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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 signed 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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