cron(1M) Maintenance Commands cron(1M)
NAME
cron - clock daemon
SYNOPSIS
/usr/sbin/cron
AVAILABILITY
SUNWcsr
DESCRIPTION
The cron command starts a process that executes commands at
specified dates and times. Regularly scheduled commands can
be specified according to instructions found in crontab
files in the directory /var/spool/cron/crontabs. Users can
submit their own crontab file using the crontab(1) command.
Commands which are to be executed only once may be submitted
using the at(1) command.
cron only examines crontab or at command files during its
own process initialization phase and when the crontab or at
command is run. This reduces the overhead of checking for
new or changed files at regularly scheduled intervals.
Since cron never exits, it should be executed only once.
This is done routinely through /etc/rc2.d/S75cron at system
boot time. The file /etc/cron.d/FIFO is used (among other
things) as a lock file to prevent the execution of more than
one instance of cron.
cron captures the output of the job's stdout and stderr
streams, and, if it is non-empty, mails the output to the
user. If the job does not produce output, no mail is sent
to the user (unless the job is an at(1) job and the -m
option was specified when the job was submitted).
Setting cron Defaults
To keep a log of all actions taken by cron, CRONLOG=YES (by
default) must be specified in the /etc/default/cron file.
If CRONLOG=NO is specified, no logging is done. Keeping the
log is a user configurable option since cron usually creates
huge log files.
The PATH for user cron jobs can be set using PATH= in
/etc/default/cron. The PATH for root cron jobs can be set
using SUPATH= in /etc/default/cron. The security implica-
tions of setting PATH and SUPATH should be carefully con-
sidered.
Example /etc/default/cron file:
CRONLOG=YES
PATH=/usr/bin:/usr/ucb:
This example enables logging and sets the default PATH used
by non-root jobs to /usr/bin:/usr/ucb:. Root jobs will con-
tinue to use /usr/sbin:/usr/bin.
/etc/cron.d/logchecker is a script that checks to see if the
log file has exceeded the system ulimit. If so, the log
file is moved to /var/cron/olog.
FILES
/etc/cron.d main cron directory
/etc/cron.d/FIFO used as a lock file
/etc/default/cron contains cron default settings
/var/cron/log cron history information
/var/spool/cron spool area
/etc/cron.d/logchecker moves log file to /var/cron/olog if
log file exceeds system ulimit.
/etc/cron.d/queuedefs queue description file for at,
batch, and cron.
SEE ALSO
at(1), crontab(1), sh(1), queuedefs(4)
DIAGNOSTICS
A history of all actions taken by cron is stored in
/var/cron/log and (possibly) /var/cron/olog.
SunOS 5.4 Last change: 1 Mar 1994