What is CronJob?

Cron is a program used to repeat a task at a later time. The act of issuing a command to repeat a specific task at a specific time is a cron job.
How does cron job work?
If you want to schedule a task once for a later time, you can use another command like it. But for repetitive tasks, cron is a great solution.
Cron is a daemon, meaning Cron runs in the background to execute non-interactive tasks. You must have heard of background processes such as Services in Windows.
A daemon is always in standby mode. So in this mode, it waits for command request from any other computer in the computer or network to do a specific task.
A cron file is a simple text file containing commands to run at a specific time. The default crontab file is /etc/crontab and is located in a crontab directory /etc/cron.*/. Only system administrators can edit the crontab file.
However, since Unix-like operating systems support multiple users, each of them can create their own crontab file and run commands to get tasks done whenever they want. A cron daemon will check the file and run the command in the system background.
With cron jobs, you can automate system maintenance, monitor disk space, and schedule backups. Because of their nature, cron jobs are great for a 24/7 computer, aka a server.
Remember that although cron jobs are mostly used by system administrators, they are also incredibly useful for web developers. For example, you can check for broken links to deactivate an expired account or even send newsletters to targeted users.

How to reach CronTab?

Crontab is a service used on Linux systems. Crontab allows a command, script or application to run at the time you specify or at certain time intervals.A cron schedule is a simple ASCII text file. Each user has their own cron calendar. This is usually located in /var/spool/cron/crontabs on Linux machines. Crontab files cannot be modified or created directly. You cannot access the file without using the “crontab” command.

Let’s test it out. This command stands for start our crontab.

After you press enter it shows you 3 options.

I pressed 1 because nano is way easy for beginners.

I want to create a file/folder, file name is howtocreatefile 5 stars with spaces stands for time. First star is minute(0–59), second star is hour(0–23),third star is day of the month(0–31),fourth star is month(0–12) and the last one is day of the week(0–7). Press control+x then in option that appear after that press y then press enter. This is saves and exits.

Let’s have a look our file with ls command.

It seems perfect! our file is there. As i said before if i put some numbers instead of the stars it is not create this quick. For example if i put 3 instead of first star our file are going to create after 3 minutes.

Let’s provide some other way for our file is created correctly.

As you see our file is created.

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