In each server there are a lot of running processes which help the system work corectly. In some cases you can run your own script to achieve a certain functionality, if you run the script in background that means it will run all the time, after the server restart, the script will start with the system. 

To see a list with all these running processes you have to login via SSH you can use programs like Putty is very easy to use. After login with root you need to add the following command:

ps aux

Hit enter and you should see the following output:

To kill a process you only need the PID column, in the following article you I will show you how to kill a running process in linux CENTOS.