How to write cron jobs on AWS EC2 instance

Cron is a time-based job scheduler run on the server in the Unix-like operating system.
To perform such action we write cron expression made of five fields, followed by a shell command to execute.

1. First, we have to log in to AWS EC2 instance using CLI (Command Line Interface).
2. For log in, type:
   ssh -i <.pem file> username@ip_address
3. After successfully log in, type: 
   crontab -e
   then select any editor from the list (preferred nano).
4.  Type cron command. For example:
   * * * * * php /var/www/html/file/name.php
5. Now save the changes. If you are using nano editor type Ctrl + x and Select Y and then press Enter.
6. To list out all the running cron type:
   crontab -l

* is used for every minute, every hour, etc. Here ”php” is shell command followed by file location of php script, separated by white space.

If you want to run nodejs script then type:

Each from five stars represents a job:

Allowed special characters are:

Comma (,) – Commas are used to separate the item list.

For example:

• Cron to run at minute 1 and 10 every hour 
  1,10 * * * * php /var/www/html/file/name.php
• Cron to run at mid-night and mid-day 
  0 0,12 * * * php /var/www/html/file/name.php

Hyphen (-) – Hyphen defines range.

For example:

• Cron to run at every minute from 1 minute through 10 minute, every hour
  0-10 * * * * php /var/www/html/file/name.php
• Cron to run at minute 0 past every hour from 6 AM through 6 PM 
  0 6-18 * * * php /var/www/html/file/name.php

Slash (/) – Slash defines step values.

For example:

• Cron to run every 5th minute 
  */5 * * * * php /var/www/html/file/name.php
• Cron to run at minute 0 past every 6th hour 
  0 */6 * * * php /var/www/html/file/name.php

Sleep cron:

For example:

• Cron to run every minute after sleep of 30 seconds
  * * * * * sleep 30; php /var/www/html/file/name.php

Here are some examples:

• Once per minute 
  * * * * * php /var/www/html/file/name.php
  or 
  */1 * * * php /var/www/html/file/name.php
• Cron to run once per hour 
  0 * * * php /var/www/html/file/name.php
• Cron to run twice per hour 
  0,30 * * * php /var/www/html/file/name.php
• Cron to run once per day
  0 0 * * * php /var/www/html/file/name.php
• Cron to run on 1st and 15th of every month
  0 0 1,15 * * php /var/www/html/file/name.php