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Daylight savings time
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tztab(4) Kernel Interfaces Manual tztab(4) NAME
tztab - 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 simul- taneously 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 number 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. EXTERNAL INFLUENCES
International Code Set Support Single-byte character code sets are supported. EXAMPLES
The time zone adjustment table for the Eastern Time Zone in the United States is: 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). AUTHOR
was developed by HP. FILES
SEE ALSO
date(1), ctime(3C), environ(5). tztab(4)
