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Things you need to know about cron

cron is a Linux utility which schedules a command or script on your server to run automatically at a specified time and date. 
They're most commonly used for automating system maintenance or administration. However, they are also relevant to web application development. 

Why use cron? 

Server admins have been using cron jobs for a long time.  
  • You can expire and erase cached data files in a certain interval.
  • You can auto-check your website content for broken links and have a report e-mailed to yourself regularly.
  • Can update your database from external api 

Syntax

Here is a simple cron job:
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10 * * * * /usr/bin/php /www/virtual/username/cron.php > /dev/null 2>&1
It consists of five parts:
  1. minute
  2. hour
  3. day of month
  4. month
  5. day of week

Can generate the sequence from  crontab guru,   https://crontab.guru/every-30-minutes


Editing the Crontab

Running this command will launch vi (text editor) and will let you edit the contents of the crontab:
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crontab -e

If you would just like to see the existing crontab without editing it, you can run this command:
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crontab -l
To delete the contents of the crontab:
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crontab -r

For more details attached the reference link  below. 

Reference : 

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