Informational

Example to run every 15th minute:

*/15 * * * *

Example to run on the 1st and the 15th of each month:

0 0 1,15 * 1

(minute) (hour) (day) (month) (day)

*          any value
,          value list separator
-          range of values
/          step values

crontab -a filename

Install filename as your crontab file. On many systems, this command is executed simply as crontab filename (i.e., without the -a option).

crontab -e

Edit your crontab file, or create one if it doesn't already exist.

crontab -l

Display your crontab file.

crontab -r

Remove your crontab file.

crontab -v

Display the last time you edited your crontab file. (This option is available on only a few systems.)

crontab -u user

Used in conjunction with other options, this option allows you to modify or view the crontab file of user. When available, only administrators can use this option.

You can monitor cron activity via /var/log/cron.