Mastering Scheduled Tasks: A Beginner's Guide to Crontab in Unix

Mastering Scheduled Tasks: A Beginner's Guide to Crontab in Unix

What is Crontab?

Crontab (CRON Table) is a file which contains the schedule of cron entries to be run and at specified times. Cron is the system process that will automatically perform tasks for you based on the schedule you set in the crontab. Each user on a system can have their own crontab file, and though these are files in a directory, they are not intended to be edited directly.

Basic Format of Crontab

Crontab entries have the following format:

Simple Example

Let's say you want to create a backup of all your user’s home directories every day at midnight. Your crontab entry would look like this:

0 0 * * * /usr/bin/tar -czf /backup/home-$(date +\%Y\%m\%d-\%H\%M).tar.gz /home/

Here’s what it does:

• 0 0 * * *: The schedule part tells cron to run this command at minute 0 of hour 0 of every day, which translates to midnight.
• /usr/bin/tar -czf /backup/home-$(date +\%Y\%m\%d-\%H\%M).tar.gz /home/: This is the command that will be run. It uses tar to create a compressed archive of the /home directory, and the archive file name includes the current date and time.

Managing Crontab

To edit or create your personal crontab file, you can use the command:

crontab -e

To list your crontab file:

crontab -l

To remove your crontab file:

crontab -r

This should give you a fundamental understanding of how to use crontab for scheduling tasks on a Unix-based system. Always make sure to specify the full path to any scripts or commands in your crontab entries to avoid any issues due to environmental path variables not being loaded for cron jobs.