Crontab command allows you to schedule the execution of tasks on a regular basis.

For instance, you can schedule the execution of shell scripts on a flexible schedule instead of manually invoking those shell scripts.

How Crontab works

Here are the points to keep in mind:

1. Crontab tasks do not inherit the environment of a specific user, which means that you must ensure that all required environment variables are set properly (such as invoking a script that contains those variables).
2. You can schedule a task to run based on the following:

an hourly, daily, or weekly basis a specific day of the month a specific month or year

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The following command displays the currently scheduled jobs for your machine:

$ sudo crontab

In other ways, you can use crontab -l to list all the jobs present.

$ sudo crontab -l

Edit

You need to be either the root user or use sudo in order to modify crontab (in the /usr/bin directory) with the following command:

$ sudo crontab -e

Replace

The following command replaces the current set of jobs with the jobs in the file crontab.new:

$ crontab -r < crontab.new

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