Blog / What are Crons? How do they work?

What are Crons? How do they work?

by SW Team

Crons, also known as "Cron Jobs", are an essential function in Unix and Linux operating systems that allow tasks to be scheduled and automated. These tasks can be executed periodically according to a pre-established schedule. Crons are commands or scripts that are configured to run at specific times, whether every minute, hour, day, week or month, depending on the user's needs.

The word "cron" comes from "chronos", the Greek word that means "time". Crons allow users to harness the power of automation to perform repetitive activities without constant manual intervention. From performing backups to cleaning up temporary files to updating information on websites, crons are a valuable tool for improving the efficiency of system and server administration.

How do the Crons work?

Crons work by using a special file known as a "cron table". This file contains a list of commands and the corresponding schedules to execute them at specific times. When you set up a cron, you specify the interval at which you want the task should to run, whether it is every minute, hour, day, week or month.

The operating system constantly checks this cron table to see if there are any tasks that need to be run at that time. And when the scheduled time for a particular task arrives, the system executes the command or script associated with that task. This is done automatically without human intervention, ensuring accurate and timely execution.

They can be programmed to perform a wide range of tasks, from simple commands to more complex scripts. This allows users to automate repetitive processes, such as generating reports, updating databases or managing files, without the need for manual intervention.

Below is an example of a quick setup guide for Crons;

.--------------- minute (0 - 59)
|  .------------ hour (0 - 23)
|  |  .--------- day of the month (1 - 31)
|  |  |  .------ month (1 - 12)
|  |  |  |  .--- day of the week (0 - 6) (Sunday to Saturday;  7 is also Sunday on some systems)
|  |  |  |  |
*  *  *  *  *  <command to execute>

Also, here is an example of a Cron that runs the /home/user/ script every 5 minutes;

*/5 * * * *  /home/user/

If you click on this link, you can also see how to create and manage Crons using our control panel, SWPanel.

Advantages of using Crons

The use of Crons in scheduling and task automation offers many significant advantages that have a positive impact on the management of systems and servers. Some of these advantages are:

  • Efficient automation: One of the biggest advantages of Crons is its ability to automate tasks efficiently and accurately. By scheduling tasks to run at specific times, Crons eliminates the need for manual intervention.

  • Precise planning: It allows detailed scheduling of when tasks should be performed. This is particularly useful in environments where server performance is critical. For example, resource-intensive tasks can be scheduled to run at off-peak times to avoid negatively impacting the user experience.

  • Reduction of errors: Manual execution of repetitive tasks carries the risk of error. By performing tasks automatically and consistently, Crons reduce the possibility of human error. This is particularly important for critical tasks, such as database management or backups, where errors can have serious consequences.

  • Flexibility in administration: It offers great flexibility in managing systems and servers. It can be configured to perform a wide range of tasks, from the simplest to the most complex. This means it can be tailored to the specific needs of each system and adapted to the unique requirements of the infrastructure and applications.

  • Increase in productivity: It allows you to focus on more strategic and higher-value activities, such as developing new features, solving more complex problems or long-term planning. Ultimately, this increases team productivity.

Examples of common tasks with Crons

Task 1: Periodic Backups

One of the most common uses of Crons is to perform regular, automatic backups. For example, on a website, a Cron can be scheduled to perform a daily backup of the database and important files. This task ensures that, in the event of any problems or data loss, you will have an updated version to quickly restore your system.

Task 2: Cleaning Up Temporary Files

It can also be used to keep the system clean and organised by automatically deleting temporary files or logs that are no longer needed. Setting up a Cron Job to periodically clean up these files will help prevent storage clutter and improve overall system performance.

Task 3: Updating Website Content

If you run a website with content that needs to be updated regularly, Crons can be a great help. For example, if you have a blog and you want to publish new articles every Thursday at 10am, you can schedule a Cron to automatically run a script that publishes the article at the specified time.

Task 4: Sending Automated Emails

If you have a list of subscribers and want to send out a weekly newsletter, you can set up a Cron to automatically send the newsletter at a specific time. This ensures that subscribers receive the email at the scheduled time, without having to send it manually.

Task 5: Updating Software and Patches

Keeping software and systems updated is essential for security and performance. With Crons, updates and patches can be scheduled to run automatically at times when there is less server activity, minimising the impact on users.

Tips to avoid problems with Crons

Although Crons are a valuable tool for automating tasks, it is important to use them with caution and consider certain aspects to avoid potential problems. Here are some tips to ensure a smooth and effective use:

  • Detailed activity log: Activating activity logs is essential to work with Crons. By keeping a detailed record of executions, you can track any problems that occur and quickly diagnose errors. Logs also allow you to check that tasks are running as planned and that they are having the expected effect on the system.

  • Pre-testing in a development framework: Before implementing new Crons in a production environment, it is recommended that you perform extensive testing in a development or test environment. This will allow you to verify that the commands and scripts work correctly, and do not cause unexpected problems in the system. Testing is also an opportunity to adjust time intervals and ensure that tasks run efficiently.

  • Perform backups before implementing changes: Before adding, changing or deleting Crons, make a full backup of the system and the existing Crons table. This will allow you to undo changes if something goes wrong during configuration or task execution. Backups are an important safeguard against data loss or unexpected downtime.

  • Constant monitoring: Although Crons are designed to run automatically, it is important to monitor scheduled tasks at all times. This allows you to identify problems early and take corrective action. Use monitoring tools to receive alerts if a task does not run as planned or if an error occurs.


Crons are an essential tool for the efficient and scheduled automation of tasks on systems and servers. Their ability to execute commands and scripts on a pre-set schedule provides significant advantages such as the elimination of repetitive manual tasks, accurate scheduling and increased productivity. However, it is important to take a cautious approach to the configuration and use of Crons, following tips such as enabling activity logs, pre-testing and constant monitoring. With a balanced focus on automation and security, Crons can optimise technology management and simplify system administration, allowing teams to focus on strategic tasks with higher value-add.

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