tztab(4)tztab(4)NAMEtztab - time zone adjustment table for date and ctime()DESCRIPTION
The file describes the differences between Coordinated Universal Time
(UTC) and local time. Several local areas can be represented simulta‐
neously with historical detail.
The file consists of one or more time zone adjustment entries. The
first line of the entry contains a unique string that may match the
value of the string in the user's environment. The format is where is
the time zone name or abbreviation, diff is the difference in hours
from UTC, and is the name or abbreviation of the "Daylight Savings"
time zone. Fractional values of diff are expressed in minutes preceded
by a colon. Each such string will start with an alphabetic character.
The second and subsequent lines of each entry details the time zone
adjustments for that time zone. The lines contain seven fields each.
The first six fields specify the first minute in which the time zone
adjustment, specified in the seventh field, applies. The fields are
separated by spaces or tabs. The first six are integer patterns that
specify the minute (0-59), hour (0-23), day of the month (1-31), month
of the year (1-12), year (1970-2038), and day of the week (0-6, with
0=Sunday). The minute, hour, and month of the year must contain a num‐
ber in the (respective) range indicated above. The day of the month,
year, and day of the week can contain a number as above or two numbers
separated by a minus (indicating an inclusive range). Either the day
of the month or the day of the week field must be a range, the other
must be simple number.
The seventh field is a string that describes the time zone adjustment
in its simplest form: where is an alphabetic string giving the time
zone name or abbreviation, and diff is the difference in hours from
UTC. must match either the field or the field in the first line of the
time zone adjustment entry. Any fractional diff is shown in minutes.
Comments begin with a in the first column, and include all characters
up to a newline. Comments are ignored.
International Code Set Support
Single-byte character code sets are supported.
The time zone adjustment table for the Eastern Time Zone in the United
Normally (as indicated in the first line) Eastern Standard Time is five
hours earlier than UTC. During Daylight Savings time, it changes to a
4 hour difference. The first time Daylight Savings Time took effect
(second line) was on January 6, 1974 at 3:00 a.m., EDT. Note that the
minute before was 1:59 a.m., EST. The change back to standard time
took effect (sixth line) on the last Sunday in November of the same
year. At that point, the time went from 1:59 a.m., EDT to 1:00 a.m.,
EST. The transition to Daylight Savings Time since then has gone from
the last Sunday in February (third line) to the last Sunday in April
(fourth line) to the first Sunday in April (fifth line). The return to
standard time for the same period has remained at the last Sunday in
October (seventh line).
was developed by HP.
FILESSEE ALSOdate(1), ctime(3C), environ(5).