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13
The TIMEZONE_TZ Setting
The value of the TZ environment variable should be set as follows (spaces are for clarity only):
std offset dst offset, rule
The expanded format is as follows:
stdoffset[dst[offset][,start[/time],end[/time]]]
where
std , dst
Three or more letters that you specify to designate the standard (std) or summer (dst) time zone. Only std is
required. If dst is omitted, then summer time doesn’t apply in this locale. Upper- and lowercase letters are
allowed. Any characters except for a leading colon (:), digits, comma (,), minus (-), plus (+), and ASCII NUL
(\0) are allowed.
There is no specified list of time zone designations, you can specify whatever name or acronym you’d like. What’s
important is the information that follows the names — the numbers that indicate the difference between the local
time and UTC, and the rules that specify when to switch on, or out of, daylight saving time.
offset Indicates the value one must add to the local time to arrive at Coordinated Universal Time (UTC). The offset
has the form:
hh [: mm [: ss ]]
Minutes ( mm ) and seconds ( ss ) are optional. The hour ( hh ) is required; it may be a single digit.
The offset following std is required. If no offset follows dst , summer time is assumed to be one hour ahead of
standard time.
One or more digits may be used; the value is always interpreted as a decimal number. The hour may be between 0
and 24; the minutes (and seconds), if present, between 0 and 59. If preceded by a “
-
”, the time zone is east of the
Prime Meridian ; otherwise it’s west (which may be indicated by an optional preceding “+”).
rule
Indicates when to change to and back from summer time. The rule has the form:
date / time , date / time
where the first date describes when the change from standard to summer time occurs, and the second date
describes when the change back happens. Each time field describes when, in current local time, the change to
the other time is made.
The format of
date may be one of the following:
J n
The Julian day n (1 <= n <= 365). Leap days aren’t counted. That is, in all years — including leap years —
February 28 is day 59 and March 1 is day 60. It’s impossible to refer explicitly to the occasional February 29.
n
The zero-based Julian day (0 <= n <= 365). Leap years are counted; it’s possible to refer to February 29.
M m.n.d
The d th day (0 <= d <= 6) of week n of month m of the year (1 <= n <= 5, 1 <= m <= 12, where week 5
means “the last d day in month m ”, which may occur in the fourth or fifth week). Week 1 is the first week in
which the d th day occurs. Day zero is Sunday.
The time has the same format as offset , except that no leading sign (“+” or “-”) is allowed. The default, if time is
omitted, is 02:00:00.
Here are some examples of TIMEZONE_TZ settings (Note - the “TZ=” is not required in ComCam):
TZ=EST5EDT
This is the default when the TZ variable isn’t set.
•
Eastern Standard Time is 5 hours earlier than Coordinated Universal Time (UTC). Standard
time and daylight saving time both apply to this locale.
•
By default, Eastern Daylight Time (EDT) is one hour ahead of standard time (that is,
EDT4).
•
Since it isn’t specified, daylight saving time starts on the first Sunday of April at 2:00 A.M.
and ends on the last Sunday of October at 2:00 A.M.