cron job asterisk meaning

Question

I'm a little bit confused about cron job parameters. I'm using bitnami magento installation on amazon azure. I found that if I want to run cron tasks I have to configure cron job

and there is this line

* * * * *  su daemon -c "/bin/sh /opt/bitnami/apps/magento/htdocs/cron.sh"

and I do not understand how frequently I will run ? As I understant setting my own cron task I will also have to use asterisk to set frequency. Can anyone explain how to understand this asterisk convention ?

Thanks in advance.

Answer 1

* = always. It is a wildcard for every part of the cron schedule expression.

So * * * * * means every minute of every hour of every day of every month and every day of the week.

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

The nice drawing above is provided by wikipedia

An other example:

0 * * * * -this means the cron will run always when the minutes are 0 (so hourly)
0 1 * * * - this means the cron will run always at 1 o'clock.
* 1 * * * - this means the cron will run each minute when the hour is 1. So 1:00, 1:01, ...1:59.

Answer 2

Minutes [0-59]
|   Hours [0-23]
|   |   Days [1-31]
|   |   |   Months [1-12]
|   |   |   |   Days of the Week [Numeric, 0-6]
|   |   |   |   |
*   *   *   *   *