Introduction to Cron, Crontab, and CronJobs for Beginners

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In the last blog we understood, what is Nmcli which is network manager command line tool to delete, create i.e. manage network connection which is easier way to handle the configuration.

1. What is Cron =

Cron is a command-line-utility tool which is used to schedule and automate repetitive task which has to done manually after specific interval.

Ex. If we want to take backup of the machine weekly, we will write a script and schedule it to run at specific interval

2. How Cron works =

Cron uses a deamon process (runs in the background) which is called as cron itself and it keeps eye on the date and time of the server on which it’s going to be executed to perform a specified task at the given time.

3. What is Cronjobs =

Its a job which is schedules by cron to perform the scheduled task automatically at given time.

4. What is crontab =

Its a command which is used to create a file, where user’s can mention the scheduled time and which task has to be performed i.e. a job which cron runs.

There are 3 commands

1. crontab -e = To create a file and edit it

2. crontab -l = To list the cronjobs

3. crontab -r = To remove the cronjobs

5. How the cronjob format is used =

A B C D E (command)

↓ ↓ ↓ ↓ ↓

↓ ↓ ↓ ↓ ↓

↓ ↓ ↓ ↓ day of the week(0 - 7) (Sun - 0)

↓ ↓ ↓ month (1 - 12)

↓ ↓ day of the month(1 - 31)

↓ hours(0 - 23)

↓

min(0 - 59)

Conclusion →

In this blog we understood, what is cron, cronjob and crontab. The requirement of cron is to reducing the manual intervention required to complete the repetitive task which is prone to human error. But cron solved this problem by automatically executing the task using cron demon background process.

Image credit → https://images.app.goo.gl/8jq5A5t8CWthc97m6