void
tzset(
void
)
)
function uses the value of the environment variable
TZ
to set time conversion information used by
localtime(3).
If
TZ
does not appear in the environment,
the best available approximation to local wall clock time, as
specified by the
tzfile(5)
format file
/etc/localtime
is used by
localtime(3).
If
TZ
appears in the environment but its value is a null string,
Coordinated Universal Time (UTC) is used (without leap second
correction).
If
TZ
appears in the environment and its value is not a null string:
When
TZ
is used as a pathname, if it begins with a slash, it is used as an
absolute pathname; otherwise, it is used as a pathname relative to
/usr/share/zoneinfo
.
The file must be in the format specified in
tzfile(5).
When
TZ
is used directly as a specification of the time conversion information,
it must have the following syntax (spaces inserted for clarity):
[offset ]
,rule[[std offset dst ]]
where:
[:mm
:ss[hh ]]
The minutes (mm) and seconds (ss) are optional. The hour (hh) is required and 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 must be between zero and 24, and the minutes (and seconds) -- if present -- between zero and 59. If preceded by a ``-'' the time zone shall be east of the Prime Meridian; otherwise it shall be west (which may be indicated by an optional preceding ``+'').
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.
date
is one of the following:
TZ
,
the rules specified by the
tzfile(5)
format file
posixrules
in
/usr/share/zoneinfo
are used, with the standard and summer time offsets from UTC replaced
by those specified by the
offset
values in
TZ
.
For compatibility with System V Release 3.1, a semicolon (;) may be used to separate the rule from the rest of the specification.
If the
TZ
environment variable does not specify a
tzfile(5)
format file and cannot be interpreted as a direct specification, UTC
is used.
/etc/localtime
/usr/share/zoneinfo
/usr/share/zoneinfo/posixrules
/usr/share/zoneinfo/GMT
If
/usr/share/zoneinfo/GMT
is absent, UTC leap seconds are loaded from
/usr/share/zoneinfo/posixrules
.