 261long-term future of a timezone, because the future cannot be summarized as 262a proleptic TZ string. For example, as of 2023 this problem 263occurs for Morocco's daylight-saving rules, as these rules are based 264on predictions for when Ramadan will be observed, something that 265a proleptic TZ string cannot represent. 266.It 267The output contains data that may not be handled properly by client 268code designed for older 269.Nm 270output formats. 271These compatibility issues affect only timestamps 272before 1970 or after the start of 2038. 273.It 274The output contains a truncated leap second table, 275which can cause some older TZif readers to misbehave. 276This can occur if the 277.Fl L 278option is used, and either an Expires line is present or 279the 280.Fl r 281option is also used. 282.It 283The output file contains more than 1200 transitions, 284which may be mishandled by some clients. 285The current reference client supports at most 2000 transitions; 286pre-2014 versions of the reference client support at most 1200 287transitions. 288.It 289A time zone abbreviation has fewer than 3 or more than 6 characters. 290POSIX requires at least 3, and requires implementations to support 291at least 6. 292.It 293An output file name contains a byte that is not an ASCII letter, 294.Dq "\-" , 295.Dq "/" , 296or 297.Dq "_" ; 298or it contains a file name component that contains more than 14 bytes 299or that starts with 300.Dq "\-" . 301.El 302.El 303.RE 304.Sh FILES 305Input files use the format described in this section; output files use 306.Xr tzfile 5 307format. 308.Pp 309Input files should be text files, that is, they should be a series of 310zero or more lines, each ending in a newline byte and containing at 311most 2048 bytes counting the newline, and without any NUL bytes. 312The input text's encoding 313is typically UTF-8 or ASCII; it should have a unibyte representation 314for the 315.UR https://\:pubs\:.opengroup\:.org/\:onlinepubs/\:9799919799/\:basedefs/\:V1_chap06\:.html 316POSIX Portable Character Set (PPCS) 317.UE 318and the encoding's non-unibyte characters should consist entirely of 319non-PPCS bytes. 320Non-PPCS characters typically occur only in comments: 321although output file names and time zone abbreviations can contain 322nearly any character, other software will work better if these are 323limited to the restricted syntax described under the 324.Fl v 325option. 326.Pp 327Input lines are made up of fields. 328Fields are separated from one another by one or more white space characters. 329The white space characters are space, form feed, carriage return, newline, 330tab, and vertical tab. 331Leading and trailing white space on input lines is ignored. 332An unquoted sharp character (\(sh) in the input introduces a comment which extends 333to the end of the line the sharp character appears on. 334White space characters and sharp characters may be enclosed in double quotes 335(\(dq) if they're to be used as part of a field. 336Any line that is blank (after comment stripping) is ignored. 337Nonblank lines are expected to be of one of three types: 338rule lines, zone lines, and link lines. 339.Pp 340Names must be in English and are case insensitive. 341They appear in several contexts, and include month and weekday names 342and keywords such as 343.Dq "maximum" , 344.Dq "only" , 345.Dq "Rolling" , 346and 347.Dq "Zone" . 348A name can be abbreviated by omitting all but an initial prefix; any 349abbreviation must be unambiguous in context. 350.Pp 351A rule line has the form 352.Bd -literal 353Rule NAME FROM TO \- IN ON AT SAVE LETTER/S 354.Ed 355.Pp 356For example: 357.Bd -literal 358Rule US 1967 1973 \- Apr lastSun 2:00w 1:00d D 359.Ed 360.Pp 361The fields that make up a rule line are: 362.Bl -tag -width "LETTER/S" 363.It NAME 364Gives the name of the rule set that contains this line. 365The name must start with a character that is neither 366an ASCII digit nor 367.Dq \- 368nor 369.Dq + . 370To allow for future extensions, 371an unquoted name should not contain characters from the set 372.Dq Ql "!$%&'()*,/:;<=>?@[\]^`{|}~" . 373.It FROM 374Gives the first year in which the rule applies. 375Any signed integer year can be supplied; the proleptic Gregorian calendar 376is assumed, with year 0 preceding year 1. 377Rules can describe times that are not representable as time values, 378with the unrepresentable times ignored; this allows rules to be portable 379among hosts with differing time value types. 380.It TO 381Gives the final year in which the rule applies. 382The word 383.Cm maximum 384(or an abbreviation) means the indefinite future, and the word 385.Cm only 386(or an abbreviation) 387may be used to repeat the value of the 388.Ar FROM 389field. 390.It \- 391Is a reserved field and should always contain 392.Ql \- 393for compatibility with older versions of 394.Nm . 395It was previously known as the 396.Ar TYPE 397field, which could contain values to allow a 398separate script to further restrict in which 399.Dq types 400of years the rule would apply. 401.It IN 402Names the month in which the rule takes effect. 403Month names may be abbreviated as mentioned previously; 404for example, January can appear as 405.Dq January , 406.Dq JANU 407or 408.Dq Ja , 409but not as 410.Dq j 411which would be ambiguous with both June and July. 412.It ON 413Gives the day on which the rule takes effect. 414Recognized forms include: 415.Bl -tag -compact -width "Sun<=25" 416.It 5 417the fifth of the month 418.It lastSun 419the last Sunday in the month 420.It lastMon 421the last Monday in the month 422.It Sun>=8 423first Sunday on or after the eighth 424.It Sun<=25 425last Sunday on or before the 25th 426.El 427.Pp 428A weekday name (e.g., 429.Ql "Sunday" ) 430or a weekday name preceded by 431.Dq "last" 432(e.g., 433.Ql "lastSunday" ) 434may be abbreviated as mentioned previously, 435e.g., 436.Dq Su 437for Sunday and 438.Dq lastsa 439for the last Saturday. 440There must be no white space characters within the 441.Ar ON 442field. 443The 444.Dq <= 445and 446.Dq >= 447constructs can result in a day in the neighboring month; 448for example, the IN-ON combination 449.Dq "Oct Sun>=31" 450stands for the first Sunday on or after October 31, 451even if that Sunday occurs in November. 452.It AT 453Gives the time of day at which the rule takes effect, 454relative to 00:00, the start of a calendar day. 455Recognized forms include: 456.Bl -tag -compact -width "00:19:32.13" 457.It 2 458time in hours 459.It 2:00 460time in hours and minutes 461.It 01:28:14 462time in hours, minutes, and seconds 463.It 00:19:32.13 464time with fractional seconds 465.It 12:00 466midday, 12 hours after 00:00 467.It 15:00 4683 PM, 15 hours after 00:00 469.It 24:00 470end of day, 24 hours after 00:00 471.It 260:00 472260 hours after 00:00 473.It \-2:30 4742.5 hours before 00:00 475.It \- 476equivalent to 0 477.El 478.Pp 479Although 480.Nm 481rounds times to the nearest integer second 482(breaking ties to the even integer), the fractions may be useful 483to other applications requiring greater precision. 484The source format does not specify any maximum precision. 485Any of these forms may be followed by the letter 486.Ql w 487if the given time is local or 488.Dq "wall clock" 489time, 490.Ql s 491if the given time is standard time without any adjustment for daylight saving, 492or 493.Ql u 494(or 495.Ql g 496or 497.Ql z ) 498if the given time is universal time; 499in the absence of an indicator, 500local (wall clock) time is assumed. 501These forms ignore leap seconds; for example, 502if a leap second occurs at 00:59:60 local time, 503.Ql "1:00" 504stands for 3601 seconds after local midnight instead of the usual 3600 seconds. 505The intent is that a rule line describes the instants when a 506clock/calendar set to the type of time specified in the 507.Ar AT 508field would show the specified date and time of day. 509.It SAVE 510Gives the amount of time to be added to local standard time when the rule is in 511effect, and whether the resulting time is standard or daylight saving. 512This field has the same format as the 513.Ar AT 514field 515except with a different set of suffix letters: 516.Ql s 517for standard time and 518.Ql d 519for daylight saving time. 520The suffix letter is typically omitted, and defaults to 521.Ql s 522if the offset is zero and to 523.Ql d 524otherwise. 525Negative offsets are allowed; in Ireland, for example, daylight saving 526time is observed in winter and has a negative offset relative to 527Irish Standard Time. 528The offset is merely added to standard time; for example, 529.Nm 530does not distinguish a 10:30 standard time plus an 0:30 531.Ar SAVE 532from a 10:00 standard time plus a 1:00 533.Ar SAVE . 534.It LETTER/S 535Gives the 536.Dq "variable part" 537(for example, the 538.Dq "S" 539or 540.Dq "D" 541in 542.Dq "EST" 543or 544.Dq "EDT" ) 545of time zone abbreviations to be used when this rule is in effect. 546If this field is 547.Ql \- , 548the variable part is null. 549.El 550.Pp 551A zone line has the form 552.Bd -literal -offset indent 553Zone NAME STDOFF RULES FORMAT [UNTIL] 554.Ed 555.Pp 556For example: 557.Bd -literal -offset indent 558Zone Asia/Amman 2:00 Jordan EE%sT 2017 Oct 27 01:00 559.Ed 560.Pp 561The fields that make up a zone line are: 562.Bl -tag -width "STDOFF" 563.It NAME 564The name of the timezone. 565This is the name used in creating the time conversion information file for the 566timezone. 567It should not contain a file name component 568.Dq ".\&" 569or 570.Dq ".." ; 571a file name component is a maximal substring that does not contain 572.Dq "/" . 573.It STDOFF 574The amount of time to add to UT to get standard time, 575without any adjustment for daylight saving. 576This field has the same format as the 577.Ar AT 578and 579.Ar SAVE 580fields of rule lines, except without suffix letters; 581begin the field with a minus sign if time must be subtracted from UT. 582.It RULES 583The name of the rules that apply in the timezone or, 584alternatively, a field in the same format as a rule-line 585.Ar SAVE 586field, 587giving the amount of time to be added to local standard time 588and whether the resulting time is standard or daylight saving. 589Standard time applies if this field is 590.Ql \- 591or for timestamps occurring before any rule takes effect. 592When an amount of time is given, only the sum of standard time and 593this amount matters. 594.It FORMAT 595The format for time zone abbreviations. 596The pair of characters 597.Ql %s 598shows where to put the time zone abbreviation's variable part, 599which is taken from the 600.Ar LETTER/S 601field of the corresponding rule; 602any timestamps that precede the earliest rule use the 603.Ar LETTER/S 604of the earliest standard-time rule (which in this case must exist). 605Alternatively, a format can use the pair of characters 606.Ql %z 607to stand for the UT offset in the form 608.Ar \(+- hh , 609.Ar \(+- hhmm , 610or 611.Ar \(+- hhmmss , 612using the shortest form that does not lose information, where 613.Ar hh , 614.Ar mm , 615and 616.Ar ss 617are the hours, minutes, and seconds east (+) or west (\-) of UT. 618Alternatively, 619a slash (/) 620separates standard and daylight abbreviations. 621To conform to POSIX, a time zone abbreviation should contain only 622alphanumeric ASCII characters, 623.Ql "+" 624and 625.Ql "\-". 626By convention, the time zone abbreviation 627.Ql "\-00" 628is a placeholder that means local time is unspecified. 629.It UNTIL 630The time at which the UT offset or the rule(s) change for a location. 631It takes the form of one to four fields 632.Ar YEAR Op Ar MONTH Op Ar DAY Op Ar TIME . 633If this is specified, 634the time zone information is generated from the given UT offset 635and rule change until the time specified, which is interpreted using 636the rules in effect just before the transition. 637The month, day, and time of day have the same format as the 638.Ar IN , 639.Ar ON , 640and 641.Ar AT 642fields of a rule; trailing fields can be omitted, and default to the 643earliest possible value for the missing fields. 644.IP 645The next line must be a 646.Dq "continuation" 647line; this has the same form as a zone line except that the 648string 649.Dq "Zone" 650and the name are omitted, as the continuation line will 651place information starting at the time specified as the 652.Dq "until" 653information in the previous line in the file used by the previous line. 654Continuation lines may contain 655.Dq "until" 656information, just as zone lines do, indicating that the next line is a further 657continuation. 658.El 659.Pp 660If a zone changes at the same instant that a rule would otherwise take 661effect in the earlier zone or continuation line, the rule is ignored. 662A zone or continuation line 663.Ar L 664with a named rule set starts with standard time by default: 665that is, any of 666.Ar L 's 667timestamps preceding 668.Ar L 's 669earliest rule use the rule in effect after 670.Ar L 's 671first transition into standard time. 672In a single zone it is an error if two rules take effect at the same 673instant, or if two zone changes take effect at the same instant. 674.Pp 675If a continuation line subtracts 676.Ar N 677seconds from the UT offset after a transition that would be 678interpreted to be later if using the continuation line's UT offset and 679rules, the 680.Dq "until" 681time of the previous zone or continuation line is interpreted 682according to the continuation line's UT offset and rules, and any rule 683that would otherwise take effect in the next 684.Ar N 685seconds is instead assumed to take effect simultaneously. 686For example: 687.Bd -literal -offset indent 688# Rule NAME FROM TO - IN ON AT SAVE LETTER/S 689Rule US 1967 2006 - Oct lastSun 2:00 0 S 690Rule US 1967 1973 - Apr lastSun 2:00 1:00 D 691# Zone NAME STDOFF RULES FORMAT [UNTIL] 692Zone America/Menominee -5:00 - EST 1973 Apr 29 2:00 693 -6:00 US C%sT 694.Ed 695Here, an incorrect reading would be there were two clock changes on 1973-04-29, 696the first from 02:00 EST (\-05) to 01:00 CST (\-06) according to the 697.q "until" 698value in the zone line, 699and the second an hour later from 02:00 CST (\-06) to 03:00 CDT (\-05) 700according to the values in the April rule line. 701However, 702.Nm 703interprets this more sensibly as a single transition from 02:00 EST (\-05) to 70402:00 CDT (\-05). 705.Pp 706A link line has the form 707.Bd -literal -offset indent 708Link TARGET LINK-NAME 709.Ed 710.Pp 711For example: 712.Bd -literal -offset indent 713Link Europe/Istanbul Asia/Istanbul 714.Ed 715.Pp 716The 717.Ar TARGET 718field should appear as the 719.Ar NAME 720field in some zone line or as the 721.Ar LINK-NAME 722field in some link line. 723The 724.Ar LINK-NAME 725field is used as an alternative name for that zone; 726it has the same syntax as a zone line's 727.Ar NAME 728field. 729Links can chain together, although the behavior is unspecified if a 730chain of one or more links does not terminate in a Zone name. 731A link line can appear before the line that defines the link target. 732For example: 733.Bd -literal -offset indent 734Link Greenwich G_M_T 735Link Etc/GMT Greenwich 736Zone Etc/GMT\0\00\0\0\-\0\0GMT 737.Ed 738.Pp 739The two links are chained together, and G_M_T, Greenwich, and Etc/GMT 740all name the same zone. 741.Pp 742Except for continuation lines, 743lines may appear in any order in the input. 744However, the behavior is unspecified if multiple zone or link lines 745define the same name. 746.Pp 747The file that describes leap seconds can have leap lines and an 748expiration line. 749Leap lines have the following form: 750.Bd -literal -offset indent 751Leap YEAR MONTH DAY HH:MM:SS CORR R/S 752.Ed 753.Pp 754For example: 755.Bd -literal -offset indent 756Leap 2016 Dec 31 23:59:60 + S 757.Ed 758.Pp 759The 760.Ar YEAR , 761.Ar MONTH , 762.Ar DAY , 763and 764.Ar HH:MM:SS 765fields tell when the leap second happened. 766The 767.Ar CORR 768field 769should be 770.Ql "+" 771if a second was added 772or 773.Ql "\-" 774if a second was skipped. 775The 776.Ar R/S 777field 778should be (an abbreviation of) 779.Dq "Stationary" 780if the leap second time given by the other fields should be interpreted as UTC 781or 782(an abbreviation of) 783.Dq "Rolling" 784if the leap second time given by the other fields should be interpreted as 785local (wall clock) time. 786.Pp 787Rolling leap seconds would let one see 788Times Square ball drops where there'd be a 789.Dq "3... 2... 1... leap... Happy New Year" 790countdown, placing the leap second at 791midnight New York time rather than midnight UTC. 792Although stationary leap seconds are the common practice, 793rolling leap seconds can be useful in specialized applications 794like SMPTE timecodes that may prefer to put leap second 795discontinuities at the end of a local broadcast day. 796However, rolling leap seconds are not supported if the 797.Fl r 798option is used. 799.Pp 800The expiration line, if present, has the form: 801.Bd -literal -offset indent 802Expires YEAR MONTH DAY HH:MM:SS 803.Ed 804.Pp 805For example: 806.Bd -literal -offset indent 807Expires 2020 Dec 28 00:00:00 808.Ed 809.Pp 810The 811.Ar YEAR , 812.Ar MONTH , 813.Ar DAY , 814and 815.Ar HH:MM:SS 816fields give the expiration timestamp in UTC for the leap second table. 817.Sh "EXTENDED EXAMPLE" 818Here is an extended example of 819.Nm 820input, intended to illustrate many of its features. 821.Bd -literal -offset indent 822# Rule NAME FROM TO \- IN ON AT SAVE LETTER/S 823Rule Swiss 1941 1942 \- May Mon>=1 1:00 1:00 S 824Rule Swiss 1941 1942 \- Oct Mon>=1 2:00 0 \- 825 826Rule EU 1977 1980 \- Apr Sun>=1 1:00u 1:00 S 827Rule EU 1977 only \- Sep lastSun 1:00u 0 \- 828Rule EU 1978 only \- Oct 1 1:00u 0 \- 829Rule EU 1979 1995 \- Sep lastSun 1:00u 0 \- 830Rule EU 1981 max \- Mar lastSun 1:00u 1:00 S 831Rule EU 1996 max \- Oct lastSun 1:00u 0 \- 832 833# Zone NAME STDOFF RULES FORMAT [UNTIL] 834Zone Europe/Zurich 0:34:08 \- LMT 1853 Jul 16 835 0:29:45.50 \- BMT 1894 Jun 836 1:00 Swiss CE%sT 1981 837 1:00 EU CE%sT 838 839Link Europe/Zurich Europe/Vaduz 840.Ed 841.Pp 842In this example, the EU rules are for the European Union 843and for its predecessor organization, the European Communities. 844The timezone is named Europe/Zurich and it has the alias Europe/Vaduz. 845This example says that Zurich was 34 minutes and 8 846seconds east of UT until 1853-07-16 at 00:00, when the legal offset 847was changed to 8487\(de26\(fm22.50\(sd, 849which works out to 0:29:45.50; 850.Nm 851treats this by rounding it to 0:29:46. 852After 1894-06-01 at 00:00 the UT offset became one hour 853and Swiss daylight saving rules (defined with lines beginning with 854.Dq "Rule Swiss") 855apply. 856From 1981 to the present, EU daylight saving rules have 857applied, and the UTC offset has remained at one hour. 858.Pp 859In 1941 and 1942, daylight saving time applied from the first Monday 860in May at 01:00 to the first Monday in October at 02:00. 861The pre-1981 EU daylight-saving rules have no effect 862here, but are included for completeness. 863Since 1981, daylight 864saving has begun on the last Sunday in March at 01:00 UTC. 865Until 1995 it ended the last Sunday in September at 01:00 UTC, 866but this changed to the last Sunday in October starting in 1996. 867.Pp 868For purposes of display, 869.Dq "LMT" 870and 871.Dq "BMT" 872were initially used, respectively. 873Since 874Swiss rules and later EU rules were applied, the time zone abbreviation 875has been CET for standard time and CEST for daylight saving 876time. 877.Sh FILES 878.Bl -tag -width "/usr/share/zoneinfo" 879.It Pa /etc/localtime 880Default local timezone file. 881.It Pa /usr/share/zoneinfo 882Default timezone information directory. 883.El 884.Sh NOTES 885For areas with more than two types of local time, 886you may need to use local standard time in the 887.Ar AT 888field of the earliest transition time's rule to ensure that 889the earliest transition time recorded in the compiled file is correct. 890.Pp 891If, 892for a particular timezone, 893a clock advance caused by the start of daylight saving 894coincides with and is equal to 895a clock retreat caused by a change in UT offset, 896.Nm 897produces a single transition to daylight saving at the new UT offset 898without any change in local (wall clock) time. 899To get separate transitions 900use multiple zone continuation lines 901specifying transition instants using universal time. 902.Sh SEE ALSO 903.Xr tzfile 5 , 904.Xr zdump 8 905