Cron is one of the most useful utilities in FreeBSD. Cron is application that running in background that checks file /etc/crontab constantly, it is usually used for automatic commands execution. Using cron and this crontab file you can also start any service you want automatically or scheduled.
1. to change crontab or edit crontab file (using ee or vi)
ee /etc/crontab
you will see lines like this
PATH=/etc:/bin:/sbin:/usr/bin:/usr/sbin
#
#minute hour mday month wday who command
#
*/5 * * * * root /usr/libexec/atrun
* */2 * * * root sh /root/download.sh
by reading it you will understand that you just need to edit or add lines and commands, like the example given. for example, i want to automatically erase files in directory every 30 days that is on 1st day of each month. i can add this line
#minute hour mday month wday who command
0 0 1 * * root rm -r /home/administrator/file
2. Save it and restart cron
to restart cron on FreeBSD
simply type this command
/etc/rc.d/cron restart
to restart cron on linux, ubuntu
type this command
/etc/rc.d/cron restart
this is the time reference to edit crontab
min hour mday month wday Execution time
30 0 1 1,6,12 * 00:30 Hrs on 1st of Jan, June & Dec.
0 20 * 10 1-5 8.00 PM every weekday (Mon-Fri) only in Oct.
0 0 1,10 * * midnight on 1st & 10th of month
5,10 0 10 * 1 At 12.05,12.10 every Monday & on 10th of every month