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.\" @(#)tzset.3 5.3 (Berkeley) 7/23/91
.Nd initialize time conversion information
initializes time conversion information used by the library routine
specifies how this is done.
does not appear in the environment, the best available approximation to
local wall clock time, as specified by the
appears in the environment but its value is a null string, Coordinated
is used (without leap second correction).
appears in the environment and its value begins with a colon
the rest of its value is used as a pathname of a
file from which to read the time conversion information.
If the first character of the pathname is a slash
an absolute pathname; otherwise, it is used as a pathname relative to
the system time conversion information directory.
If its value does not begin with a colon, it is first used as the pathname
of a file (as described above) from which to read the time conversion
If that file cannot be read, the value is then interpreted as a direct
specification (the format is described below) of the time conversion
environment variable does not specify a
file and cannot be interpreted as a direct specification,
returns the best available approximation of local wall clock time.
is used directly as a specification of the time conversion information,
it must have the following syntax (spaces inserted for clarity):
.Bd -filled -offset indent
.Bl -tag -width std_and_dst -offset indent
Three or more bytes that are the designation for the standard
is missing, then summer time does not apply in this locale.
Upper and lowercase letters are explicitly allowed. Any characters
Indicates the value one must add to the local time to arrive at
Coordinated Universal Time. The
.Bd -unfilled -offset indent
is required and may be a single digit. The
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) \(em if present \(em 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
Indicates when to change to and back from summer time. The
.Bd -filled -offset indent
describes when the change from standard to summer time occurs and the
describes when the change back happens. Each
field describes when, in current local time, the change to the other
.Bl -tag -width "M.m.n.d"
Leap days are not counted; that is, in all years \(em including leap
years \(em February 28 is day 59 and March 1 is day 60. It is
impossible to explicitly refer to the occasional February 29.
The zero-based Julian day
Leap days are counted, and it is possible to refer to February 29.
which may occur in either the fourth or the fifth week). Week 1 is the
day occurs. Day zero is Sunday.
except that no leading sign
is allowed. The default, if
specification, the rules specified
in the system time conversion information directory are used, with the
standard and summer time offsets from
replaced by those specified by
For compatibility with System V Release 3.1, a semicolon
may be used to separate the
from the rest of the specification.
.Bl -tag -width /usr/share/zoneinfo/posixrules -compact
.It Pa /usr/share/zoneinfo
.It Pa /usr/share/zoneinfo/posixrules
.It Pa /usr/share/zoneinfo/GMT for
.Pa /usr/share/zoneinfo/GMT
leap seconds are loaded from
.Pa /usr/share/zoneinfo/posixrules .