An Overview of Crontab in Linux [The Ultimate Guide]

Cron originated from the Greek word ‘Chronos’(time) and empowers Unix or Linux-based users to execute commands at predefined specific times. Crontab or Cron Table allows task schedulers, cron to perform its commands. Let’s have an overview of Crontab in Linux to get familiarized with automation!

What is Crontab in Linux?

Crontab is the abbreviation for Cron Table. Basically, it is a set of commands which empowers the users to run their desired operations at predefined specific times. Moreover, it also represents the command that is utilized to modify the scheduling system. So, in short, crontab is not only the schedule but also the editor to maintain the schedule.

Significance of Cronjob in Linux?

As cronjob empowers users to schedule tasks it opens the door to automation in several aspects:

  • Computerized system maintenance
  • Automating disk space monitoring
  • Scheduled backups
  • Automated notifications

Crontab Syntax & Operators in Linux

Syntax of Crontab in Linux

Crontab syntax is made of five fields and commands which are to be executed. The five fields are a must and they can be separated by one or more spaces.

Syntax of crontab

Disclaimer: You cannot leave any field blank and their order must be followed exactly.

Some Essential Operators of Crontab in Linux

To set specific times for your cronjobs you must learn the use of the following essential crontab operators.

  • Asterisk (🞸), This character is used to define all possible values. For example, if used in the minute field it will represent every minute.[1,2,3,4,5,……,58,59].
  • Comma(,), This character can be used to specify a list[5,6,7]
  • Hyphen(-), This can be used to specify a range[1-9]
  • Separator(/), You can run operations after every specific duration by utilizing this character (*/time_step)
Syntax a b c d e Tasks




Day of month




Day of week


commands or any scripts.
Scenario */5 7 🞸 6,7 0-4 commands to be executed.
Interpretation Every 5 mins At hour 7 Every day of a month June, July Sunday to Thursday Completes the assigned job.

Some Distinct Useful Strings of Crontab in Linux

You can use some distinctive strings as an alternative to the specific syntax configurations to schedule tasks. For this, you have to use the ‘@’ symbol followed by some specific terms.

  • @hourly, This will execute the tasks for every hour.
  • @daily or @midnight, Performs the job at midnight of every day.
  • @weekly, Completes the task only one time at midnight on Sunday.
  • @monthly, Cron performs the job on the 1st day of every month.
  • @yearly, This will run the operations on 1st January of every year.
  • @reboot, Completes the task one time at every start-up.

Basics of Crontab in Linux

Selecting Editor for Crontab

In Ubuntu, for the first time when you run crontab -e to modify the crontab, the terminal tells you to select 1 editor for the purpose. In this article, I am going to select nano.

Selecting editor for crontab in Linux for the first time.

After pressing 1 and then hitting ENTER will set the nano editor as crontab editor. However, if you’ve already been using another editor or you want to change it, you can do it easily by running the following command.


Changing current crontab editor.

Modifying Crontab

You can modify or add your desired crontab jobs by executing the crontab -e(e for edit) command

crontab -e

This will open the crontab editor in nano where you can put your tasks.

Crontab in nano editor.

If no task is added after exiting the editor it will just print that no modification made.

No modification was made in crontab.

However, if you add one it will start installing the crontab.

Installing the new crontab after making modifications.

Listing Crontab

By running the following command you’ll be able to view modifications in the crontab on your terminal.

crontab -l

Listing the crontabs on the machine of that user.

Removing Crontab

You can remove your crontab modifications by running the below command.

crontab -r

Removing all the cronjobs.

Modifying Crontab of Other Users

By running the following command you can modify cronjobs for another user from your terminal.

crontab -u INSERT_USERNAME -e

Modifying Crontab As a Root User

You can modify the cronjobs of the root user. For able to do this you have to use sudo as a prefix command to crontab -e.

sudo crontab -e

Modifying cronjobs of the root user.

Examples of Crontab in Linux

Currently, you’ve learned about the syntax, operators, and modifications of the crontab editor. To make things more clear about crontab let’s go through the following examples. Before moving on to the examples let’s refresh the syntax of crontab in Linux.

Syntax a b c d e Tasks




Day of month




Day of week


commands or any scripts.

And finally, let’s assume that we have a script named “backup” in our home directory which will back up the contents of our desktop.

Sample Commands Interpretations
* * * * * /home/user1/backup Completes the task of backup every minute
10 * * * * /home/user1/backup Cron Completes the task of backup every 10th min of every hour.
30 6 * * * /home/user1/backup Performs the task of backup every day at 6:30 AM.
0 0 1 * * /home/user1/backup Cron performs the task of backup at midnight on 1st day of every month.
*/30 * * * 1-5 /home/user1/backup Executes the task of backup at intervals of every 30 minutes from Monday to Friday.
* */6 * jan,dec * /home/user1/backup Cron Completes the task of backup at intervals of every 6 hours for the month of January and February.
* * * * * /home/user1/backup; /home/user1/script2 Completes two tasks every minute using a sole cron.
@hourly /home/user1/backup Performs the task once every hour.
@yearly /home/user1/backup Cron executes the task only one time a week on Sunday at midnight.
@reboot /home/user1/script2 Completes the task every once of the startup.


Scheduling tasks is a useful option if you don’t want to perform redundant things yourself. Crontab can be viewed as a special tool to perform this task of scheduling or automation. All you need to master crontab in Linux is to learn the precise syntax and formatting of crontab and then implement it with your creative vision.

Similar Readings

Rate this post
Md. Ashakul Islam Sowad

Hi, I am Md. Ashakul Islam Sowad from Dhaka, Bangladesh. I have completed my undergraduate degree in Biomedical Engineering from the Bangladesh University of Engineering and Technology (BUET). I love to watch football and play video games in my free time. Here, I am working as a Linux Content Developer Executive. Furthermore, as a Linux enthusiast, I am always learning new things about Linux-based systems and I’ll be sharing them here. Read Full Bio

Leave a Comment