The software utility cron (or cron job) is a time-based job scheduler in Unix -like operating systems.

Crontab

A crontab file defines the cron jobs of a user or system. You can edit it by running crontab -e.

Each line of a crontab represents a job. This is the schema:

# ┌───────────── minute (0 - 59)
# │ ┌───────────── hour (0 - 23)
# │ │ ┌───────────── day of the month (1 - 31)
# │ │ │ ┌───────────── month (1 - 12)
# │ │ │ │ ┌───────────── day of the week (0 - 6) (Sunday to Saturday)
# │ │ │ │ │
# * * * * * <command to execute>

If a * is at one position, it is unrestricted. If minute is *, it will run every minute (but not necessarily every hour or day).

You can also specify */n to run every n-th interval. Setting hour to */5 it will run every five hours.