Cron Job: Complete Beginner's Guide

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Cron Job: Complete Beginner's Guide 2021
Doing the same task over and over again can be quite a chore. Scheduling cron jobs allows users to automate tasks on VPS hosting or any Unix-like operating system. This saves valuable time, allowing users to focus on other essential tasks.

In this complete beginner's guide, you will learn the basics of cron jobs, including their types, syntax, special strings, and permissions. By the end of this article, you will be able to use cron jobs to schedule tasks more efficiently.

Let's get started.

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What is a Cron Job?
Cron is a utility that allows users to enter commands to schedule tasks repeatedly at a specific time. Tasks scheduled in cron are called cron jobs . Users can determine the type of task they want to denmark phone number data and when it should be run.

Cron is a daemon , a background process that performs non-interactive work. In Windows, you may be familiar with background processes such as services that work similarly to the cron daemon.

A daemon is always idle, waiting for a command to perform a particular task. The command can be issued on any computer on the network.

A cron file is a simple text file that contains commands to be run periodically at a specific time. The default system cron table or crontab configuration file is /etc/crontab , located in the crontab directory /etc/cron.*/ .

Only system administrators can modify the system crontab file. However, Unix-like operating systems support multiple administrators. Anyone can create a crontab file and write commands to run jobs whenever they want.

With cron jobs, users can automate system maintenance, monitor disk space, and schedule backups. Because of their nature, cron jobs are great for computers that run 24/7, such as servers .

While cron jobs are primarily used by system administrators, they can also be useful for web developers.

For example, as a website administrator, you can set up a cron job to automatically back up your site every day at midnight, another to check for broken links every Monday at midnight, and a third to clear the site’s cache every Friday at noon.

However, like any other program, cron has some limitations that you should consider before using it:

The shortest interval between jobs is 60 seconds . With cron, you will not be able to repeat a job every 59 seconds or less.
Centralized on one computer. Cron jobs cannot be distributed across multiple computers on a network. So if the computer running cron crashes, scheduled tasks will not run and lost jobs can only be run manually.
No automatic retry mechanism . Cron is designed to run at strictly specified times. If a task fails, it will not run again until the next scheduled time. This makes cron unsuitable for incremental tasks.
With these limitations, cron is a great solution for simple tasks that run at a specific time with regular intervals of at least 60 seconds.

If you want to schedule a one-off job for later, you may want to use another method .

Basic Cron Job Operations
This tutorial will show you how to schedule cron jobs by entering commands into a shell program like Bash on Linux or another Unix-like operating system.

VPS hosting usually runs on a Linux-based operating system. Therefore, learning how to schedule cron jobs will significantly increase the efficiency of your work as a VPS administrator. You can access the command line for VPS via SSH .

Before proceeding with the basic operations of cron scheduling, it is essential to know the different cron job configuration files:

The system crontab. Use it to schedule essential system-wide jobs that can only be modified with root privileges.
The user's crontab. This file allows users to create and modify cron jobs that apply only at the user level.