Linux commands: crontab

A quick guide to the `crontab` command, used to schedule cron jobs

Cron jobs are jobs that are scheduled to run at specific intervals. You might have a command perform something every hour, or every day, or every 2 weeks. Or on weekends. They are very powerful, especially on servers to perform maintenance and automations.

The crontab command is the entry point to work with cron jobs.

The first thing you can do is to explore which cron jobs are defined by you:

crontab -l

You might have none, like me:

Run

crontab -e

to edit the cron jobs, and add new ones.

By default this opens with the default editor, which is usually vim. I like nano more, you can use this line to use a different editor:

EDITOR=nano crontab -e

Now you can add one line for each cron job.

The syntax to define cron jobs is kind of scary. This is why I usually use a website to help me generate it without errors: https://crontab-generator.org/

You pick a time interval for the cron job, and you type the command to execute.

I chose to run a script located in /Users/flavio/test.sh every 12 hours. This is the crontab line I need to run:

* */12 * * * /Users/flavio/test.sh >/dev/null 2>&1

I run crontab -e:

EDITOR=nano crontab -e

and I add that line, then I press ctrl-X and press y to save.

If all goes well, the cron job is set up:

Once this is done, you can see the list of active cron jobs by running:

crontab -l

You can remove a cron job running crontab -e again, removing the line and exiting the editor:

The crontab command works on Linux, macOS, WSL, and anywhere you have a UNIX environment