CRON(8) System Manager's Manual CRON(8)
cron - clock daemon
Cron executes commands at specified dates and times according to the
instructions in the file /usr/lib/crontab. Since cron never exits, it
should only be executed once. This is best done by running cron from
the initialization process through the file /etc/rc; see init(8).
Crontab consists of lines of six fields each. The fields are separated
by spaces or tabs. The first five are integer patterns to specify the
minute (0-59), hour (0-23), day of the month (1-31), month of the year
(1-12), and day of the week (1-7 with 1=Monday). Each of these pat-
terns may contain a number in the range above; two numbers separated by
a minus meaning a range inclusive; a list of numbers separated by com-
mas meaning any of the numbers; or an asterisk meaning all legal val-
ues. The sixth field is a string that is executed by the Shell at the
specified times. A percent character in this field is translated to a
new-line character. Only the first line (up to a % or end of line) of
the command field is executed by the Shell. The other lines are made
available to the command as standard input.
Crontab is examined by cron every minute.
4 February 1983 CRON(8)