Show all on the tasks

crontab -l

Add/Edit tasks, after you exit from the editor, the modified crontab will be installed automatically.

crontab -e

How to schedule the tasks?

# For details see man 4 crontabs

# Example of job definition:
# .---------------- minute (0 - 59)
# |  .------------- hour (0 - 23)
# |  |  .---------- day of month (1 - 31)
# |  |  |  .------- month (1 - 12) OR jan,feb,mar,apr ...
# |  |  |  |  .---- day of week (0 - 6) (Sunday=0 or 7) OR sun,mon,tue,wed,thu,fri,sat
# |  |  |  |  |
# *  *  *  *  *  command to be executed
  10 13 *  *  *  php PATH/my_script.php 

This example will run everyday at 1.10pm.

References: http://www.thegeekstuff.com/2009/06/15-practical-crontab-examples/

Enjoy!