Scheduling Jobs in Linux with CRON(CRONTAB)

CRONTAB is a very useful utility in Linux to schedule your day to day jobs.CRONTAB or CRON simply runs commands or scripts at a scheduled time.

In this article, we will learn scheduling Jobs in Linux with CRONTAB. We will take examples to understand it.

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 CRONTAB Commands

Below are the important crontab commands that we must know.

       1.Add a new Job in CRONTAB

        $ crontab -e

This command will open an empty file. You need to put your commands or scripts here to run your command or script automatically at a particular interval of time.

      2. Display all Scheduled Jobs in CRONTAB

          $ crontab -l

This command will display all scheduled jobs.

• CRONTAB Format

Below is the format of CRONTAB or CRON that we put in CRONTAB – I command.

          * * * * * /path/to/script.sh

            Here definition of * * * * *  are as follows:

min	hour	day of month	month of year	day of week
0-59	0-23	1-31	1-12	0-6

Examples :

1.  A Script is scheduled to run 5:10 AM every day.

 

2.  A Script is scheduled to run 5:10 AM to 5:20 AM every day.

 

3.  A script is scheduled to run every 5 min.

 

4.  A script is scheduled to run at 11 AM on 10th of March

 

5.  A script is scheduled to run at 1 AM every Saturday.

 

6. A command to restart MySQL service at 10 am every day.

    3.Remove current Job in CRONTAB
      $ crontab -r

     4.Prompt before removing a CRONTAB.

           $ crontab -ir

     5.Add and display CRON for a particular user.

Use “- u username” after crontab -l or crontab -e to display or edit crontab for a particular user.

        $crontab – l -u username

        $crontab -e -u username

     6.List name of the users who have CRONTAB jobs.

      $ ll /var/spool/cron

This article ends here.

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