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na_zoneinfo - time zone information files
/etc/zoneinfo
The directory /etc/zoneinfo contains time zone information
files used by the timezone command (see na_timezone(1)).
They are in standard Unix time zone file format as
described below.
The time zone information files begin with bytes reserved
for future use, followed by six four-byte signed values,
written in a "standard" byte order (the high-order byte of
the value is written first). These values are, in order:
-
tzh_ttisgmtcnt
- The number of GMT/local indicators
stored in the file.
-
tzh_ttisstdcnt
- The number of standard/wall
indicators stored in the file.
-
tzh_leapcnt
- The number of leap seconds for
which data is stored in the
file.
-
tzh_timecnt
- The number of "transition
times" for which data is stored
in the file.
-
tzh_typecnt
- The number of "local time
types" for which data is stored
in the file (must not be zero).
-
tzh_charcnt
- The number of characters of
"time zone abbreviation
strings" stored in the file.
The above header is followed by tzh_timecnt four-byte
signed values, sorted in ascending order. These values
are written in "standard" byte order. Each is used as a
transition time at which the rules for computing local
time change. Next come tzh_timecnt one-byte unsigned values;
each one tells which of the different types of "local
time" types described in the file is associated with the
same-indexed transition time. These values serve as
indices into an array of structures that appears next in
the file; these structures are written as a four-byte
signed tt_gmtoff member in a standard byte order, followed
by a one-byte signed tt_isdst member and a one-byte
unsigned tt_abbrind member. In each structure, tt_gmtoff
gives the number of seconds to be added to GMT, tt_isdst
tells whether this time is during a Daylight Savings Time
period and tt_abbrind serves as an index into the array of
time zone abbreviation characters that follow the structure(s)
in the file.
Then there are tzh_leapcnt pairs of four-byte values,
written in standard byte order; the first value of each
pair gives the time at which a leap second occurs; the
second gives the total number of leap seconds to be
applied after the given time. The pairs of values are
sorted in ascending order by time.
Then there are tzh_ttisstdcnt standard/wall indicators,
each stored as a one-byte value; they tell whether the
transition times associated with local time types were
specified as standard time or wall clock time. A local
time transition specified in standard time ignores any
offset due to Daylight Savings Time. On the other hand, a
time specified in wall clock time takes the prevailing
value of Daylight Savings Time in to account.
Finally there are tzh_ttisgmtcnt GMT/local indicators,
each stored as a one-byte value; they tell whether the
transition times associated with local time types were
specified as GMT or local time.
na_timezone(1)
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