How to create a cron job in Linux

Cron Job is the job done by system cron every day or like timed, for a specific set of operations and processes like cleaning up, maintenance and more.

So If you have some process like cleaning up of logs every 7 days, or deleting files older than 7 days, or like clearing the cache. You can do with cron job.

let us see how can we do with an example of file deletion or directory deletion.

1. Open a terminal and enter the command below

crontab -e

it will open up the cron file for a user, where we can write the commands.

Note : For creating root user cron, do use sudo or sudo su before

2. If there are no cron jobs previously setup, a new file needs to be created. So you will be asked of the editor. Choose nano as the preferred option.

3. With nano editor opened. Do write the below code

# skip if the cron already have these
# this line ensures user is using the shell and bin while commands are executed
SHELL=/bin/sh
PATH=/etc:/bin:/sbin:/usr/bin:/usr/sbin
# Order of crontab fields for writing
# minute        hour    mday    month   wday    command
# TO remove a folder/directory somewhere
# TO run after each minute
* * * * * find /home/user/some-folder/* -type d -delete
# To run Daily
@daily find /home/user/some-folder/* -type d -delete
# TO remove a file/files somewhere
# TO run after each minute
* * * * * find /home/user/some-folder/* -type f -delete
# To run Daily
@daily find /home/user/some-folder/* -type f -delete

4. Ctrl + X to save or other combinations for your opened editor.

you will see the installed message, which means cron job is fine.

you can verify the cron job by setting the one minute time and see, then set back a different time.

5. You have successfully configured a crontab job. You can add your command in place of these to setup.

Note: commands are simple shell commands

Timing parameters can be set from below.

           string	   meaning
	   ------	   -------
	   @reboot	   Run once, at	startup	of cron.
	   @yearly	   Run once a year, "0 0 1 1 *".
	   @annually	   (same as @yearly)
	   @monthly	   Run once a month, "0	0 1 * *".
	   @weekly	   Run once a week, "0 0 * * 0".
	   @daily	   Run once a day, "0 0	* * *".
	   @midnight	   (same as @daily)
	   @hourly	   Run once an hour, "0	* * * *".
	   @every_minute   Run once a minute, "*/1 * * * *".
	   @every_second   Run once a second.

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