Linux, like any computer system, has a set of security issues that need to be considered. Regardless of what mechanisms are in place, the basic concepts are the same. In fact, the security of a computer system is very much like the security of your house, just as running a computer system is like running a household. You only want to let those people in that should be let in and you only want people accessing resources that they should. (Do you really want your 3-year-old playing with your collection of Dresden Porcellan?)
The term security is common enough. On a personal basis we think of it as freedom from risk or danger; being safe. We might also think of this as the methods we undertake to prevent someone from breaking into our house. In computer science terms, both of these ideas are applicable, depending on what you are referring to.
If we talk about being safe from risk when working with computers, we are often talking about things like regular backups and reliable hardware. Although these are very important issues, these are not what is generally meant when referring to security. On computers systems, security is more along the lines of preventing someone from breaking in. The definition can be expanded by saying computer security is preventing someone from doing something that they are not allowed to do. This could be anything from reading other peoples mail to stopping the printers.
In this section we’re are going to be talking about what mechanisms exist to keep people from poking around and doing things they shouldn’t. Well talk about what tools Linux provides to control access, change what users can access and how to make sure users are not even trying to do things they shouldn’t.