cron - clock daemon
cron starts a process that executes commands at specified
dates and times.
You can specify regularly scheduled commands to cron accord-
ing 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 can 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.
As cron never exits, it should be executed only once. This
is done routinely by way of the /etc/rc2.d/S75cron file at
system boot time. The file /etc/cron.d/FIFO file is used 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 not empty, mails the output to the
user. If the job does not produce output, no mail is sent to
the user. An exception is if the job is an at(1) job and the
-m option was specified when the job was submitted.
cron and at jobs are not executed if your account is locked.
Jobs and processses execute. The shadow(4) file defines
which accounts are not locked and will have their jobs and
Setting cron Jobs Across Timezones
The timezone of the cron daemon sets the system-wide
timezone for cron entries. This, in turn, is by set by
default system-wide using /etc/default/init.
If some form of daylight savings or summer/winter time is in
effect, then jobs scheduled during the switchover period
could be executed once, twice, or not at all.
Setting cron Defaults
To keep a log of all actions taken by cron, you must specify
CRONLOG=YES in the /etc/default/cron file. If you specify
CRONLOG=NO, no logging is done. Keeping the log is a user
configurable option since cron usually creates huge log
You can specify the PATH for user cron jobs by using PATH=
in /etc/default/cron. You can set the PATH for root cron
jobs using SUPATH= in /etc/default/cron. Carefully consider
the security implications of setting PATH and SUPATH.
Example /etc/default/cron file:
This example enables logging and sets the default PATH used
by non-root jobs to /usr/bin:/usr/ucb:. Root jobs continue
to use /usr/sbin:/usr/bin.
The cron log file is periodically rotated by logadm(1M).
Main cron directory
cron default settings file
cron history information
Queue description file for at, batch, and cron
Configuration file for logadm
See attributes(5) for descriptions of the following attri-
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
| Availability | SUNWcsu |
at(1), crontab(1), sh(1), logadm(1M), queuedefs(4), sha-
A history of all actions taken by cron is stored in
/var/cron/log and possibly in /var/cron/olog.
Man(1) output converted with