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tz(5) [minix man page]

TZ(5)								File Formats Manual							     TZ(5)

TZ - Time zone environment variable SYNOPSIS
TZ=zone[-]offset[dst[offset][,start[/time],end[/time]]] DESCRIPTION
The TZ environment variable tells functions such as the ctime(3) family and programs like date what the time zone and daylight saving rule is. The value of TZ has the POSIX standardized form shown in the synopsis. This form specifies the zone names, offsets from GMT, and day- light savings changeover times for at least the current year. zone A three or more letter name for the time zone in normal (winter) time. [-]offset A signed time telling the offset of the time zone westwards from Greenwich. The time has the form hh[:mm[:ss]] with a one of two digit hour, and optional two digit minutes and seconds. dst The name of the time zone when daylight savings is in effect. It may be followed by an offset telling how big the clock correction is other than the default of 1 hour. start/time,end/time Specifies the start and end of the daylight savings period. The start and end fields indicate on what day the changeover occurs. They must be in one of the following formats: Jn The Julian day n (1 <= n <= 365) ignoring leap days, i.e. there is no February 29. n The zero-based Julian day (0 <= n <= 365). Leap days are not ignored. Mm.n.d This indicates month m, the n-th occurrence of day d (1 <= m <= 12, 1 <= n <= 5, 0 <= d <= 6, 0=Sunday). The 5-th occurrence means the last occurrence of that day in a month. So M4.1.0 is the first Sunday in April, M9.5.0 is the last Sunday in Septem- ber. The time field indicates the time the changeover occurs on the given day. EXAMPLES
Greenwich Mean Time: TZ=GMT0 Middle European Time, 1 hour east from Greenwich, daylight savings starts on the last Sunday in March at 2 AM and ends on the last Sunday in October at 3 AM: TZ='MET-1MET DST,M3.5.0/2,M10.5.0/3' British time, daylight savings starts and ends at the same moment as MET, but in an earlier time zone: TZ=GMT0BST,M3.5.0/1,M10.5.0/2 The eastern european time zones also have the changeovers at the same absolute time as British time and MET. U.S. Eastern Standard Time, 5 hours west from Greenwich, daylight savings starts on the first Sunday in April at 2 AM and ends on the last Sunday in October at 2 AM: TZ=EST5EDT,M4.1.0/2,M10.5.0/2 It shouldn't surprise you that daylight savings in New Zealand is observed in the months opposite from the previous examples. It starts on the first Sunday in October at 2 AM and ends on the third Sunday in March at 3 AM: TZ=NZST-12NZDT,M10.1.0/2,M3.3.0/3 SEE ALSO
readclock(8), date(1). BUGS
You may have noticed that many fields are optional. Do no omit them, because the defaults are bogus. If you need daylight savings then fully specify the changeovers. West is negative, east is positive, ask any sailor. AUTHOR
Kees J. Bot ( TZ(5)

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TZSET(3)						     Linux Programmer's Manual							  TZSET(3)

tzset, tzname, timezone, daylight - initialize time conversion information SYNOPSIS
#include <time.h> void tzset (void); extern char *tzname[2]; extern long timezone; extern int daylight; Feature Test Macro Requirements for glibc (see feature_test_macros(7)): tzset(): _POSIX_C_SOURCE >= 1 || _XOPEN_SOURCE || _POSIX_SOURCE tzname: _POSIX_C_SOURCE >= 1 || _XOPEN_SOURCE || _POSIX_SOURCE timezone: _SVID_SOURCE || _XOPEN_SOURCE daylight: _SVID_SOURCE || _XOPEN_SOURCE DESCRIPTION
The tzset() function initializes the tzname variable from the 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 timezone (seconds West of UTC) and daylight (to 0 if this timezone does not have any daylight saving time rules, or to nonzero if there is a time during the year when daylight saving time applies). If the TZ variable does not appear in the environment, the tzname variable is initialized with the best approximation of local wall clock time, as specified by the tzfile(5)-format file localtime found in the system timezone directory (see below). (One also often sees /etc/localtime used here, a symlink to the right file in the system timezone directory.) If the TZ variable does appear in the environment but its value is empty or its value cannot be interpreted using any of the formats speci- fied below, Coordinated Universal Time (UTC) is used. 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 timezone: std offset The std string specifies the name of the timezone and must be three or more alphabetic characters. The offset string immediately follows std and specifies the time value to be added to the local time to get Coordinated Universal Time (UTC). The offset 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 0 and 59. The second format is used when there is daylight saving time: std offset dst [offset],start[/time],end[/time] There are no spaces in the specification. The initial std and offset specify the standard timezone, as described above. The dst string and offset specify the name and offset for the corresponding daylight saving timezone. If the offset is omitted, it default to one hour ahead of standard time. The start field specifies when daylight saving time goes into effect and the end field specifies when the change is made back to standard time. These fields may have the following formats: Jn This specifies the Julian day with n between 1 and 365. Leap days are not counted. In this format, February 29 can't be repre- sented; February 28 is day 59, and March 1 is always day 60. n This specifies the zero-based Julian day with n between 0 and 365. February 29 is counted in leap years. Mm.w.d This specifies day d (0 <= d <= 6) of week w (1 <= w <= 5) of month m (1 <= m <= 12). Week 1 is the first week in which day d occurs and week 5 is the last week in which day d occurs. Day 0 is a Sunday. The time 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. 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: TZ="NZST-12:00:00NZDT-13:00:00,M10.1.0,M3.3.0" The third format specifies that the timezone information should be read from a file: :[filespec] If the file specification filespec is omitted, the timezone information is read from the file localtime in the system timezone directory, which nowadays usually is /usr/share/zoneinfo. This file is in tzfile(5) format. If filespec is given, it specifies another tzfile(5)-format file to read the timezone information from. If filespec does not begin with a '/', the file specification is relative to the system timezone directory. Here's an example, once more for New Zealand: TZ=":Pacific/Auckland" FILES
The system timezone directory used depends on the (g)libc version. Libc4 and libc5 use /usr/lib/zoneinfo, and, since libc-5.4.6, when this doesn't work, will try /usr/share/zoneinfo. Glibc2 will use the environment variable TZDIR, when that exists. Its default depends on how it was installed, but normally is /usr/share/zoneinfo. This timezone directory contains the files localtime local timezone file posixrules rules for POSIX-style TZ's Often /etc/localtime is a symlink to the file localtime or to the correct timezone file in the system timezone directory. CONFORMING TO
SVr4, POSIX.1-2001, 4.3BSD. NOTES
Note that the variable daylight does not indicate that daylight saving time applies right now. It used to give the number of some algo- rithm (see the variable tz_dsttime in gettimeofday(2)). It has been obsolete for many years but is required by SUSv2. 4.3BSD had a function 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. SEE ALSO
date(1), gettimeofday(2), time(2), ctime(3), getenv(3), tzfile(5) COLOPHON
This page is part of release 3.44 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at 2012-03-25 TZSET(3)
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