CRON(8) BSD CRON(8)
NAME
cron - clock daemon
SYNOPSIS
/etc/cron
DESCRIPTION
The cron command executes commands at the dates and times specified in
the files /usr/lib/crontab, and /usr/lib/crontab.local. None, either
one, or both of these files may be present. Since cron doesn't exit, it
should be executed only once. This is best done by running cron from the
initialization process, using an entry in the /etc/rc file.
The crontab files consist of lines with seven fields each; the fields are
separated by spaces or tabs. The first five fields contain integer
patterns that specify the time and date in the following format:
Minute (0-59)
Hour (0-23)
Day of the month (1-31)
Month of the year (1-12)
Day of the week (1-7, 1 is Monday)
Each of these patterns may contain
⊕ A number in the range above
⊕ Two numbers separated by a minus sign, indicating an inclusive range
⊕ A list of numbers separated by commas, meaning any of the numbers
⊕ An asterisk, meaning all legal values for that field.
For example, if the month field contains:
1,3,5
cron will execute at all times in January, March, and May when the other
fields' values are true.
The sixth field is a username; cron will execute the command with the
permissions and uid of the specified user.
The seventh field consists of all the text on a line following the sixth
field, including spaces and tabs. This text is treated as a command that
is executed by the Shell at the time(s) and date(s) specified. A percent
character (%) in this field is translated to a new-line character.
cron checks the files /usr/lib/crontab and /usr/lib/crontab.local every
minute, on the minute.
EXAMPLE
A line of the form
0,15,30,45 * * * * root /usr/lib/atrun
in the /usr/lib/crontab file will run the atrun program every 15 minutes.
FILES
/usr/lib/crontab
/usr/lib/crontab.local files of times, dates, and commands to be run