My Journey with Automation Tool - Use of Cron

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My Struggle

Like the SSL certificate for penguingogo.com, it will normally expire after 90 days.

There is a time, I forget to renew the certificate and fail to access the https of website. That’s why a automation tool would be important for me.

Use of Cron

With a need of automation tool for running certain command or script in a fixed interval, Cron is introduced.

Cron is a powerful utility in Unix-based systems (like Linux) that allows users to schedule automated tasks, known as “cron jobs,” to run at specified intervals. It’s an essential tool for system administrators and developers who need to automate repetitive tasks, such as backups, updates, and maintenance scripts.

Key Features of Cron

  • Automation: Automate routine tasks to improve efficiency and reduce manual intervention.
  • Scheduling Flexibility: Schedule tasks to run at various intervals, from every minute to once a year.
  • User-Friendly: Simple syntax for specifying schedules, making it accessible for users of all skill levels.

How Cron Works

Cron uses a configuration file called the “crontab” (cron table) to manage scheduled tasks. Each entry in the crontab file specifies:

  • Time and Date: When the task should run (minute, hour, day of the month, month, day of the week).
  • Command: The actual command or script to be executed.

My Use Case

To use crontab for updating SSL certificate every 3 months.

Step 1

  • I created a shell script,updateCertificate.sh, in ~/scripts and included the required command:

      getssl -f penguingogo.com

Step 2

  • I use crontab -e to introduce tasks about running the script every 3 month at 2:30AM by cron. And the crontab entry inside crontab -e looks like:

      30 2 * */3 * ~/scripts/updateCertificate.sh
    • 30 2: Runs at 2:30 AM.
    • * * */3 *: Runs every 3rd month.
    • ~/scripts/updateCertificate.shh: The script to be executed.

    If you have your own time interval want to set, highly recommend to use https://crontab.guru/. It is a simple editor for cron schedule expressions.

Conclusion

With these few simple steps, now, I can be care-free about expiration of the ssl certificate! This method is also very useful for creating constant backup!