There are a few inherent functions included with Magento that can be run periodically, including:

Some third-party modules also include scheduled tasks, such as Google Product feeds. The frequency of most of these can be configured in your Magento backend. For those that aren't, you can find the crontab-style setting for each in the config.xml file of each module.

For example, the following is the cron schedule for the function that sends out scheduled newsletters, from app/code/Mage/Newsletter/etc/config.xml:

    <crontab>
        <jobs>
            <newsletter_send_all>
                <schedule><cron_expr>*/5 * * * *</cron_expr></schedule>
                <run><model>newsletter/observer::scheduledSend</model></run>
            </newsletter_send_all>
        </jobs>
    </crontab>

According to this crontab, Magento looks every 5 minutes to see if any newsletters need to be sent out.

Many of Magentos core modules contain crontab scripts, although some are commented out. The following is a list of Magento Community 1.5 crontabs I have found within Magento, indicating for each whether the script is active or not. To make a script active, simply remove the comment tags surrounding the <crontab> code in the appropriate config.xml file.

For your staging environment, you may want to keep cron jobs from running automatically. Rather, you may wish to have Magento run through its list of scheduled tasks at your command so you can watch for any problems or errors.

A wrinkle in Magento 2.0 is that there's no longer a cron.php, so Magento's cron can no longer be triggered from the command line (manually).

To manually run any scheduled jobs, access the magento file found in your site's root folder from the terminal and use the following command:

php <path to magento root>/bin/magento cron:run

For your production server, you'll want cron jobs to run as scheduled around the clock. To do this, you have to create a cronjob for your server, telling it how often to trigger Magento's cron tasks. For most servers — Unix and Linux — the cron program operates as a continuous daemon, waiting to take some action according to any programmed crontabs. In this case, we want to have the magento binary (also in our Magento root folder) run by the server every few minutes or so.

The most straightforward way to schedule a cron job is to do so from the command line. Start by opening up a command prompt as the root user and typing in the following command:

crontab –e

This command will take you to a screen where you can add entries to schedule the cron. To automate the Magento cron, you'll want to add entries that look like this:

You can schedule crons to run every X number of minutes, hours, days, or months. You can schedule them to run only during certain times of the day, days of the week, or months of the year. Cron is an amazingly flexible system. The following screenshot shows the logic for scheduling crons:

This can be a bit obtuse to understand, though; if you want a quick way to sort out timing for a cron job, you can visit one of the many crontab generating websites. One example is http://crontab-generator.org/. As you can see, this site provides assistance and makes it a bit easier to generate the desired schedule:

The Magento binary does a number of things when your server cron job runs:

The parameters that control this behavior are configured in your Magento backend:

Each field in this panel controls the timing actions of the cron script, as follows:

There remains considerable debate among bloggers on what values are ideal for this configuration. However, from my observations, there are some principles I follow when configuring Magento cron jobs.

Creating compatible settings

Once you have modified any crontabs to match your system cron job frequency, you should now configure the Store | Configuration | Advanced | Cron (Scheduled Tasks) panel:

• Use the same number of minutes as your system cron job frequency for Generate Schedules Every.
• Use the same value for Schedule Ahead For. In this way, you are capturing all the upcoming cron jobs Magento intends before your next system cron runs.
• Use the same value for Missed If Not Run Within to run any scheduled tasks that did not run during the last system cron.
• Use the same value for History Cleanup Every. You can use a larger interval if you wish, as this is not a critical function to running the necessary cron jobs for your store.
• For Success History Lifetime and Failure History Lifetime, you can use whatever settings you feel are most important. Generally, when launching a new Magento store, I set the Failure History Lifetime for a long time (as much as 3 days, or 4320 minutes) so that if something seems amiss, I can go into the cron_schedule database table and see if there are any failure messages that can help me diagnose the problem. In fact, even if your store is running smoothly, keeping this number large should not grow your database, as there will be no failure messages to record.

So, for example, if I set my system cron job to run every 15 minutes, my Cron (Scheduled Tasks) panel might look like this: