NAME
zic —
time zone compiler
SYNOPSIS
zic |
[--version]
[-d
directory]
[-L
leapsecondfilename]
[-l
localtime]
[-p
posixrules]
[-s]
[-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.
- -v
- Be more verbose, and complain about the following
situations:
- Pre-1998 versions of
zic(8) prohibit 24:00, and
pre-2007 versions prohibit times greater than 24:00.
- Pre-2004 versions of
zic(8) prohibit this.
- 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.
- code designed for older
zic(8) output formats.
These compatibility issues affect only time stamps before 1970 or
after the start of 2038.
- POSIX requires at least 3.
- “-”, “/”, 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 (such as month names) must be in English and are case insensitive.
Abbreviations, if used, 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
integer year can be supplied; the proleptic Gregorian calendar is
assumed. The word minimum (or an abbreviation) means
the minimum year representable as an integer. The word
maximum (or an abbreviation) means the maximum year
representable as an integer. 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.
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
- 15:00
- 24-hour format time (for times after noon)
- 1:28:14
- time in hours, minutes, and seconds
- -
- 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
w and s suffixes are not used).
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 [UNTILYEAR
[MONTH [DAY [TIME]]]]
For example:
Zone Australia/Adelaide 9:30 Aus AC%sT 1971
Oct 31 2:00
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/SAVE
- The name of the rule(s) 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 UTC 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 UTC. Alternatively, a slash (/) separates
standard and daylight abbreviations. To conform to POSIX, a time zone
abbreviation should contain only alphanumeric ASCII characters,
"+" and "".
- UNTILYEAR [MONTH [DAY
[TIME]]]
- The time at which the UT offset or the rule(s) change
for a location. It is specified as a year, a month, a day, and a time
of day. 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 1974 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.
# 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 |
Switzerland |
In this example, the zone is named Europe/Zurich but it has an alias as
Switzerland. This example says that Zurich was 34 minutes and 8 seconds west
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 Swiss daylight saving rules (defined with lines beginning
with "Rule Swiss") apply, and the UT offset became one hour. From
1981 to the present, EU daylight saving rules have applied, and the UTC offset
has remained at one hour.
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
/usr/share/zoneinfo - standard directory used for created
files
SEE ALSO
ctime(3),
tzfile(5),
zdump(8)