NAME
zic —
time zone compiler
SYNOPSIS
zic |
[--version]
[-d
directory]
[-L
leapsecondfilename]
[-l
localtime]
[-p
posixrules]
[-s]
[-t file]
[-v]
[-y
command]
[Filename ...] |
DESCRIPTION
zic reads text from the file(s) named on the command line and
creates the time conversion information files specified in this input. If a
filename is
-, the standard input
is read.
These options are available:
- --version
- Output version information and exit.
- -d
directory
- Create time conversion information files in the named
directory rather than in the standard directory named below.
- -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.
- -l
timezone
- Use the given time zone as local time.
zic will act as if the input contained a link line of
the form
Link timezone localtime
- -p
timezone
- Use the given time zone's rules when handling POSIX-format
time zone environment variables. zic will act as if the
input contained a link line of the form
Link timezone posixrules
- -s
- Limit time values stored in output files to values that are
the same whether they're taken to be signed or unsigned. You can use this
option to generate SVVS-compatible files.
- -t
file
- When creating local time information, put the configuration
link in the named file rather than in the standard location.
- -v
- Be more verbose, and complain about the following
situations:
- The input specifies a link to a link.
- A year that appears in a data file is outside the
range of years representable by
time(2) values.
- A time of 24:00 or more appears in the input. Pre-1998
versions of zic(8) prohibit
24:00, and pre-2007 versions prohibit times greater than 24:00.
- A rule goes past the start or end of the month.
Pre-2004 versions of zic(8)
prohibit this.
- The output file does not contain all the information
about the long-term future of a zone, because the future cannot be
summarized as an extended POSIX TZ string. For example, as of 2013
this problem occurs for Iran's daylight-saving rules for the predicted
future, as these rules are based on the Iranian calendar, which cannot
be represented.
- The output contains data that may not be handled
properly by client code designed for older
zic(8) output formats.
These compatibility issues affect only time stamps before 1970 or
after the start of 2038.
- A time zone abbreviation has fewer than 3 characters.
POSIX requires at least 3.
- An output file name contains a byte that is not an
ASCII letter, “-”, “/”, or “_”; or
it or it contains a file name component that contains more than 14
bytes or that starts with “-”.
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 511 bytes,
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)
http://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 [
v] option.
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. Non-blank lines
are expected to be of one of three types: rule lines, zone lines, and link
lines.
Names must be in English and are case insensitive. They appear in several
contexts, and include month and weekday names and keywords such as
“maximum”, “only”, “Rolling”, and
“Zone”. A name can be abbreviated by omitting all but an initial
prefix; any abbreviation must be unambiguous in context.
A rule line has the form
Rule NAME FROM TO TYPE IN ON AT SAVE LETTER/S
For example:
Rule US 1967 1973 - Apr lastSun 2:00 1:00 D
The fields that make up a rule line are:
-
-
- NAME
- Gives the (arbitrary) name of the set of rules this rule is
part of.
-
-
- 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. The word minimum (or an
abbreviation) means the indefinite past. The word
maximum (or an abbreviation) means the indefinite
future. 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.
-
-
- TO
- Gives the final year in which the rule applies. In addition
to minimum and maximum (as above), the
word only (or an abbreviation) may be used to repeat the
value of the FROM field.
-
-
- TYPE
- should be “-” and is present for compatibility
with older versions of zic in which it could contain
year types.
-
-
- IN
- Names the month in which the rule takes effect. Month names
may be abbreviated.
-
-
- ON
- Gives the day on which the rule takes effect. Recognized
forms include:
- 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
Names of days of the week may be abbreviated or spelled out in full. A
weekday name (e.g., “Sunday”) or a weekday name preceded by
“last” (e.g., “lastSunday”) may be abbreviated or
spelled out in full. Note that there must be no spaces within the
ON field.
-
-
- AT
- Gives the time of day at which the rule takes effect.
Recognized forms include:
- 2
- time in hours
- 2:00
- time in hours and minutes
- 01:28:14
- time in hours, minutes, and seconds
- 15:00
- 24-hour format time (for times after noon)
- 260:00
- 260 hours after 00:00
- -2:30
- 2.5 hours before 00:00
- -
- equivalent to 0
where hour 0 is midnight at the start of the day, and hour 24 is midnight at
the end of the day. Any of these forms may be followed by the letter
w if the given time is local “wall clock”
time, s if the given time is local
“standard” time, or u (or
g or z) if the given time is universal
time; in the absence of an indicator, wall clock time is assumed. The
intent is that a rule line describes the instants when a clock/calendar
set to the type of time specified in the AT field would
show the specified date and time of day.
-
-
- SAVE
- Gives the amount of time to be added to local standard time
when the rule is in effect. This field has the same format as the
AT field (although, of course, the suffixes are not
used). 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. Only the sum of standard time and this amount
matters; for example, zic does not distinguish a 10:30
standard time plus an 0:30 SAVE from a 10:00 standard
time plus a 1:00 SAVE.
-
-
- LETTER/S
- Gives the “variable part” (for example, the
“S” or “D” in “EST” or
“EDT”) of time zone abbreviations to be used when this rule is
in effect. If this field is -, the variable part is
null.
A zone line has the form
Zone NAME GMTOFF RULES/SAVE FORMAT [UNTIL]
For example:
Zone Asia/Amman 2:00 Jordan EE%sT 2017 Oct 27
1:00
The fields that make up a zone line are:
-
-
- NAME
- The name of the time zone. This is the name used in
creating the time conversion information file for the zone. It should not
contain a file name component “”. or “..”; a file
name component is a maximal substring that does not contain
“/”.
-
-
- GMTOFF
- The amount of time to add to UT to get standard time in
this zone. This field has the same format as the AT and
SAVE fields of rule lines; begin the field with a minus
sign if time must be subtracted from UT.
-
-
- RULES
- The name of the rules that apply in the time zone or,
alternatively, an amount of time to add to local standard time. If this
field is - then standard time always applies in the time
zone. When an amount of time is given, only the sum of standard time and
this amount matters.
-
-
- FORMAT
- The format for time zone abbreviations in this time zone.
The pair of characters %s is used to show where the
“variable part” of the time zone abbreviation goes.
Alternately, a format can use the pair of characters %z
+to stand for the UT offset in the form ± hh,
± hhmm, or ± hhmmss, using
the shortest form that does not lose information, where
hh, mm, and 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, "+" and "".
-
-
- UNTIL
- The time at which the UT offset or the rule(s) change for a
location. It takes the form of 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.
The next line must be a “continuation” line; this has the same
form as a zone line except that the string “Zone” and the name
are omitted, as the continuation line will place information starting at
the time specified as the until information in the
previous line in the file used by the previous line. Continuation lines
may contain until information, just as zone lines do,
indicating that the next line is a further continuation.
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. 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.
A link line has the form
Link TARGET LINK-NAME
For example:
Link Europe/Istanbul Asia/Istanbul
The
TARGET field should appear as the
NAME
field in some zone line. The
LINK-NAME field is used as an
alternative name for that zone; it has the same syntax as a zone line's
NAME field.
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, or if the source of one link line is the target of another.
Lines in the file that describes leap seconds have the following form:
Leap YEAR MONTH DAY HH:MM:SS CORR R/S
For example:
Leap 2016 Dec 31 23:59:60 + S
The
YEAR,
MONTH,
DAY, and
HH:MM:SS fields tell when the leap second happened. The
CORR field should be “+” if a second was added
or “-” if a second was skipped. The
R/S field
should be (an abbreviation of) “Stationary” if the leap second
time given by the other fields should be interpreted as UTC or (an
abbreviation of) “Rolling” if the leap second time given by the
other fields should be interpreted as local wall clock time.
EXTENDED EXAMPLE
Here is an extended example of
zic input, intended to
illustrate many of its features. In this example, the EU rules are for the
European Union and for its predecessor organization, the European Communities.
# Rule |
NAME |
FROM |
TO |
TYPE |
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 |
-
|
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 |
- |
# Zone |
NAME |
GMTOFF |
RULES/SAVE |
FORMAT |
[UNTIL] |
Zone |
Europe/Zurich |
0:34:08 |
- |
LMT |
1853 Jul 16 |
|
|
0:29:44 |
- |
BMT |
1894 Jun |
|
|
1:00 |
Swiss |
CE%sT |
1981 |
|
|
1:00 |
EU |
CE%sT |
Link |
Europe/Zurich |
Europe/Vaduz |
In this example, the zone is named Europe/Zurich but it has an alias as
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°26′22.50″; although this works out to 0:29:45.50, the input
format cannot represent fractional seconds so it is rounded here. After
1894-06-01 at 00:00 the UT offset became one hour and Swiss daylight saving
rules (defined with lines beginning with "Rule Swiss") apply. From
1981 to the present, EU daylight saving rules have
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.
For purposes of display, "LMT" and "BMT" were initially
used, respectively. Since Swiss rules and later EU rules were applied, the
display name for the time zone has been CET for standard time and CEST for
daylight saving time.
NOTES
For areas with more than two types of local time, you may need to use local
standard time in the
AT field of the earliest transition
time's rule to ensure that the earliest transition time recorded in the
compiled file is correct.
If, for a particular zone, 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,
zic produces a single transition to daylight saving
at the new UT offset (without any change in wall clock time). To get separate
transitions use multiple zone continuation lines specifying transition
instants using universal time.
Time stamps well before the Big Bang are silently omitted from the output. This
works around bugs in software that mishandles large negative time stamps. Call
it sour grapes, but pre-Big-Bang time stamps are physically suspect anyway.
The pre-Big-Bang cutoff time is approximate and may change in future versions.
FILES
- /etc/localtime
- default local time zone file
- /usr/share/zoneinfo
- standard directory used for created files
SEE ALSO
ctime(3),
tzfile(5),
zdump(8)