To secure your machine, there are hundred different things you can do, but the most important thing is to know what's happening on your Machine. In that getting the alerts as soon as someone login is one of very important and must thing to do.
So, to do the same thing, you can go with two approaches:
Fork Bomb, Pretty much clear by name, anything which uses the "fork" operation and explodes like a bomb is known as Fork Bomb. It's a form of DOS (Denial Of Service) attack, using fork operation, in which a running process can create another running process. Fork bomb is sometimes referred as wabbit. In other words, Fork Bomb is a particular species of wabbit that can be written in one line of code.
SSH is the most trusted protocol used in today's world for remote logins and secure file transfers from one machine to another. There are three different ways of authetication when trying to login with SSH protocol:
Q. How I should enforce users to change password at their first login ?
A. This is one of the very basic needs which shows up in most of the companies. As a system admin, I am sure this will be asked from you.
To setup this there are various ways, but I believe one of the very simplest one is the one I am going to explain below.
As soon as you connect to the internet to do any of your daily tasks or connect your server to provide some service, it means that you are exposing your system to lots of threat and to people who are ready to play with your system just for fun or some personal interest.