How to setup cron jobs in Ubuntu
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
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