NAME
cron - clock daemon

SYNOPSIS
/etc/cron

DESCRIPTION
Cron executes commands at specified dates and times according to
the instructions in the files /usr/lib/crontab and
/usr/lib/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:

minute (0-59)
hour (0-23)
day of the month (1-31)
month of the year (1-12)
day of the week (1-7 with 1 = Monday)

Each of these patterns may contain:

a number in the range above
two numbers separated by a minus meaning a range inclusive
a list of numbers separated by commas meaning any of the numbers
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
/usr/lib/crontab
/usr/lib/crontab.local