TZ(M) XENIX System V TZ(M)
Name
TZ - Time zone environment variable.
Syntax
TZ=sssn[ddd[m][;start[/time],end[/time]]] ; export TZ
setenv TZ sssn[ddd[m][;start[/time],end[/time]]]
/etc/tz
Description
TZ is the shell environment variable for the time zone of
the system and is set in the files /etc/rc, /.profile, and
/etc/default/login.
The shell script /etc/tz, generally run during installation,
prompts for the correct time zone and makes the changes in
the appropriate files.
/etc/tz also prompts for the dates when time is shifted from
standard to daylight time and back, and for the number of
hours to shift (partial hours in the form of hh:mm:ss are
acceptable).
Users living in a time zone different than that of the host
machine may change TZ in their $HOME/.profile or
$HOME/.login files.
TZ contains the following information:
(sss) One to nine letters designating the standard
time zone.
(n) Number of hours past Greenwich mean time for the
standard time (partial hours are valid e.g.
12:30:01). Positive hours are west of Greenwich,
negative numbers are east of Greeenwich.
(ddd) One to nine letters designating the local
daylight savings time (summer time) zone. If not
present, summer time is assumed not to apply.
(m) Number of hours past Greenwich mean time for the
summer time (partial hours are valid e.g.
11:30:01). Positive hours are west of
Greenwich, negative numbers are east of
Greeenwich. If m is not given, the distance to
GMT during summer time is assumed to be one hour
less than during standard time.
(start) The rule defining the day summer time begins.
In the southern hemisphere, the ending day will
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be earlier in the year than the starting day.
(end) The rule defining the day summer time ends.
(time) The time of day the change to and from summer
time occurs. The default is 02:00:00 local time.
The rules for defining the start and end of summer time are
as follows:
Jn 1 based Julian day n (1 _ n _ 365)*
n 0 based Julian day n (0 _ n _ 364)*
Wn.d nth (1 _ n _ 53)- day of week d (0 _ d _ 6)**
Mm.n.d nth (1 _ n _ 5)= day of week d in month m (1 _ m _ 12)**
* Leap days (February 29) are never counted; that is,
February 28 (J59) is immediately followed by March 1
(J60) even in leap years.
** Sunday is the first day of the week (0). If d is omitted,
Sunday is assumed.
- The 5th week of the month is always the last week
containing day d, whether there are actually 4 or 5 weeks
containing day d.
= The 53rd week of the year is always the last week
containing day d, whether there are actually 52 or 53
weeks containing day d.
If start and end are omitted, current U.S. law is assumed.
For the simple expression of Eastern Standard/Daylight Time
TZ is set as follows:
TZ=EST5EDT ; export TZ
(for sh(C) and vsh(C))
setenv TZ EST5EDT
(for csh(C))
The fully expressed TZ string for Eastern Standard/Daylight
Time using the current U.S. law of changing to daylight
saving time on the first Sunday in April, and back to
standard time on the Sunday week in October at 2:00 a.m.
local time would be:
TZ=EST05:00:00EDT04:00:00;M4.1.0/02:00:00,M10.5.0/02:00:00
To change the time zone for the entire system, run the shell
script /etc/tz (as root) or use an editor to change the
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variable TZ in the files /etc/rc, /.profile and
/etc/default/login. In /etc/rc the line changing the time
zone (see the sh example above) must occur before the
/etc/asktime command. The TZ variable in /etc/default/login
causes the time zone to be set correctly on logging in and
for programs such as uucico.
Files
/etc/rc
/etc/default/login
/etc/tz
$HOME/.profile
$HOME/.login
See Also
environ(M), date(C), ctime(S)
Notes
The date(C) automatically switches from Standard Time to
Summer Time (Daylight Saving Time). Leap days are properly
accounted for.
Changes to TZ are immediately effective, (i.e. if a process
changes the TZ variable, the next call to a ctime(S) routine
returns a value based on the new value of the variable).
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