diff options
Diffstat (limited to 'man/man8/zic.8')
| -rw-r--r-- | man/man8/zic.8 | 894 |
1 files changed, 894 insertions, 0 deletions
diff --git a/man/man8/zic.8 b/man/man8/zic.8 new file mode 100644 index 000000000..0ad373a2d --- /dev/null +++ b/man/man8/zic.8 @@ -0,0 +1,894 @@ +.\" This file is in the public domain, so clarified as of +.\" 2009-05-17 by Arthur David Olson. +.TH zic 8 "" "Time Zone Database" +.SH NAME +zic \- timezone compiler +.SH SYNOPSIS +.B zic +[ +.I option +\&... ] [ +.I filename +\&... ] +.SH DESCRIPTION +.ie '\(lq'' .ds lq \&"\" +.el .ds lq \(lq\" +.ie '\(rq'' .ds rq \&"\" +.el .ds rq \(rq\" +.de q +\\$3\*(lq\\$1\*(rq\\$2 +.. +.ie '\(la'' .ds < < +.el .ds < \(la +.ie '\(ra'' .ds > > +.el .ds > \(ra +.ie \n(.g \{\ +. ds : \: +. ds - \f(CR-\fP +.\} +.el \{\ +. ds : +. ds - \- +.\} +.ds d " degrees +.ds m " minutes +.ds s " seconds +.ds _ " \& +.if t \{\ +. if \n(.g .if c \(de .if c \(fm .if c \(sd \{\ +. ds d \(de +. ds m \(fm +. ds s \(sd +. ds _ \| +. \} +.\} +The +.B zic +program reads text from the file(s) named on the command line +and creates the timezone information format (TZif) files +specified in this input. +If a +.I filename +is +.q "\*-" , +standard input is read. +.SH OPTIONS +.TP +.B "\*-\*-version" +Output version information and exit. +.TP +.B \*-\*-help +Output short usage message and exit. +.TP +.BI "\*-b " bloat +Output backward-compatibility data as specified by +.IR bloat . +If +.I bloat +is +.BR fat , +generate additional data entries that work around potential bugs or +incompatibilities in older software, such as software that mishandles +the 64-bit generated data. +If +.I bloat +is +.BR slim , +keep the output files small; this can help check for the bugs +and incompatibilities. +The default is +.BR slim , +as software that mishandles 64-bit data typically +mishandles timestamps after the year 2038 anyway. +Also see the +.B \*-r +option for another way to alter output size. +.TP +.BI "\*-d " directory +Create time conversion information files in the named directory rather than +in the standard directory named below. +.TP +.BI "\*-l " timezone +Use +.I timezone +as local time. +.B zic +will act as if the input contained a link line of the form +.sp +.ti +2 +.ta \w'Link\0\0'u +\w'\fItimezone\fP\0\0'u +Link \fItimezone\fP localtime +.sp +If +.I timezone +is +.BR \*- , +any already-existing link is removed. +.TP +.BI "\*-L " leapsecondfilename +Read leap second information from the file with the given name. +If this option is not used, +no leap second information appears in output files. +.TP +.BI "\*-p " timezone +Use +.IR timezone 's +rules when handling nonstandard +TZ strings like "EET\*-2EEST" that lack transition rules. +.B zic +will act as if the input contained a link line of the form +.sp +.ti +2 +Link \fItimezone\fP posixrules +.sp +If +.I timezone +is +.q "\*-" +(the default), any already-existing link is removed. +.sp +Unless +.I timezone is +.q "\*-" , +this option is obsolete and poorly supported. +Among other things it should not be used for timestamps after the year 2037, +and it should not be combined with +.B "\*-b slim" +if +.IR timezone 's +transitions are at standard time or Universal Time (UT) instead of local time. +.TP +.BR "\*-r " "[\fB@\fP\fIlo\fP][\fB/@\fP\fIhi\fP]" +Limit the applicability of output files +to timestamps in the range from +.I lo +(inclusive) to +.I hi +(exclusive), where +.I lo +and +.I hi +are possibly signed decimal counts of seconds since the Epoch +(1970-01-01 00:00:00 UTC). +Omitted counts default to extreme values. +The output files use UT offset 0 and abbreviation +.q "\*-00" +in place of the omitted timestamp data. +For example, +.q "zic \*-r @0" +omits data intended for negative timestamps (i.e., before the Epoch), and +.q "zic \*-r @0/@2147483648" +outputs data intended only for nonnegative timestamps that fit into +31-bit signed integers. +On platforms with GNU +.BR date , +.q "zic \*-r @$(date +%s)" +omits data intended for past timestamps. +Although this option typically reduces the output file's size, +the size can increase due to the need to represent the timestamp range +boundaries, particularly if +.I hi +causes a TZif file to contain explicit entries for +.RI pre- hi +transitions rather than concisely representing them +with an extended POSIX.1-2017 TZ string. +Also see the +.B "\*-b slim" +option for another way to shrink output size. +.TP +.BI "\*-R @" hi +Generate redundant trailing explicit transitions for timestamps +that occur less than +.I hi +seconds since the Epoch, even though the transitions could be +more concisely represented via the extended POSIX.1-2017 TZ string. +This option does not affect the represented timestamps. +Although it accommodates nonstandard TZif readers +that ignore the extended POSIX.1-2017 TZ string, +it increases the size of the altered output files. +.TP +.BI "\*-t " file +When creating local time information, put the configuration link in +the named file rather than in the standard location. +.TP +.B \*-v +Be more verbose, and complain about the following situations: +.RS +.PP +The input specifies a link to a link, +something not supported by some older parsers, including +.B zic +itself through release 2022e. +.PP +A year that appears in a data file is outside the range +of representable years. +.PP +A time of 24:00 or more appears in the input. +Pre-1998 versions of +.B zic +prohibit 24:00, and pre-2007 versions prohibit times greater than 24:00. +.PP +A rule goes past the start or end of the month. +Pre-2004 versions of +.B zic +prohibit this. +.PP +A time zone abbreviation uses a +.B %z +format. +Pre-2015 versions of +.B zic +do not support this. +.PP +A timestamp contains fractional seconds. +Pre-2018 versions of +.B zic +do not support this. +.PP +The input contains abbreviations that are mishandled by pre-2018 versions of +.B zic +due to a longstanding coding bug. +These abbreviations include +.q L +for +.q Link , +.q mi +for +.q min , +.q Sa +for +.q Sat , +and +.q Su +for +.q Sun . +.PP +The output file does not contain all the information about the +long-term future of a timezone, because the future cannot be summarized as +an extended POSIX.1-2017 TZ string. For example, as of 2023 this problem +occurs for Morocco's daylight-saving rules, as these rules are based +on predictions for when Ramadan will be observed, something that +an extended POSIX.1-2017 TZ string cannot represent. +.PP +The output contains data that may not be handled properly by client +code designed for older +.B zic +output formats. These compatibility issues affect only timestamps +before 1970 or after the start of 2038. +.PP +The output contains a truncated leap second table, +which can cause some older TZif readers to misbehave. +This can occur if the +.B "\*-L" +option is used, and either an Expires line is present or +the +.B "\*-r" +option is also used. +.PP +The output file contains more than 1200 transitions, +which may be mishandled by some clients. +The current reference client supports at most 2000 transitions; +pre-2014 versions of the reference client support at most 1200 +transitions. +.PP +A time zone abbreviation has fewer than 3 or more than 6 characters. +POSIX requires at least 3, and requires implementations to support +at least 6. +.PP +An output file name contains a byte that is not an ASCII letter, +.q "\*-" , +.q "/" , +or +.q "_" ; +or it contains a file name component that contains more than 14 bytes +or that starts with +.q "\*-" . +.RE +.SH FILES +Input files use the format described in this section; output files use +.BR tzfile (5) +format. +.PP +Input files should be text files, that is, they should be a series of +zero or more lines, each ending in a newline byte and containing at +most 2048 bytes counting the newline, and without any NUL bytes. +The input text's encoding +is typically UTF-8 or ASCII; it should have a unibyte representation +for the POSIX Portable Character Set (PPCS) +\*<https://pubs\*:.opengroup\*:.org/\*:onlinepubs/\*:9699919799/\*:basedefs/\*:V1_chap06\*:.html\*> +and the encoding's non-unibyte characters should consist entirely of +non-PPCS bytes. Non-PPCS characters typically occur only in comments: +although output file names and time zone abbreviations can contain +nearly any character, other software will work better if these are +limited to the restricted syntax described under the +.B \*-v +option. +.PP +Input lines are made up of fields. +Fields are separated from one another by one or more white space characters. +The white space characters are space, form feed, carriage return, newline, +tab, and vertical tab. +Leading and trailing white space on input lines is ignored. +An unquoted sharp character (#) in the input introduces a comment which extends +to the end of the line the sharp character appears on. +White space characters and sharp characters may be enclosed in double quotes +(") if they're to be used as part of a field. +Any line that is blank (after comment stripping) is ignored. +Nonblank lines are expected to be of one of three types: +rule lines, zone lines, and link lines. +.PP +Names must be in English and are case insensitive. +They appear in several contexts, and include month and weekday names +and keywords such as +.BR "maximum" , +.BR "only" , +.BR "Rolling" , +and +.BR "Zone" . +A name can be abbreviated by omitting all but an initial prefix; any +abbreviation must be unambiguous in context. +.PP +A rule line has the form +.nf +.ti +2 +.ta \w'Rule\0\0'u +\w'NAME\0\0'u +\w'FROM\0\0'u +\w'1973\0\0'u +\w'\*-\0\0'u +\w'Apr\0\0'u +\w'lastSun\0\0'u +\w'2:00w\0\0'u +\w'1:00d\0\0'u +.sp +Rule NAME FROM TO \*- IN ON AT SAVE LETTER/S +.sp +For example: +.ti +2 +.sp +Rule US 1967 1973 \*- Apr lastSun 2:00w 1:00d D +.sp +.fi +The fields that make up a rule line are: +.TP +.B NAME +Gives the name of the rule set that contains this line. +The name must start with a character that is neither +an ASCII digit nor +.q \*- +nor +.q + . +To allow for future extensions, +an unquoted name should not contain characters from the set +.ie \n(.g .q \f(CR!$%&\(aq()*,/:;<=>?@[\e]\(ha\(ga{|}\(ti\fP . +.el .ie t .q \f(CW!$%&'()*,/:;<=>?@[\e]^\(ga{|}~\fP . +.el .q !$%&'()*,/:;<=>?@[\e]^`{|}~ . +.TP +.B FROM +Gives the first year in which the rule applies. +Any signed integer year can be supplied; the proleptic Gregorian calendar +is assumed, with year 0 preceding year 1. +Rules can describe times that are not representable as time values, +with the unrepresentable times ignored; this allows rules to be portable +among hosts with differing time value types. +.TP +.B TO +Gives the final year in which the rule applies. +The word +.B maximum +(or an abbreviation) means the indefinite future, and the word +.B only +(or an abbreviation) +may be used to repeat the value of the +.B FROM +field. +.TP +.B \*- +Is a reserved field and should always contain +.q \*- +for compatibility with older versions of +.BR zic . +It was previously known as the +.B TYPE +field, which could contain values to allow a +separate script to further restrict in which +.q types +of years the rule would apply. +.TP +.B IN +Names the month in which the rule takes effect. +Month names may be abbreviated. +.TP +.B ON +Gives the day on which the rule takes effect. +Recognized forms include: +.nf +.in +2 +.sp +.ta \w'Sun<=25\0\0'u +5 the fifth of the month +lastSun the last Sunday in the month +lastMon the last Monday in the month +Sun>=8 first Sunday on or after the eighth +Sun<=25 last Sunday on or before the 25th +.fi +.in +.sp +A weekday name (e.g., +.BR "Sunday" ) +or a weekday name preceded by +.q "last" +(e.g., +.BR "lastSunday" ) +may be abbreviated or spelled out in full. +There must be no white space characters within the +.B ON +field. +The +.q <= +and +.q >= +constructs can result in a day in the neighboring month; +for example, the IN-ON combination +.q "Oct Sun>=31" +stands for the first Sunday on or after October 31, +even if that Sunday occurs in November. +.TP +.B AT +Gives the time of day at which the rule takes effect, +relative to 00:00, the start of a calendar day. +Recognized forms include: +.nf +.in +2 +.sp +.ta \w'00:19:32.13\0\0'u +2 time in hours +2:00 time in hours and minutes +01:28:14 time in hours, minutes, and seconds +00:19:32.13 time with fractional seconds +12:00 midday, 12 hours after 00:00 +15:00 3 PM, 15 hours after 00:00 +24:00 end of day, 24 hours after 00:00 +260:00 260 hours after 00:00 +\*-2:30 2.5 hours before 00:00 +\*- equivalent to 0 +.fi +.in +.sp +Although +.B zic +rounds times to the nearest integer second +(breaking ties to the even integer), the fractions may be useful +to other applications requiring greater precision. +The source format does not specify any maximum precision. +Any of these forms may be followed by the letter +.B w +if the given time is local or +.q "wall clock" +time, +.B s +if the given time is standard time without any adjustment for daylight saving, +or +.B u +(or +.B g +or +.BR z ) +if the given time is universal time; +in the absence of an indicator, +local (wall clock) time is assumed. +These forms ignore leap seconds; for example, +if a leap second occurs at 00:59:60 local time, +.q "1:00" +stands for 3601 seconds after local midnight instead of the usual 3600 seconds. +The intent is that a rule line describes the instants when a +clock/calendar set to the type of time specified in the +.B AT +field would show the specified date and time of day. +.TP +.B SAVE +Gives the amount of time to be added to local standard time when the rule is in +effect, and whether the resulting time is standard or daylight saving. +This field has the same format as the +.B AT +field +except with a different set of suffix letters: +.B s +for standard time and +.B d +for daylight saving time. +The suffix letter is typically omitted, and defaults to +.B s +if the offset is zero and to +.B d +otherwise. +Negative offsets are allowed; in Ireland, for example, daylight saving +time is observed in winter and has a negative offset relative to +Irish Standard Time. +The offset is merely added to standard time; for example, +.B zic +does not distinguish a 10:30 standard time plus an 0:30 +.B SAVE +from a 10:00 standard time plus a 1:00 +.BR SAVE . +.TP +.B LETTER/S +Gives the +.q "variable part" +(for example, the +.q "S" +or +.q "D" +in +.q "EST" +or +.q "EDT" ) +of time zone abbreviations to be used when this rule is in effect. +If this field is +.q \*- , +the variable part is null. +.PP +A zone line has the form +.sp +.nf +.ti +2 +.ta \w'Zone\0\0'u +\w'Asia/Amman\0\0'u +\w'STDOFF\0\0'u +\w'Jordan\0\0'u +\w'FORMAT\0\0'u +Zone NAME STDOFF RULES FORMAT [UNTIL] +.sp +For example: +.sp +.ti +2 +Zone Asia/Amman 2:00 Jordan EE%sT 2017 Oct 27 01:00 +.sp +.fi +The fields that make up a zone line are: +.TP +.B NAME +The name of the timezone. +This is the name used in creating the time conversion information file for the +timezone. +It should not contain a file name component +.q ".\&" +or +.q ".." ; +a file name component is a maximal substring that does not contain +.q "/" . +.TP +.B STDOFF +The amount of time to add to UT to get standard time, +without any adjustment for daylight saving. +This field has the same format as the +.B AT +and +.B SAVE +fields of rule lines, except without suffix letters; +begin the field with a minus sign if time must be subtracted from UT. +.TP +.B RULES +The name of the rules that apply in the timezone or, +alternatively, a field in the same format as a rule-line SAVE column, +giving the amount of time to be added to local standard time +and whether the resulting time is standard or daylight saving. +If this field is +.B \*- +then standard time always applies. +When an amount of time is given, only the sum of standard time and +this amount matters. +.TP +.B FORMAT +The format for time zone abbreviations. +The pair of characters +.B %s +is used to show where the +.q "variable part" +of the time zone abbreviation goes. +Alternatively, a format can use the pair of characters +.B %z +to stand for the UT offset in the form +.RI \(+- hh , +.RI \(+- hhmm , +or +.RI \(+- hhmmss , +using the shortest form that does not lose information, where +.IR hh , +.IR mm , +and +.I ss +are the hours, minutes, and seconds east (+) or west (\-) of UT. +Alternatively, +a slash (/) +separates standard and daylight abbreviations. +To conform to POSIX, a time zone abbreviation should contain only +alphanumeric ASCII characters, +.q "+" +and +.q "\*-". +By convention, the time zone abbreviation +.q "\*-00" +is a placeholder that means local time is unspecified. +.TP +.B UNTIL +The time at which the UT offset or the rule(s) change for a location. +It takes the form of one to four fields YEAR [MONTH [DAY [TIME]]]. +If this is specified, +the time zone information is generated from the given UT offset +and rule change until the time specified, which is interpreted using +the rules in effect just before the transition. +The month, day, and time of day have the same format as the IN, ON, and AT +fields of a rule; trailing fields can be omitted, and default to the +earliest possible value for the missing fields. +.IP +The next line must be a +.q "continuation" +line; this has the same form as a zone line except that the +string +.q "Zone" +and the name are omitted, as the continuation line will +place information starting at the time specified as the +.q "until" +information in the previous line in the file used by the previous line. +Continuation lines may contain +.q "until" +information, just as zone lines do, indicating that the next line is a further +continuation. +.PP +If a zone changes at the same instant that a rule would otherwise take +effect in the earlier zone or continuation line, the rule is ignored. +A zone or continuation line +.I L +with a named rule set starts with standard time by default: +that is, any of +.IR L 's +timestamps preceding +.IR L 's +earliest rule use the rule in effect after +.IR L 's +first transition into standard time. +In a single zone it is an error if two rules take effect at the same +instant, or if two zone changes take effect at the same instant. +.PP +If a continuation line subtracts +.I N +seconds from the UT offset after a transition that would be +interpreted to be later if using the continuation line's UT offset and +rules, the +.q "until" +time of the previous zone or continuation line is interpreted +according to the continuation line's UT offset and rules, and any rule +that would otherwise take effect in the next +.I N +seconds is instead assumed to take effect simultaneously. +For example: +.br +.ne 7 +.nf +.in +2 +.ta \w'# Rule\0\0'u +\w'NAME\0\0'u +\w'FROM\0\0'u +\w'2006\0\0'u +\w'\*-\0\0'u +\w'Oct\0\0'u +\w'lastSun\0\0'u +\w'2:00\0\0'u +\w'SAVE\0\0'u +.sp +# Rule NAME FROM TO \*- IN ON AT SAVE LETTER/S +Rule US 1967 2006 - Oct lastSun 2:00 0 S +Rule US 1967 1973 - Apr lastSun 2:00 1:00 D +.ta \w'# Zone\0\0'u +\w'America/Menominee\0\0'u +\w'STDOFF\0\0'u +\w'RULES\0\0'u +\w'FORMAT\0\0'u +# Zone NAME STDOFF RULES FORMAT [UNTIL] +Zone America/Menominee \*-5:00 \*- EST 1973 Apr 29 2:00 + \*-6:00 US C%sT +.sp +.in +.fi +Here, an incorrect reading would be there were two clock changes on 1973-04-29, +the first from 02:00 EST (\*-05) to 01:00 CST (\*-06), +and the second an hour later from 02:00 CST (\*-06) to 03:00 CDT (\*-05). +However, +.B zic +interprets this more sensibly as a single transition from 02:00 CST (\*-05) to +02:00 CDT (\*-05). +.PP +A link line has the form +.sp +.nf +.ti +2 +.ta \w'Link\0\0'u +\w'Europe/Istanbul\0\0'u +Link TARGET LINK-NAME +.sp +For example: +.sp +.ti +2 +Link Europe/Istanbul Asia/Istanbul +.sp +.fi +The +.B TARGET +field should appear as the +.B NAME +field in some zone line or as the +.B LINK-NAME +field in some link line. +The +.B LINK-NAME +field is used as an alternative name for that zone; +it has the same syntax as a zone line's +.B NAME +field. +Links can chain together, although the behavior is unspecified if a +chain of one or more links does not terminate in a Zone name. +A link line can appear before the line that defines the link target. +For example: +.sp +.ne 3 +.nf +.in +2 +.ta \w'Zone\0\0'u +\w'Greenwich\0\0'u +Link Greenwich G_M_T +Link Etc/GMT Greenwich +Zone Etc/GMT\0\00\0\0\*-\0\0GMT +.sp +.in +.fi +The two links are chained together, and G_M_T, Greenwich, and Etc/GMT +all name the same zone. +.PP +Except for continuation lines, +lines may appear in any order in the input. +However, the behavior is unspecified if multiple zone or link lines +define the same name. +.PP +The file that describes leap seconds can have leap lines and an +expiration line. +Leap lines have the following form: +.nf +.ti +2 +.ta \w'Leap\0\0'u +\w'YEAR\0\0'u +\w'MONTH\0\0'u +\w'DAY\0\0'u +\w'HH:MM:SS\0\0'u +\w'CORR\0\0'u +.sp +Leap YEAR MONTH DAY HH:MM:SS CORR R/S +.sp +For example: +.ti +2 +.sp +Leap 2016 Dec 31 23:59:60 + S +.sp +.fi +The +.BR YEAR , +.BR MONTH , +.BR DAY , +and +.B HH:MM:SS +fields tell when the leap second happened. +The +.B CORR +field +should be +.q "+" +if a second was added +or +.q "\*-" +if a second was skipped. +The +.B R/S +field +should be (an abbreviation of) +.q "Stationary" +if the leap second time given by the other fields should be interpreted as UTC +or +(an abbreviation of) +.q "Rolling" +if the leap second time given by the other fields should be interpreted as +local (wall clock) time. +.PP +Rolling leap seconds were implemented back when it was not +clear whether common practice was rolling or stationary, +with concerns that one would see +Times Square ball drops where there'd be a +.q "3... 2... 1... leap... Happy New Year" +countdown, placing the leap second at +midnight New York time rather than midnight UTC. +However, this countdown style does not seem to have caught on, +which means rolling leap seconds are not used in practice; +also, they are not supported if the +.B \*-r +option is used. +.PP +The expiration line, if present, has the form: +.nf +.ti +2 +.ta \w'Expires\0\0'u +\w'YEAR\0\0'u +\w'MONTH\0\0'u +\w'DAY\0\0'u +.sp +Expires YEAR MONTH DAY HH:MM:SS +.sp +For example: +.ti +2 +.sp +Expires 2020 Dec 28 00:00:00 +.sp +.fi +The +.BR YEAR , +.BR MONTH , +.BR DAY , +and +.B HH:MM:SS +fields give the expiration timestamp in UTC for the leap second table. +.br +.ne 22 +.SH "EXTENDED EXAMPLE" +Here is an extended example of +.B zic +input, intended to illustrate many of its features. +.nf +.in +2 +.ta \w'# Rule\0\0'u +\w'NAME\0\0'u +\w'FROM\0\0'u +\w'1973\0\0'u +\w'\*-\0\0'u +\w'Apr\0\0'u +\w'lastSun\0\0'u +\w'2:00\0\0'u +\w'SAVE\0\0'u +.sp +# Rule NAME FROM TO \*- IN ON AT SAVE LETTER/S +Rule Swiss 1941 1942 \*- May Mon>=1 1:00 1:00 S +Rule Swiss 1941 1942 \*- Oct Mon>=1 2:00 0 \*- +.sp .5 +Rule EU 1977 1980 \*- Apr Sun>=1 1:00u 1:00 S +Rule EU 1977 only \*- Sep lastSun 1:00u 0 \*- +Rule EU 1978 only \*- Oct 1 1:00u 0 \*- +Rule EU 1979 1995 \*- Sep lastSun 1:00u 0 \*- +Rule EU 1981 max \*- Mar lastSun 1:00u 1:00 S +Rule EU 1996 max \*- Oct lastSun 1:00u 0 \*- +.sp +.ta \w'# Zone\0\0'u +\w'Europe/Zurich\0\0'u +\w'0:29:45.50\0\0'u +\w'RULES\0\0'u +\w'FORMAT\0\0'u +# Zone NAME STDOFF RULES FORMAT [UNTIL] +Zone Europe/Zurich 0:34:08 \*- LMT 1853 Jul 16 + 0:29:45.50 \*- BMT 1894 Jun + 1:00 Swiss CE%sT 1981 + 1:00 EU CE%sT +.sp +Link Europe/Zurich Europe/Vaduz +.sp +.in +.fi +In this example, the EU rules are for the European Union +and for its predecessor organization, the European Communities. +The timezone is named Europe/Zurich and it has the alias Europe/Vaduz. +This example says that Zurich was 34 minutes and 8 +seconds east of UT until 1853-07-16 at 00:00, when the legal offset +was changed to +7\*d\*_26\*m\*_22.50\*s, +which works out to 0:29:45.50; +.B zic +treats this by rounding it to 0:29:46. +After 1894-06-01 at 00:00 the UT offset became one hour +and Swiss daylight saving rules (defined with lines beginning with +.q "Rule Swiss") +apply. From 1981 to the present, EU daylight saving rules have +applied, and the UTC offset has remained at one hour. +.PP +In 1941 and 1942, daylight saving time applied from the first Monday +in May at 01:00 to the first Monday in October at 02:00. +The pre-1981 EU daylight-saving rules have no effect +here, but are included for completeness. Since 1981, daylight +saving has begun on the last Sunday in March at 01:00 UTC. +Until 1995 it ended the last Sunday in September at 01:00 UTC, +but this changed to the last Sunday in October starting in 1996. +.PP +For purposes of display, +.q "LMT" +and +.q "BMT" +were initially used, respectively. Since +Swiss rules and later EU rules were applied, the time zone abbreviation +has been CET for standard time and CEST for daylight saving +time. +.SH FILES +.TP +.I /etc/localtime +Default local timezone file. +.TP +.I /usr/share/zoneinfo +Default timezone information directory. +.SH NOTES +For areas with more than two types of local time, +you may need to use local standard time in the +.B AT +field of the earliest transition time's rule to ensure that +the earliest transition time recorded in the compiled file is correct. +.PP +If, +for a particular timezone, +a clock advance caused by the start of daylight saving +coincides with and is equal to +a clock retreat caused by a change in UT offset, +.B zic +produces a single transition to daylight saving at the new UT offset +without any change in local (wall clock) time. +To get separate transitions +use multiple zone continuation lines +specifying transition instants using universal time. +.SH SEE ALSO +.BR tzfile (5), +.BR zdump (8) |