Creating a Cron Task in Ubuntu 16.04.
A Linux tool used for scheduling tasks in a server.
Cron jobs are an incredibly useful Linux tool aimed at saving you time by scheduling tasks within your server. A programmed cron task will execute commands within a script by the minute, day, week or month. They can be scheduled to do many tasks including backing up your server’s files nightly, updating inventory orders in a database or even compressing files for migrating.
Ubuntu 16.04 LTS server
Setting Up a Website Backup through Cron
Step 1: Update your server. As a best practice, we will update and upgrade our server with the following command.
apt-get update && apt-get upgrade
Step 2: Verify if the cron package is installed.
dpkg -l cronOur example output let’s us know that the cron package is installed, along with its version:
||/ Name Version Architecture Description
ii cron 3.0pl1-128ubuntu2 amd64 process scheduling daemon
Install cron package if necessary.
sudo apt-get install cron
Ensure that the cron service is running with the following command:
systemctl status cronExample Output:
* cron.service - Regular background program processing daemon
Loaded: loaded (/lib/systemd/system/cron.service; enabled; vendor preset: enabled)
Active: active (running) since Sat 2020-05-22 02:53:20 EDT; 5 days ago
Step 3: Configure the cron job. When you are logged in as your user, you are creating a cron job under that user. Creating a cron jobs owner is helpful when to know who is in charge of the cron as well as how to alter the cron job in the future.
user1@host2:~$ crontab -e
no crontab for user1 - using an empty one
Select an editor. To change later, run 'select-editor'.
Choose 1-3 : 2
In this file, you’ll see # signs followed by the direction on how to use the file. Allow us a minute to explain the syntax needed to create a cron task.
# Example of job definition:
# .---------------- minute (0 - 59)
# | .------------- hour (0 - 23)
# | | .---------- day of month (1 - 31)
# | | | .------- month (1 - 12) OR jan,feb,mar,apr ...
# | | | | .---- day of week (0 - 6) (Sunday=0 or 7) OR sun,mon,tue,wed,thu,fri,sat
# | | | | |
# * * * * * user-name command to be executed
Each set of digits designates the time for that section and follows the time set in your server. The first set represents minutes, the next set hours, the next set day of the month and so on. You may be asking yourself what the asterisk mean. They represent every or all value for that set. So, if you put an asterisk on the month column, you’ll be telling the system to perform the tasks every month.
After the digits section is the /bin/sh and the type of file that should be executed, lastly, the final column assigns the command of which to run.
Let’s say you want to backup your website files daily. Our example uses 4 am since server traffic is low during this time. Take note of the .sh extension, indicating a bash script. Use the appropriate extension for your script. Be sure to save the script when exiting with :wq
After altering the /path/to/script/backup-script.sh path to match the location of your script, set the command in a new line, below the hashtag (#), like so:
# m h dom mon dow command
0 4 * * * /bin/sh /path/to/script/backup-script.sh
Step 4: Place Script in Path. Most importantly is the creation and placement of your script. With our example script we are creating a backup that will compress files and directories, indicated by the /SOURCE/DIRECTORY/. The /SOURCE/DIRECTORY/ needs to be alter to the directory and files you wish to save (sometimes a website’s default directory path is /var/www/html), while the /DESTINATION/DIRECTORY/file.zip indicates where the compressed backup are stored. We will name the script backup-script.sh, and afterwards, we will create the script in the location of /path/to/script/backup-script.sh.
zip -9pr /DESTINATION/DIRECTORY/file.zip /SOURCE/DIRECTORY/
Set execute permissions this allows the system permission to run the script.
chmod +x backup-script.sh
When the time of execution has passed, check your /DESTINATION/DIRECTORY/ to see file.zip.
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