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Cron Jobs

Simple, repetitive tasks figure a lot in the day-to-day lives of a web and database server admins. Time and again they are required to make backups or message users with updates.

So, just as a Windows system has its “scheduled tasks”, a Linux box offers an equivalent approach to dealing with these repeating day-to-day jobs, and it calls them cron (as in “chronology” or time) jobs. Since website management is no longer solely the responsibility of experienced admins, cron jobs have also entered the vocabulary of the average user taking care of their own website.

A cron job is a program that lets you schedule when particular tasks will be run. Our web hosting plans feature a Crontab Manager which can do this for whatever action you care to choose.

A cron job is an automatic daemon (which means a process that’s continuously running in the background). It allows for particular commands or collections of commands (scripts) to be run at certain intervals. You can use cron jobs for things like system admin commands, making backups, or actions that need to happen every day, like sending email updates. Another useful word in the vocabulary is ‘crontab’, which is short for ‘cron table’, a table which lists cron jobs.

Cron Job Management without SSH access

Back at the dawn of time (May 1975) when cron jobs were new, you had to use the server’s command line to set them up. There was no other way. As more and more people became involved with managing their sites, they needed to set up cron jobs themselves, but most hosting companies didn’t want to risk giving them SSH access due to security issues. So, it made more sense to add cron management to hosting control panels like Plesk or cPanel. Control panels let you set up cron jobs via an easy-to-use menu-driven interface.

Advanced Cron Jobs

If you are advanced, then you can decide when the cron will run using the “crontab” field. The numbers and the “*” symbol represent the precise time when the cron will be executed.

.—————- minute (0 – 59)
|  .————- hour (0 – 23)
|  |  .———- day of month (1 – 31)
|  |  |  .——- month (1 – 12)
|  |  |  |  .—- day of week (0 – 6) (Sunday=0 or 7)
|  |  |  |  |
*  *  *  *  *

Run once per year 0 0 1 1 *
Run once per month 0 0 1 * *
Run once per week 0 0 * * 0
Run once at midnight, every day 0 0 * * *
Run once per hour 0 * * * *