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How to setup cron jobs in Ubuntu

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The Cron software utility is a time-based job scheduler in Unix-like operating systems. Cron allows Linux and Unix users to run commands or scripts at a given time and date. Once can schedule scripts to be executed periodically. It is usually used for system admin jobs such as backups or cleaning/tmp/ directories and more. The following steps to be followed to set up a cron job in Ubuntu:
  • Connect to server and update the system: Before begin with setting up crontab connect the server and update the system software to the latest version available. We can do this by using below command:
    #apt-get update && #apt-get upgrade
  • Check if cron package is installed: To check if cron is installed, run the following command –
    #dpkg -l cron 
  • If cron is not installed, install the cron package on Ubuntu: One can Install the cron package with package Manager using the following command-
    #apt-get install cron
  • Verify if cron service is running: To check whether the cron service is running on the system, we can use the following command-
    #systemctl status cron
  • Configure cron job on ubuntu: In order to set up cron jobs, one needs to modify the /etc/crontab file which can be done by only root user. You can edit the crontab file with following text editor. Example:
    #nano /etc/crontab
Before we take example of cron tab execution let’s understand the common syntax of cron tab: Syntax:
* * * * * /path/to/command arg1 arg2
OR
* * * * * /root/backup.sh
In the syntax first * stand for representing minutes [0-59]. Second * stands for representing hour[0-23]. Third * stand for representing day [0-31]. Fourth star stands for representing month[0-12]. Fifth * stand for representing day of the week[0-7].   After all step for installation of cron tab and understanding common syntax, let’s execute a cron tab with suitable example. Example #1: If we want to schedule a backup on first day of each month at 9 PM, the following command performs this operation.
#crontab -e //install your cron job by running this command.
// Append the following entry.

0 9 1 * * /path/to/script/backup-script.sh
  Example #2: Set up and run php script as cron job to run script every day at 10 AM.
#crontab -e //add cron job

// Append the following entry.
0 10 * * * /path/to/myphpscript.php
Following options are available in crontab: crontab -l : List the all your cron jobs. crontab -r : Delete the current cron jobs. For more information about cron, one can check the manual pages using:
man cron
man crontab 

Last Updated : 27 Feb, 2020
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