1.\" $NetBSD: zic.8,v 1.44 2023/12/06 20:01:44 christos Exp $ 2.\" @(#)zic.8 8.6 3.\" This file is in the public domain, so clarified as of 4.\" 2009-05-17 by Arthur David Olson. 5.\" .TH zic 8 6.Dd December 6, 2023 7.Dt ZIC 8 8.Os 9.Sh NAME 10.Nm zic 11.Nd timezone compiler 12.Sh SYNOPSIS 13.Nm 14.Op Fl \-version 15.Op Fl \-help 16.Op Fl b 17.Op Fl d Ar directory 18.Op Fl L Ar leapsecondfilename 19.Op Fl l Ar localtime 20.Op Fl p Ar posixrules 21.Op Fl s 22.Op Fl t Ar file 23.Op Fl v 24.Op Fl y Ar command 25.Op Ar Filename ... 26.Sh DESCRIPTION 27The 28.Nm 29program reads text from the file(s) named on the command line 30and creates the timezone information format (TZif) files 31specified in this input. 32If a 33.Ar filename 34is 35.Ar \&- , 36standard input is read. 37.Pp 38.Sh OPTIONS 39.Bl -tag -width XXXXXXXXXX -compact 40.It Fl \-version 41Output version information and exit. 42.It Fl \-help 43Output short usage message and exit. 44.It Fl b Ar bloat 45Output backward-compatibility data as specified by 46.Ar bloat . 47If 48.Ar bloat 49is 50.Dv fat , 51generate additional data entries that work around potential bugs or 52incompatibilities in older software, such as software that mishandles 53the 64-bit generated data. 54If 55.Ar bloat 56is 57.Dv slim , 58keep the output files small; this can help check for the bugs 59and incompatibilities. 60The default is 61.Dv slim , 62as software that mishandles 64-bit data typically 63mishandles timestamps after the year 2038 anyway. 64Also see the 65.Fl r 66option for another way to alter output size. 67.It Fl d Ar directory 68Create time conversion information files in the named directory rather than 69in the standard directory named below. 70.It Fl l Ar timezone 71Use the 72.Ar timezone 73as local time. 74.Nm 75will act as if the input contained a link line of the form 76.Dl Link timezone localtime 77If 78.Ar timezone 79is 80.Dv \&- , 81any already-existing link is removed. 82.It Fl L Ar leapsecondfilename 83Read leap second information from the file with the given name. 84If this option is not used, 85no leap second information appears in output files. 86.It Fl p Ar timezone 87Use 88.Ar timezone's 89rules when handling POSIX-format 90TZ strings like 91.Qq EET\&-2EEST 92that lack transition rules. 93.Nm 94will act as if the input contained a link line of the form 95.Dl Link timezone posixrules 96.Pp 97Unless 98.Ar timezone 99is 100.Dq \&- , 101this option is obsolete and poorly supported. 102Among other things it should not be used for timestamps after the year 2037, 103and it should not be combined with 104.Fl b Ar slim 105if 106.Va timezone's 107transitions are at standard time or Universal Time (UT) instead of local time. 108If 109.Ar timezone 110is 111.Dv \&- , 112any already-existing link is removed. 113.It Fl r Op Ar @lo / Op Ar @hi 114Limit the applicability of output files 115to timestamps in the range from 116.Ar lo 117(inclusive) to 118.Ar hi 119(exclusive), where 120.Ar lo 121and 122.Ar hi 123are possibly signed decimal counts of seconds since the Epoch 124(1970-01-01 00:00:00 UTC). 125Omitted counts default to extreme values. 126The output files use UT offset 0 and abbreviation 127.q "\*-00" 128in place of the omitted timestamp data. 129For example, 130.Bd -literal 131zic -r @0 132.Ed 133omits data intended for negative timestamps (i.e., before the Epoch), and 134.Bd -literal 135zic -r @0/@2147483648 136.Ed 137outputs data intended only for nonnegative timestamps that fit into 13831-bit signed integers. 139Or using 140.Xr date 1 , 141.Bd -literal 142zic -r @$(date +%s) 143.Ed 144omits data intended for past timestamps. 145Although this option typically reduces the output file's size, 146the size can increase due to the need to represent the timestamp range 147boundaries, particularly if 148.Ar hi 149causes a TZif file to contain explicit entries for 150.Ar pre- hi 151transitions rather than concisely representing them 152with an extended POSIX TZ string. 153Also see the 154.Fl b Ar slim 155option for another way to shrink output size. 156.It Fl R Ar @hi 157Generate redundant trailing explicit transitions for timestamps 158that occur less than 159Ar hi 160seconds since the Epoch, even though the transitions could be 161more concisely represented via the extended POSIX TZ string. 162This option does not affect the represented timestamps. 163Although it accommodates nonstandard TZif readers 164that ignore the extended POSIX TZ string, 165it increases the size of the altered output files. 166.It Fl t Ar file 167When creating local time information, put the configuration link in 168the named file rather than in the standard location. 169.It Fl v 170Be more verbose, and complain about the following situations: 171.Bl -dash 172.It 173+The input specifies a link to a link, 174something not supported by some older parsers, including 175.Nm 176itself through release 2022e. 177.It 178A year that appears in a data file is outside the range 179of representable years. 180.It 181A time of 24:00 or more appears in the input. 182Pre-1998 versions of 183.Nm 184prohibit 24:00, and pre-2007 versions prohibit times greater than 24:00. 185.It 186A rule goes past the start or end of the month. 187Pre-2004 versions of 188.Nm 189prohibit this. 190.It 191A time zone abbreviation uses a 192.Dv %z 193format. 194Pre-2015 versions of 195.Nm 196do not support this. 197.It 198A timestamp contains fractional seconds. 199Pre-2018 versions of 200.Nm 201do not support this. 202.It 203The input contains abbreviations that are mishandled by pre-2018 versions of 204.Nm 205due to a longstanding coding bug. 206These abbreviations include 207.Qq L 208for 209.Qq Link , 210.Qq mi 211for 212.Qq min , 213.Qq Sa 214for 215.Qq Sat , 216and 217.Qq Su 218for 219.Qq Sun . 220.It 221The output file does not contain all the information about the 222long-term future of a timezone, because the future cannot be summarized as 223an extended POSIX TZ string. 224For example, as of 2023 this problem 225occurs for Morocco's daylight-saving rules, as 226on predictions for when Ramadan will be observed, something that 227an extended POSIX TZ string cannot represent. 228.It 229The output contains data that may not be handled properly by client 230code designed for older 231.Xr zic 8 232output formats. 233These compatibility issues affect only timestamps 234before 1970 or after the start of 2038. 235.It 236The output contains a truncated leap second table, 237which can cause some older TZif readers to misbehave. 238This can occur if the 239.Fl L 240option is used, and either an Expires line is present or 241the 242.Fl r 243option is also used. 244.It 245The output file contains more than 1200 transitions, 246which may be mishandled by some clients. 247The current reference client supports at most 2000 transitions; 248pre-2014 versions of the reference client support at most 1200 249transitions. 250.It 251A time zone abbreviation has fewer than 3 or more than 6 characters. 252POSIX requires at least 3, and requires implementations to support 253at least 6. 254.It 255An output file name contains a byte that is not an ASCII letter, 256.Qq - , 257.Qq / , 258or 259.Qq _ ; 260or it 261or it contains a file name component that contains more than 14 bytes 262or that starts with 263.Qq - . 264.El 265.El 266.Pp 267Input files should be text files, that is, they should be a series of 268zero or more lines, each ending in a newline byte and containing at 269most 2048 bytes counting the newline, and without any 270.Dv NUL 271bytes. 272The input text's encoding 273is typically UTF-8 or ASCII; it should have a unibyte representation 274for the POSIX Portable Character Set (PPCS) 275.Rs 276.%U https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap06.html 277.Re 278and the encoding's non-unibyte characters should consist entirely of 279non-PPCS bytes. 280Non-PPCS characters typically occur only in comments: 281although output file names and time zone abbreviations can contain 282nearly any character, other software will work better if these are 283limited to the restricted syntax described under the 284.Op v 285option. 286.Pp 287Input lines are made up of fields. 288Fields are separated from one another by one or more white space characters. 289The white space characters are space, form feed, carriage return, newline, 290tab, and vertical tab. 291Leading and trailing white space on input lines is ignored. 292An unquoted sharp character (#) in the input introduces a comment which extends 293to the end of the line the sharp character appears on. 294White space characters and sharp characters may be enclosed in double 295quotes 296.Pq \&" 297.\" XXX " 298if they're to be used as part of a field. 299Any line that is blank (after comment stripping) is ignored. 300Nonblank lines are expected to be of one of three types: 301rule lines, zone lines, and link lines. 302.Pp 303Names must be in English and are case insensitive. 304They appear in several contexts, and include month and weekday names 305and keywords such as 306.Qq maximum , 307.Qq only , 308.Qq Rolling , 309and 310.Qq Zone . 311A name can be abbreviated by omitting all but an initial prefix; any 312abbreviation must be unambiguous in context. 313.Pp 314A rule line has the form 315.Pp 316.Bl -column -compact -offset indent "Rule" "NAME" "FROM" "1995" "\&*" "Apr" "lastSun" "2:00w" "1:00d" "LETTER/S" 317.It Rule NAME FROM TO \&- IN ON AT SAVE LETTER/S 318.El 319.Pp 320For example: 321.Pp 322.Bl -column -compact -offset indent "Rule" "NAME" "FROM" "1995" "\&*" "Apr" "lastSun" "2:00w" "1:00d" "LETTER/S" 323.It Rule US 1967 1973 \&- Apr lastSun 2:00w 1:00d D 324.El 325.Pp 326The fields that make up a rule line are: 327.Bl -tag -width "LETTER/S" 328.It NAME 329Gives the name of the rule set that contains this line. 330The name must start with a character that is neither 331an ASCII digit nor 332.Ar \&- 333nor 334.Ar + . 335To allow for future extensions, 336an unquoted name should not contain characters from the set 337.Ar !$%&'()*,/:;<=>?@[\e]^`{|}~ . 338.It FROM 339Gives the first year in which the rule applies. 340Any signed integer year can be supplied; the proleptic Gregorian calendar 341is assumed, with year 0 preceding year 1. 342The word 343.Em minimum 344(or an abbreviation) means the indefinite past. 345The word 346.Em maximum 347(or an abbreviation) means the indefinite future. 348Rules can describe times that are not representable as time values, 349with the unrepresentable times ignored; this allows rules to be portable 350among hosts with differing time value types. 351.It TO 352Gives the final year in which the rule applies. 353In addition to 354.Em minimum 355and 356.Em maximum 357(as above), 358the word 359.Em only 360(or an abbreviation) 361may be used to repeat the value of the 362.Em FROM 363field. 364.It \&- 365should be 366.Qq \&- 367for compatibility with older versions of 368.Nm . 369It was previously known as the 370.Em TYPE 371field, which could contain values to allow a 372separate script to further restrict in which 373.Em types 374of years the rule would apply. 375.It IN 376Names the month in which the rule takes effect. 377Month names may be abbreviated. 378.It ON 379Gives the day on which the rule takes effect. 380Recognized forms include: 381.Pp 382.Bl -tag -width lastSun -compact -offset indent 383.It 5 384the fifth of the month 385.It lastSun 386the last Sunday in the month 387.It lastMon 388the last Monday in the month 389.It Sun\*[Ge]8 390first Sunday on or after the eighth 391.It Sun\*[Le]25 392last Sunday on or before the 25th 393.El 394.Pp 395Names of days of the week may be abbreviated or spelled out in full. 396A weekday name (e.g., 397.Qq Sunday ) 398or a weekday name preceded by 399.Qq last 400(e.g., 401.Qq lastSunday ) 402may be abbreviated or spelled out in full. 403There must be no white space characters within the 404.Em ON 405field. 406The 407.Qq <= 408and 409.Qq >= 410constructs can result in a day in the neighboring month; 411for example, the IN-ON combination 412.Qq "Oct Sun>=31" 413tands for the first Sunday on or after October 31, 414even if that Sunday occurs in November. 415.It AT 416Gives the time of day at which the rule takes effect, 417relative to 00:00, the start of a calendar day. 418Recognized forms include: 419.Pp 420.Bl -tag -width "00X19X32X13" -compact -offset indent 421.It 2 422time in hours 423.It 2:00 424time in hours and minutes 425.It 01:28:14 426time in hours, minutes, and seconds 427.It 00:19:32.13 428time with fractional seconds 429.It 12:00 430midday, 12 hours after 00:00 431.It 15:00 4323 PM, 15 hours after 00:00 433.It 24:00 434end of day, 24 hours after 00:00 435.It 260:00 436260 hours after 00:00 437.It \-2:30 4382.5 hours before 00:00 439.It \- 440equivalent to 0 441.El 442.Pp 443Although 444.I zic 445rounds times to the nearest integer second 446(breaking ties to the even integer), the fractions may be useful 447to other applications requiring greater precision. 448The source format does not specify any maximum precision. 449Any of these forms may be followed by the letter 450.Em w 451if the given time is local or 452.Qq wall clock 453time, 454.Em s 455if the given time is standard time without any adjustment for daylight saving, 456or 457.Em u 458(or 459.Em g 460or 461.Em z ) 462if the given time is universal time; 463in the absence of an indicator, 464local (wall clock) time is assumed. 465These forms ignore leap seconds; for example, 466if a leap second occurs at 00:59:60 local time, 467.q "1:00" 468stands for 3601 seconds after local midnight instead of the usual 3600 seconds. 469The intent is that a rule line describes the instants when a 470clock/calendar set to the type of time specified in the 471.Em AT 472field would show the specified date and time of day. 473.It SAVE 474Gives the amount of time to be added to local standard time when the rule is in 475effect, and whether the resulting time is standard or daylight saving. 476This field has the same format as the 477.Em AT 478field 479.Em s 480for standard time and 481.Em d 482for daylight saving time. 483The suffix letter is typically omitted, and defaults to 484.Em s 485if the offset is zero and to 486.Em d 487otherwise. 488Negative offsets are allowed; in Ireland, for example, daylight saving 489time is observed in winter and has a negative offset relative to 490Irish Standard Time. 491The offset is merely added to standard time; for example, 492.Nm 493does not distinguish a 10:30 standard time plus an 0:30 494.Em SAVE 495from a 10:00 standard time plus a 1:00 496.Em SAVE . 497.It LETTER/S 498Gives the 499.Qq variable part 500(for example, the 501.Qq S 502or 503.Qq D 504in 505.Qq EST 506or 507.Qq EDT ) 508of time zone abbreviations to be used when this rule is in effect. 509If this field is 510.Em \&- , 511the variable part is null. 512.El 513.Pp 514A zone line has the form: 515.Pp 516.Bl -column -compact -offset indent "Zone" "Asia/Amman" "STDOFF" "RULES/SAVE" "FORMAT" "[UNTIL]" 517Zone NAME STDOFF RULES/SAVE FORMAT [UNTIL] 518.El 519.Pp 520For example: 521.Pp 522.Bl -column -compact -offset indent "Zone" "Asia/Amman" "STDOFF" "RULES/SAVE" "FORMAT" "[UNTIL"] 523Zone Asia/Amman 2:00 Jordan EE%sT 2017 Oct 27 1:00 524.El 525.Pp 526The fields that make up a zone line are: 527.Bl -tag -width "RULES/SAVE" 528.It NAME 529The name of the timezone. 530This is the name used in creating the time conversion information file for the 531timezone. 532It should not contain a file name component 533.Qq . 534or 535.Qq .. ; 536a file name component is a maximal substring that does not contain 537.Qq / . 538.It STDOFF 539The amount of time to add to UT to get standard time, 540without any adjustment for daylight saving. 541This field has the same format as the 542.Em AT 543and 544.Em SAVE 545fields of rule lines, except without suffix letters; 546begin the field with a minus sign if time must be subtracted from UT. 547.It RULES 548The name of the rules that apply in the timezone or, 549alternatively, a field in the same format as a rule-line SAVE column, 550giving the amount of time to be added to local standard time 551and whether the resulting time is standard or daylight saving. 552If this field is 553.Em \&- 554then standard time always applies. 555When an amount of time is given, only the sum of standard time and 556this amount matters. 557.It FORMAT 558The format for time zone abbreviations. 559The pair of characters 560.Em %s 561is used to show where the 562.Qq variable part 563of the time zone abbreviation goes. 564Alternatively, a format can use the pair of characters 565.Em %z 566+to stand for the UT offset in the form 567.Em \(+- hh , 568.Em \(+- hhmm , 569or 570.Em \(+- hhmmss , 571using the shortest form that does not lose information, where 572.Em hh , 573.Em mm , 574and 575.Em ss 576are the hours, minutes, and seconds east (+) or west (\-) of UT. 577Alternatively, 578a slash 579.Pq \&/ 580separates standard and daylight abbreviations. 581To conform to POSIX, a time zone abbreviation should contain only 582alphanumeric ASCII characters, 583.Qq + 584and 585.Qq \&- . 586By convention, the time zone abbreviation 587.Qq \&-00 588is a placeholder that means local time is unspecified. 589.It UNTIL 590The time at which the UT offset or the rule(s) change for a location. 591It takes the form of one to four fields YEAR [MONTH [DAY [TIME]]]. 592If this is specified, 593the time zone information is generated from the given UT offset 594and rule change until the time specified, which is interpreted using 595the rules in effect just before the transition. 596The month, day, and time of day have the same format as the IN, ON, and AT 597fields of a rule; trailing fields can be omitted, and default to the 598earliest possible value for the missing fields. 599.Pp 600The next line must be a 601.Qq continuation 602line; this has the same form as a zone line except that the 603string 604.Qq Zone 605and the name are omitted, as the continuation line will 606place information starting at the time specified as the 607.Em until 608information in the previous line in the file used by the previous line. 609Continuation lines may contain 610.Em until 611information, just as zone lines do, indicating that the next line is a further 612continuation. 613.El 614.Pp 615If a zone changes at the same instant that a rule would otherwise take 616effect in the earlier zone or continuation line, the rule is ignored. 617A zone or continuation line 618.I L 619with a named rule set starts with standard time by default: 620that is, any of 621.IR L 's 622timestamps preceding 623.IR L 's 624earliest rule use the rule in effect after 625.IR L 's 626first transition into standard time. 627In a single zone it is an error if two rules take effect at the same 628instant, or if two zone changes take effect at the same instant. 629.Pp 630If a continuation line subtracts 631.Dv N 632seconds from the UT offset after a transition that would be 633interpreted to be later if using the continuation line's UT offset and 634rules, the 635.Em until 636time of the previous zone or continuation line is interpreted 637according to the continuation line's UT offset and rules, and any rule 638that would otherwise take effect in the next 639.Dv N 640seconds is instead assumed to take effect simultaneously. 641For example: 642.Pp 643.Bl -column -compact -offset indent "# Rule" "NAME" "FROM" "2006" "\&-" "Oct" "lastSun" "1:00" "SAVE" "LETTER/S" 644.It # Rule NAME FROM TO \&- IN ON AT SAVE LETTER/S 645.It Rule US 1967 2006 \&- Oct lastSun 2:00 0 S 646.It Rule US 1967 1973 \&- Apr lastSun 2:00 1:00 D 647.El 648.Bl -column -compact -offset indent "# Zone" "America/Menominee" "STDOFF" "RULES" "FORMAT" "[UNTIL]" 649.It # Zone NAME STDOFF RULES FORMAT [UNTIL] 650.It Zone America/Menominee \&-5:00 \&- EST 1973 Apr 29 2:00 651.It \& \& \&-6:00 US C%sT 652.El 653.Pp 654Here, an incorrect reading would be there were two clock changes on 1973-04-29, 655the first from 02:00 EST (\&-05) to 01:00 CST (\&-06), 656and the second an hour later from 02:00 CST (\&-06) to 03:00 CDT (\&-05). 657However, 658.Nm 659interprets this more sensibly as a single transition from 02:00 CST (\&-05) to 66002:00 CDT (\&-05). 661.Pp 662A link line has the form 663.Pp 664.Bl -column -compact -offset indent "Link" "Europe/Istanbul" "Asia/Istanbul" 665.It Link TARGET LINK-NAME 666.El 667.Pp 668For example: 669.Pp 670.Bl -column -compact -offset indent "Link" "Europe/Istanbul" "Asia/Istanbul" 671.It Link Europe/Istanbul Asia/Istanbul 672.El 673.Pp 674The 675.Em TARGET 676field should appear as the 677.Em NAME 678field in some zone line. 679field in some zone line or as the 680.Em LINK-NAME 681field in some link line. 682The 683.Em LINK-NAME 684field is used as an alternative name for that zone; 685it has the same syntax as a zone line's 686.Em NAME 687field. 688Links can chain together, although the behavior is unspecified if a 689chain of one or more links does not terminate in a Zone name. 690A link line can appear before the line that defines the link target. 691For example: 692.Bl -column -offset indent "Link" "Greenwich" "Greenwich" 693.It Link Greenwich G_M_T 694.It Link Etc/GMT Greenwich 695.It Zone Etc/GMT 0 - GMT 696.El 697.Pp 698The two links are chained together, and G_M_T, Greenwich, and Etc/GMT 699all name the same zone. 700.Pp 701Except for continuation lines, 702lines may appear in any order in the input. 703However, the behavior is unspecified if multiple zone or link lines 704define the same name. 705.Pp 706The file that describes leap seconds can have leap lines and an 707expiration line. 708Leap lines have the following form: 709.Pp 710.Bl -column -compat -offset indent "Leap" "YEAR" "MONTH" "DAY" "HH:MM:SS" "CORR""R/S" 711.It Leap YEAR MONTH DAY HH:MM:SS CORR R/S 712.El 713.Pp 714For example: 715.Pp 716.Bl -column -compat -offset indent "Leap" "YEAR" "MONTH" "DAY" "HH:MM:SS" "CORR""R/S" 717.It Leap 2016 Dec 31 23:59:60 + S 718.El 719.Pp 720The 721.Em YEAR , 722.Em MONTH , 723.Em DAY , 724and 725.Em HH:MM:SS 726fields tell when the leap second happened. 727The 728.Em CORR 729field 730should be 731.Qq \&+ 732if a second was added 733or 734.Qq \&- 735if a second was skipped. 736The 737.Em R/S 738field 739should be (an abbreviation of) 740.Qq Stationary 741if the leap second time given by the other fields should be interpreted as UTC 742or 743(an abbreviation of) 744.Qq Rolling 745if the leap second time given by the other fields should be interpreted as 746local (wall clock) time. 747.Pp 748Rolling leap seconds were implemented back when it was not 749clear whether common practice was rolling or stationary, 750with concerns that one would see 751Times Square ball drops where there'd be a 752.Qq 3... 2... 1... leap... Happy New Year 753countdown, placing the leap second at 754midnight New York time rather than midnight UTC. 755However, this countdown style does not seem to have caught on, 756which means rolling leap seconds are not used in practice; 757also, they are not supported if the 758.Fl r 759option is used. 760.Pp 761The expiration line, if present, has the form: 762.Pp 763.Bl -column -compact -offset indent "Expires" "YEAR" "MONTH" "DAY" "HH:MM:SS" 764.It Expires YEAR MONTH DAY HH:MM:SS 765.El 766.Pp 767For example: 768.Pp 769.Bl -column -compact -offset indent "Expires" "YEAR" "MONTH" "DAY" "HH:MM:SS" 770.It Expires 2020 Dec 28 00:00:00 771.El 772.Pp 773The 774.Em YEAR , 775.Em MONTH , 776.Em DAY , 777and 778.Em HH:MM:SS 779fields give the expiration timestamp in UTC for the leap second table. 780.Sh EXTENDED EXAMPLE 781Here is an extended example of 782.Ic zic 783input, intended to illustrate many of its features. 784.Pp 785.Bl -column -compact -offset indent "# Rule" "Swiss" "FROM" "1995" "\&*" "Oct" "lastSun" "1:00u" "SAVE" "LETTER/S" 786.It # Rule NAME FROM TO \&- IN ON AT SAVE LETTER/S 787.It Rule Swiss 1941 1942 \&- May Mon>=1 1:00 1:00 S 788.It Rule Swiss 1941 1942 \&- Oct Mon>=1 2:00 0 - 789.Pp 790.It Rule EU 1977 1980 \&- Apr Sun>=1 1:00u 1:00 S 791.It Rule EU 1977 only \&- Sep lastSun 1:00u 0 - 792.It Rule EU 1978 only \&- Oct 1 1:00u 0 - 793.It Rule EU 1979 1995 \&- Sep lastSun 1:00u 0 - 794.It Rule EU 1981 max \&- Mar lastSun 1:00u 1:00 S 795.It Rule EU 1996 max \&- Oct lastSun 1:00u 0 - 796.El 797.Pp 798.Bl -column -compact -offset indent "# Zone" "Europe/Zurich" "0:29:45.50" "RULES/SAVE" "FORMAT" "UNTIL" 799.It # Zone NAME STDOFF RULES/SAVE FORMAT [UNTIL] 800.It Zone Europe/Zurich 0:34:08 \&- LMT 1853 Jul 16 801.It 0:29:45.50 \&- BMT 1894 Jun 802.It 1:00 Swiss CE%sT 1981 803.It 1:00 EU CE%sT 804.Pp 805.El 806.Bl -column -compact -offset indent "# Zone" "Europe/Zurich" "0:34:08" "RULES/SAVE" "FORMAT" "UNTIL" 807.It Link Europe/Zurich Europe/Vaduz 808.El 809.Pp 810In this example, the EU rules are for the European Union 811and for its predecessor organization, the European Communities. 812The timezone is named Europe/Zurich and it has the alias Europe/Vaduz. 813This example says that Zurich was 34 minutes and 8 814seconds east of UT until 1853-07-16 at 00:00, when the legal offset 815was changed to 7\(de\|26\(fm\|22.50\(sd; which this works out to 8160:29:45.50; 817.Nm 818treats this by rounding it to 0:29:46. 819After 1894-06-01 at 00:00 the UT offset became one hour 820and Swiss daylight saving rules (defined with lines beginning with 821.Qq "Rule Swiss" 822apply. 823From 1981 to the present, EU daylight saving rules have 824From 1981 to the present, EU daylight saving rules have 825.Pp 826In 1941 and 1942, daylight saving time applied from the first Monday 827in May at 01:00 to the first Monday in October at 02:00. 828The pre-1981 EU daylight-saving rules have no effect 829here, but are included for completeness. 830Since 1981, daylight 831saving has begun on the last Sunday in March at 01:00 UTC. 832Until 1995 it ended the last Sunday in September at 01:00 UTC, 833but this changed to the last Sunday in October starting in 1996. 834.Pp 835For purposes of display, 836.Qq LMT 837and 838.Qq BMT 839were initially used, respectively. 840Since 841Swiss rules and later EU rules were applied, the time zone abbreviation 842has been CET for standard time and CEST for daylight saving 843time. 844.Sh FILES 845Input files use the format described in this section; output files use 846.Xr tzfile 5 847format. 848.Bl -tag -width /usr/share/zoneinfo -compact 849.It Pa /etc/localtime 850Default local timezone file 851.It Pa /usr/share/zoneinfo 852Default timezone information directory 853.El 854.Sh NOTES 855For areas with more than two types of local time, 856you may need to use local standard time in the 857.Em AT 858field of the earliest transition time's rule to ensure that 859the earliest transition time recorded in the compiled file is correct. 860.Pp 861If, 862for a particular timezone, 863a clock advance caused by the start of daylight saving 864coincides with and is equal to 865a clock retreat caused by a change in UT offset, 866.Ic zic 867produces a single transition to daylight saving at the new UT offset 868without any change in local (wall clock) time. 869To get separate transitions 870use multiple zone continuation lines 871specifying transition instants using universal time. 872.Sh SEE ALSO 873.Xr tzfile 5 , 874.Xr zdump 8 875