WHAT ARE CRON JOBS
The cron system in Linux is used to schedule jobs to run at specific times. The name was derived from the Greek word for time : Chronos. It was first released in 1975 and runs on several operating systems, not just Linux, but has been one of the reasons to make Linux so successful, in that housekeeping and other administrative jobs can easily be automated.
cPanel itself uses cron jobs for a host of things including:
• To run backups
• To clean up log files
• To update itself to the latest version of cPanel
• To ensure the operating system has all its latest updates applied
• To analyse log files and produce statistics and reports
• To perform various daily housekeeping tasks
Cron commands allow one to specify the minute, hour, day of the month, month and day of the week as parameters for when the job should be run. All of these can be wildcards, allowing for the repeated execution of jobs at regular minute, hour, day, week or monthly intervals. Also one can specify the minutes as */5 to run something every 5 minutes for example.
Cron commands can run anything that can be done on Linux, including running PHP scripts or even sending requests to websites.
Many PHP applications require housekeeping of their own to be done on at least a daily basis and when you install them they will ask you to add a cron command to ensure this is done. They are often used by applications for invoicing clients, sending reports via email or cleaning up old data.
For more details on how to add a cron job see our articles [How do I create and delete a cron job] and [how to set a cron job to use a specific php.ini file] and [Setting a cron job to run at a specific date and time]