cron.md

Syntax explained

https://en.wikipedia.org/wiki/Cron

There may also be another field at beginning for second.

 # ┌───────────── min (0 - 59)
 # │ ┌────────────── hour (0 - 23)
 # │ │ ┌─────────────── day of month (1 - 31)
 # │ │ │ ┌──────────────── month (1 - 12)
 # │ │ │ │ ┌───────────────── day of week (0 - 6) (0 to 6 are Sunday to
 # │ │ │ │ │                  Saturday, or use names; 7 is also Sunday)
 # │ │ │ │ │
 # │ │ │ │ │
 # * * * * *  command to execute

Examples:

# @hourly at beginning of hour
0 * * * *

# @yearly at midnight on Jan. 1
0 0 1 1 *

You can think of * as meaning all values.

Schedule a cron job

crontab -e

See http://www.cyberciti.biz/faq/how-do-i-add-jobs-to-cron-under-linux-or-unix-oses/. The crontab is stored in /var/spool/cron/, but is not meant to be edited by hand. See http://askubuntu.com/questions/216692/where-is-the-user-crontab-stored. To see recent cron job runs, run:

grep <script_name> /var/log/cron