Cron
cron is basically a job scheduler that can help automate many conventional but repeatedly used functionality.
Cron works using the crontab file.
It is a file that lists all the scheduled jobs and when to perform them.
On a standard Linux machine, there are different crontab files based on user privileges. We’ll mostly base our examples on the default users’ crontab.
crontab is the command that allows us to modify crontab files and cron executes them.
The jobs inside the crontab file are known as cron jobs, and consist of standard Linux commands. They also contain the time-period when cron needs to execute them.
┌───────────── minute (0 - 59) │ ┌───────────── hour (0 - 23) │ │ ┌───────────── day of the month (1 - 31) │ │ │ ┌───────────── month (1 - 12) │ │ │ │ ┌───────────── day of the week (0 - 6) (Sunday to Saturday; │ │ │ │ │ 7 is also Sunday on some systems) │ │ │ │ │ │ │ │ │ │ * * * * * <command to execute>
Deny Crontab Access to Specified Users
Limit Crontab Access to Specified Users
Send Cron Results to Specified Email Account
Useful Examples
Create a Backup of All User Accounts at 5 am Daily
Create a Backup of All User Accounts at 5 am Per Week
Schedule Cron to Execute a Job Twice a Day
Schedule Cron to Execute a Job at 2 am Daily
Schedule Cron to Execute a Job at 3:15 am Daily
Schedule Cron to Execute a Job at 8 pm Every Week
Schedule Cron to Execute a Job at 8 pm on Monday
Schedule a Cron Job at 8 pm on Monday, and Saturday
Schedule a Cron Job to Run on Every Minutes
Schedule a Cron Job to Run on Every 10 Minutes
Schedule a Cron Job to Run on Every 15 Minutes on Sunday and Monday
Schedule a Cron Job to Run on Specified Months
Schedule a Cron Job to Run on 15 January at 8 PM
Schedule a Cron Job to Run in Every Second Month
Schedule a Cron Job to Run on the First Sunday of Each Month
Schedule a Cron Job to Run on Every Three Hours
Schedule a Cron Job to Execute Twice on Every Saturday and Monday
Schedule a Cron Job to Run on Every 30 Seconds