Disable a Service during Start-up

To disable any service from starting automatically during boot-up, do the following:
# Say for example you want to disable mysql from auto-start, open the terminal and enter the following:
echo manual | sudo tee /etc/init/mysql.override

This will create a file called mysql.override and dump the content "manual" in it. This will be override mysql program to start automatically while boot-up. To enable auto-start, either remove the file or the content "manual".