How to Set Up Cron Job on CentOS 7

Set Up Cron Job on CentOS

CronJob is the task scheduler in Linux which schedules the task at a specific time or schedules task to repeat itself after a specific time. In this tutorial, you are going to learn how to set up a Cron Job on CentOS by using the crontab command.

Prerequisites

Before you start to set up a Crontab on CentOS. You must have a non-root user account on your server with sudo privileges.

Open crontab with a text editor

To open crontab with text editor enter following command

crontab -e

Once you enter the above command you will be asked to choose a text editor. Choose nano if you are first time editing or go with your choice.

In the crontab, the m h dom mon dow user header has the following meaning

* m = The minute when the cron job will run. (0 to 59)
* h = A integer determining the hour when the tasks will run. (0 to 23)
* dom = Day of the Month when the cron job will run. (1 to 31).
* mon = The month when the cron job will run. (1 to 12)
* dow = Day of the Week from 0-6 with Sunday at 0. (0 to 6)
* user = The User under which the cron will run.
* command = The Linux command you wish to execute.

Asterisks (*) on the crontab timings

Here in setting up cronjob asterisks (*) is used widely. What it means is that if you put * for m (minute) then it will run that command every minute.

Basic Examples of Cron Jobs

Cron that runs every minute

* * * * * [user] [command]

Cron that runs 10th minute of the hour like 12:10, 01:10, 02:10, etc.

10 * * * * [user] [command]

Cron that runs 30th minute of the hour like 12:30, 01:30, 02:30, etc.

30 * * * * [user] [command]

Cron that runs every hour (when the minute will become zero)

0 * * * * [user] [command]

Cron that runs at midnight

0 0 * * * [user] [command]

Cron that runs at 8 am

0 8 * * * [user] [command]

Cron that runs a PHP script

 * * * * * root /usr/bin/php /var/www/html/project/test.php

Advanced examples of crontab

Using commas in crontab:
The following command will execute at 8:45 am on the 15th day of January, March, July, December.

45 8 15 Jan,Mar,Jul,Dec * [user] [command]

Using division operator in centos crontab:
As the minute is divided by 10. the following command will execute at every 0,10,20,30,40,50th minute of the hour (when the minute is divisible by 10).

*/10 * * * * [user] [command]

Dashes in crontab:
The following crontab will run from 15th to 20th day of every month. As the dash represents the range.

0 0 15-20 * * [user] [command]

Conclusion

Here you have successfully learned how to set up Cron job in CentOS. if you have any queries regarding this, please comment below.