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How to Setup Cron Job on Linux

How to Setup Cron Job on Linux

Overview

Cron is Linux most useful tools which allow running automated commands at specific date & time. This is developer favourite because it helps to set up the task-specific script in the background which will run on defined time. So In this post, we will learn how to a setup cron job using your shell user.

Prerequisites

  • Linux System where you setup cron
  • A command line or terminal window for add/edit/delete/list cron
  • A user account with root or sudo privileges

Cron Syntax

The command for view the existing cron

crontab -l

The command for creating and editing cron jobs

crontab -e

The standard form for a crontab line is as follows:

* * * * * /directory/command output

Explanation of above cron syntax:

  • 1 *: Minutes range: 0 - 59
  • 2 *: Hours range: 0 - 23
  • 3 *: Days range: 0 - 31
  • 4 *: Months range: 0 - 12
  • 5 *: Days of the week range: 0 - 7. Starting from Monday, 0 or 7 represents Sunday
  • /directory/command - specifies the location and script you want to run
  • output - it is optional and it defines how the system notifies the user of the job completion

Below are a few basic examples to get an idea of how it works.

Run once an hour (every hour at minute zero)

0 * * * * /var/www/html/cron-job mail.php >/dev/null 2>&1

Run at every 2nd minute

*/2 * * * * /var/www/html/cron-job mail.php >/dev/null 2>&1

Run at minute 30 means run at every hour at 30 minutes

30 * * * * /var/www/html/cron-job mail.php >/dev/null 2>&1

Run at every 12th hour

0 */12 * * * /var/www/html/cron-job mail.php >/dev/null 2>&1

Run once a day (every day at midnight and minute zero)

0 0 * * * /var/www/html/cron-job mail.php

Run once a month (on the first day of every month at midnight and minute zero)

0 0 1 * * /var/www/html/cron-job mail.php

Run once a year (on the first day of the first month every year at midnight and minute zero)

0 0 1 1 * /var/www/html/cron-job mail.php

Run at every Sunday

0 0 * * SUN /var/www/html/cron-job mail.php

Set up a crontab

Open you SSH into the server and edit the crontab

crontab -e

the crontab default editor is vi editors. So in vi editors below are the step to set up the crontab

  • press ESC.
  • press I (for "insert") to begin editing the file.
  • paste the cron command in the file.
  • Press ESC again to exit editing mode.
  • type:wq to save (w - write) and exit (q - quit) the file.

You can add multiple cron jobs. just add each corn command in a new line.

Conclusion

This is a simple post about how to set up cron jobs. I hope you like this article In next article we learn how to setup the node cron.

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