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diff --git a/man3/tzset.3 b/man3/tzset.3 new file mode 100644 index 000000000..171b98abf --- /dev/null +++ b/man3/tzset.3 @@ -0,0 +1,173 @@ +.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk) +.\" +.\" Permission is granted to make and distribute verbatim copies of this +.\" manual provided the copyright notice and this permission notice are +.\" preserved on all copies. +.\" +.\" Permission is granted to copy and distribute modified versions of this +.\" manual under the conditions for verbatim copying, provided that the +.\" entire resulting derived work is distributed under the terms of a +.\" permission notice identical to this one. +.\" +.\" Since the Linux kernel and libraries are constantly changing, this +.\" manual page may be incorrect or out-of-date. The author(s) assume no +.\" responsibility for errors or omissions, or for damages resulting from +.\" the use of the information contained herein. The author(s) may not +.\" have taken the same level of care in the production of this manual, +.\" which is licensed free of charge, as they might when working +.\" professionally. +.\" +.\" Formatted or processed versions of this manual, if unaccompanied by +.\" the source, must acknowledge the copyright and authors of this work. +.\" +.\" 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 +.TH TZSET 3 2001-11-13 "" "Linux Programmer's Manual" +.SH NAME +tzset, tzname, timezone, daylight \- initialize time conversion information +.SH SYNOPSIS +.nf +.B #include <time.h> +.sp +.B void tzset (void); +.sp +.BI "extern char *" tzname [2]; +.BI "extern long " timezone ; +.BI "extern int " daylight ; +.fi +.SH DESCRIPTION +The \fBtzset()\fP function initializes the \fItzname\fP variable from the +TZ environment variable. This function is automatically called by the +other time conversion functions that depend on the time zone. +In a SysV-like environment it will also set the variables \fItimezone\fP +(seconds West of GMT) and \fIdaylight\fP (0 if this time zone does not +have any daylight savings time rules, nonzero if there is a time during +the year when daylight savings time applies). +.PP +If the TZ variable does not appear in the environment, the \fItzname\fP +variable is initialized with the best approximation of local wall clock +time, as specified by the +.BR tzfile (5)-format +file \fIlocaltime\fP +found in the system timezone directory (see below). +(One also often sees +.I /etc/localtime +used here, a symlink to the right file in the system timezone directory.) +.PP +If the TZ variable does appear in the environment but its value is NULL +or its value cannot be interpreted using any of the formats specified +below, Coordinated Universal Time (UTC) is used. +.PP +The value of TZ can be one of three formats. The first format is used +when there is no daylight saving time in the local time zone: +.sp +.RS +.I std offset +.RE +.sp +The \fIstd\fP string specifies the name of the time zone and must be +three or more alphabetic characters. 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 time zone 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 +0 and 59. +.PP +The second format is used when there is daylight saving time: +.sp +.RS +.I std offset dst [offset],start[/time],end[/time] +.RE +.sp +There are no spaces in the specification. The initial \fIstd\fP and +\fIoffset\fP specify the standard time zone, as described above. The +\fIdst\fP string and \fIoffset\fP specify the name and offset for the +corresponding daylight savings time zone. If the offset is omitted, +it defaults to one hour ahead of standard time. +.PP +The \fIstart\fP field specifies when daylight savings 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. February +29 is never counted even in leap years. +.TP +.I n +This specifies the Julian day with \fIn\fP between 1 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. +.PP +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. +.PP +The third format specifies that the time zone information should be read +from a file: +.sp +.RS +:[filespec] +.RE +.sp +If the file specification \fIfilespec\fP is omitted, the time zone +information is read from the file +.I localtime +in the system timezone directory, which nowadays usually is +.IR /usr/share/zoneinfo . +This file is in +.BR tzfile (5) +format. If \fIfilespec\fP is given, it specifies another +.BR tzfile (5)-format +file to read the time zone information from. If +\fIfilespec\fP does not begin with a `/', the file specification is +relative to the system timezone directory. +.SH FILES +The system time zone directory used depends on the (g)libc version. +Libc4 and libc5 use +.IR /usr/lib/zoneinfo , +and, since libc-5.4.6, +when this doesn't work, will try +.IR /usr/share/zoneinfo . +Glibc2 will use the environment variable TZDIR, when that exists. +Its default depends on how it was installed, but normally is +.IR /usr/share/zoneinfo . +.LP +This timezone directory contains the files +.nf +localtime local time zone file +posixrules rules for POSIX-style TZ's +.fi +.LP +Often +.I /etc/localtime +is a symlink to the file +.I localtime +or to the correct time zone file in the system time zone directory. +.SH "CONFORMING TO" +SVID 3, POSIX, BSD 4.3 +.SH NOTES +Note that the variable \fIdaylight\fP does not indicate that daylight +savings time applies right now. It used to give the number of some +algorithm (see the variable \fItz_dsttime\fP in +.BR gettimeofday (2)). +It has been obsolete for many years but is required by SUSv2. +.LP +BSD4.3 had a routine \fIchar *timezone(zone,dst)\fP that returned the +name of the time zone corresponding to its first argument (minutes +West of GMT). If the second argument was 0, the standard name was used, +otherwise the daylight savings time version. +.SH "SEE ALSO" +.BR date (1), +.BR gettimeofday (2), +.BR time (2), +.BR ctime (3), +.BR getenv (3), +.BR tzfile (5) |