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[unix-history] / usr / src / usr.sbin / cron / cron.8

.\"	@(#)cron.8	6.4 (Berkeley) %G%
.\"
.TH CRON 8 ""
.AT 3
.SH NAME
cron \- clock daemon
.SH SYNOPSIS
.B /etc/cron
.SH DESCRIPTION
.I 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
.I cron
never exits,
it should only be executed once.
This is best done by running
.I cron
from the initialization
process through the file
/etc/rc;
see
.IR init (8).
.PP
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:
.in +2m
.TP 2m
\(bu
minute (0-59)
.nr .0 \n()Pu
.nr )P 0
.TP 2m
\(bu
hour (0-23)
.TP 2m
\(bu
day of the month (1-31)
.TP 2m
\(bu
month of the year (1-12)
.TP 2m
\(bu
day of the week (1-7 with 1 = Monday)
.nr )P \n(.0u
.in -2m
.LP
Each of these patterns may contain:
.in +2m
.TP 2m
\(bu
a number in the range above
.nr .0 \n()Pu
.nr )P 0
.TP 2m
\(bu
two numbers separated by a minus
meaning a range inclusive
.TP 2m
\(bu
a list of numbers separated by
commas meaning any of the numbers
.TP 2m
\(bu
an asterisk meaning all legal values
.nr )P \n(.0u
.in -2m
.LP
The sixth field is a user name: the
command will be run ``as'' that 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
which is executed by the Shell at the
specified times.
A percent character (``%'')
in this field is translated to a new-line
character.
.PP
Both
crontab files are checked by
.I cron
every minute, on the minute.
.SH FILES
/usr/lib/crontab
.br
/usr/lib/crontab.local