Merging upstream version 6.8.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 244 insertions, 0 deletions

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+'\" t
+.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
+.\"
+.\" SPDX-License-Identifier: Linux-man-pages-copyleft
+.\"
+.\" References consulted:
+.\"     Linux libc source code
+.\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
+.\"     386BSD man pages
+.\" Modified Sun Jul 25 11:01:58 1993 by Rik Faith (faith@cs.unc.edu)
+.\" Modified 2001-11-13, aeb
+.\" Modified 2004-12-01 mtk and Martin Schulze <joey@infodrom.org>
+.\"
+.TH tzset 3 2024-05-02 "Linux man-pages (unreleased)"
+.SH NAME
+tzset, tzname, timezone, daylight \- initialize time conversion information
+.SH LIBRARY
+Standard C library
+.RI ( libc ", " \-lc )
+.SH SYNOPSIS
+.nf
+.B #include <time.h>
+.P
+.B void tzset(void);
+.P
+.BI "extern char *" tzname [2];
+.BI "extern long " timezone ;
+.BI "extern int " daylight ;
+.fi
+.P
+.RS -4
+Feature Test Macro Requirements for glibc (see
+.BR feature_test_macros (7)):
+.RE
+.P
+.BR tzset ():
+.nf
+    _POSIX_C_SOURCE
+.fi
+.P
+.IR tzname :
+.nf
+    _POSIX_C_SOURCE
+.fi
+.P
+.IR timezone ,
+.IR daylight :
+.nf
+    _XOPEN_SOURCE
+        || /* glibc >= 2.19: */ _DEFAULT_SOURCE
+        || /* glibc <= 2.19: */ _SVID_SOURCE
+.fi
+.SH DESCRIPTION
+The
+.BR tzset ()
+function initializes the \fItzname\fP variable from the
+.B TZ
+environment variable.
+This function is automatically called by the
+other time conversion functions that depend on the timezone.
+In a System-V-like environment, it will also set the variables \fItimezone\fP
+(seconds West of UTC) and \fIdaylight\fP (to 0 if this timezone does not
+have any daylight saving time rules, or to nonzero if there is a time,
+past, present, or future when daylight saving time applies).
+.P
+If the
+.B TZ
+variable does not appear in the environment, the system timezone is used.
+The system timezone is configured by copying, or linking, a file in the
+.BR tzfile (5)
+format to
+.IR /etc/localtime .
+A timezone database of these files may be located in the system
+timezone directory (see the \fBFILES\fP section below).
+.P
+If the
+.B TZ
+variable does appear in the environment, but its value is empty,
+or its value cannot be interpreted using any of the formats specified
+below, then Coordinated Universal Time (UTC) is used.
+.P
+The value of
+.B TZ
+can be one of two formats.
+The first format is a string of characters that directly represent the
+timezone to be used:
+.P
+.in +4n
+.EX
+.IR "std offset" [ dst [ offset ][, start [ /time ], end [ /time ]]]
+.EE
+.in
+.P
+There are no spaces in the specification.
+The \fIstd\fP string specifies an abbreviation for the timezone and must be
+three or more alphabetic characters.
+When enclosed between the less-than (<) and greater-than (>) signs, the
+character set is expanded to include the plus (+) sign, the minus (\-)
+sign, and digits.
+The \fIoffset\fP string immediately
+follows \fIstd\fP and specifies the time value to be added to the local
+time to get Coordinated Universal Time (UTC).
+The \fIoffset\fP is positive
+if the local timezone is west of the Prime Meridian and negative if it is
+east.
+The hour must be between 0 and 24, and the minutes and seconds 00 and 59:
+.P
+.in +4n
+.EX
+.RI [ + | \- ] hh [ :mm [ :ss ]]
+.EE
+.in
+.P
+The \fIdst\fP string and \fIoffset\fP specify the name and offset for the
+corresponding daylight saving timezone.
+If the offset is omitted,
+it defaults to one hour ahead of standard time.
+.P
+The \fIstart\fP field specifies when daylight saving time goes into
+effect and the \fIend\fP field specifies when the change is made back to
+standard time.
+These fields may have the following formats:
+.TP
+J\fIn\fP
+This specifies the Julian day with \fIn\fP between 1 and 365.
+Leap days are not counted.
+In this format, February 29 can't be represented;
+February 28 is day 59, and March 1 is always day 60.
+.TP
+.I n
+This specifies the zero-based Julian day with \fIn\fP between 0 and 365.
+February 29 is counted in leap years.
+.TP
+M\fIm\fP.\fIw\fP.\fId\fP
+This specifies day \fId\fP (0 <= \fId\fP <= 6) of week \fIw\fP
+(1 <= \fIw\fP <= 5) of month \fIm\fP (1 <= \fIm\fP <= 12).
+Week 1 is
+the first week in which day \fId\fP occurs and week 5 is the last week
+in which day \fId\fP occurs.
+Day 0 is a Sunday.
+.P
+The \fItime\fP fields specify when, in the local time currently in effect,
+the change to the other time occurs.
+If omitted, the default is 02:00:00.
+.P
+Here is an example for New Zealand,
+where the standard time (NZST) is 12 hours ahead of UTC,
+and daylight saving time (NZDT), 13 hours ahead of UTC,
+runs from the first Sunday in October to the third Sunday in March,
+and the changeovers happen at the default time of 02:00:00:
+.P
+.in +4n
+.EX
+TZ="NZST\-12:00:00NZDT\-13:00:00,M10.1.0,M3.3.0"
+.EE
+.in
+.P
+The second format specifies that the timezone information should be read
+from a file:
+.P
+.in +4n
+.EX
+:[filespec]
+.EE
+.in
+.P
+If the file specification \fIfilespec\fP is omitted, or its value cannot
+be interpreted, then Coordinated Universal Time (UTC) is used.
+If \fIfilespec\fP is given, it specifies another
+.BR tzfile (5)-format
+file to read the timezone information from.
+If \fIfilespec\fP does not begin with a \[aq]/\[aq], the file specification is
+relative to the system timezone directory.
+If the colon is omitted each
+of the above \fBTZ\fP formats will be tried.
+.P
+Here's an example, once more for New Zealand:
+.P
+.in +4n
+.EX
+TZ=":Pacific/Auckland"
+.EE
+.in
+.SH ENVIRONMENT
+.TP
+.B TZ
+If this variable is set its value takes precedence over the system
+configured timezone.
+.TP
+.B TZDIR
+If this variable is set its value takes precedence over the system
+configured timezone database directory path.
+.SH FILES
+.TP
+.I /etc/localtime
+The system timezone file.
+.TP
+.I /usr/share/zoneinfo/
+The system timezone database directory.
+.TP
+.I /usr/share/zoneinfo/posixrules
+When a TZ string includes a dst timezone without anything following it,
+then this file is used for the start/end rules.
+It is in the
+.BR tzfile (5)
+format.
+By default, the zoneinfo Makefile hard links it to the
+.IR America/New_York " tzfile."
+.P
+Above are the current standard file locations, but they are
+configurable when glibc is compiled.
+.SH ATTRIBUTES
+For an explanation of the terms used in this section, see
+.BR attributes (7).
+.TS
+allbox;
+lbx lb lb
+l l l.
+Interface	Attribute	Value
+T{
+.na
+.nh
+.BR tzset ()
+T}	Thread safety	MT-Safe env locale
+.TE
+.SH STANDARDS
+POSIX.1-2008.
+.SH HISTORY
+POSIX.1-2001, SVr4, 4.3BSD.
+.P
+4.3BSD had a function
+.BI "char *timezone(" zone ", " dst )
+that returned the
+name of the timezone corresponding to its first argument (minutes
+West of UTC).
+If the second argument was 0, the standard name was used,
+otherwise the daylight saving time version.
+.SH SEE ALSO
+.BR date (1),
+.BR gettimeofday (2),
+.BR time (2),
+.BR ctime (3),
+.BR getenv (3),
+.BR tzfile (5)