bsd man page for cron

CRON(8) 						      System Manager's Manual							   CRON(8)

NAME
       cron - clock daemon

SYNOPSIS
       /usr/sbin/cron

DESCRIPTION
       Cron  executes commands at specified dates and times according to the instructions in the files /etc/crontab and /etc/crontab.local.  None,
       either one, or both of these files may be present.  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).

       The  crontab files consist of lines of seven fields each.  The fields are separated by spaces or tabs.  The first five are integer patterns
       to specify:

       o minute (0-59)

       o hour (0-23)

       o day of the month (1-31)

       o month of the year (1-12)

       o day of the week (1-7 with 1 = Monday)

       Each of these patterns may contain:

       o a number in the range above

       o two numbers separated by a minus meaning a range inclusive

       o a list of numbers separated by commas meaning any of the numbers

       o an asterisk meaning all legal values

       The sixth field is a user name: the command will be run with that user's uid and permissions.  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 which is executed by the Shell at the
       specified times.  A percent character (``%'') in this field is translated to a new-line character.

       Both crontab files are checked by cron every minute, on the minute.

FILES
       /etc/crontab
       /etc/crontab.local

7th Edition							 October 23, 1996							   CRON(8)