Cron is the traditional service to schedule tasks (jobs) on Linux systems. Learn how to use cron using these simple steps (you can also use Systemd timers).

Table of Contents

Install cron if it’s not already installed

cronie is the package that contains the cron tool. You can install it using your package manager.

Starting and enabling the service

You need to start the cron service in order cron to work. Using systemd you can check if the service is active and running with this command:

systemctl status cron
  • Some systems use cronie or crond as the service name.

Start and enable the service with systemctl enable --now and the service name.

Scheduling cron jobs as root user

The root user uses the file /etc/crontab or, preferably, a cron table file inside /etc/cron.d/. You can also create hourly, daily, weekly and monthly jobs inside /etc/cron.hourly/, /etc/cron.daily/, etc.

An example cron table file inside /etc/cron.d/

Remember that # is used to create comments.

SHELL=/bin/bash
PATH=/sbin:/bin:/user/sbin:/usr/bin
MAILTO=root

# minute hour day_of_month month day_of_week username command

# Run a job every minute of every hour of every day
# * * * * * root some_command

# Run a job at 17:00 every Monday
# 0 17 * * mon root some_command

# Run a job every ten minutes
# 0/10 * * * * root some_command

Cron jobs inside cron.hourly, cron.daily, etc.

Files inside these folders are simple scripts:

#!/bin/bash

some_command

Schedule cron jobs as a non-root user

Non-root users can use the crontab utility to create cron jobs.

crontab -e

This command will prompt for a default editor. Then, it will show a file you can edit to add your cron jobs at the end.

# minute hour day_of_month month day_of_week command
# Run the script every day at 17:00
0 17 * * * /home/ricardo/script.sh

Anacron

anacron works like cron, but it does not assume that the machine is always running (some jobs in cron may never be started if the machine is off when job is scheduled). anacron may be already installed in some distros with cron (as part of cronie package) or you need to install it manually.

Anacron list jobs from the /etc/anacrontab file. This is a template of the content of this file:

SHELL=/bin/sh
PATH=/sbin:/bin:/usr/sbin:/usr/bin
MAILTO=root
# the maximal random delay added to the base delay of the jobs
RANDOM_DELAY=45
# the jobs will be started during the following hours only
START_HOURS_RANGE=3-22

#period in days   delay in minutes   job-identifier   command