First of all let me apologize for the vague question title.
Here is a better explanation ...
I have an Ubuntu PC which I am using as a web server. It will normally run headless. When it is powered up it needs to boot automatically without any body entering a user name or password, so I guess we call this autologin.
If someone were to plug in a keyboard, mouse and monitor then they would have access to the system and the .php web files which I need to protect.
How can I stop someone simply plugging in a keyboard etc and having unrestricted access. I'm happy to only be able to access the system via ssh using myusername, mypassword.