In the face of increased threats to computer systems, information security has grown to major importance in the world of computing. The menaces include external malicious attacks (from corporate espionage to hackers and crackers) and, if your system has users, internal security breaches (from disgruntled employees to unscrupulous visitors). Hardware, software, networks—the vulnerabilities are numerous. Unix security is as much philosophy as it is technical mastery. This chapter introduces the major security concepts and some commands you can use to make your systems more secure.

The Basics of Good Security

An age-old saying in computer security circles is that the only computer that is completely secure is one that is disconnected from any network, turned off, and embedded in a block of concrete. Of course, that's an exaggeration, but it does illustrate the point that no system is 100 percent secure. Security is not something that can be enabled by clicking one checkbox in the system, and it is not simply a matter of installing a software program and being done with it. Security is an ongoing journey, and one that can be fascinating.

Computer security is much like security in the real world. You probably have one or more locks on the front door of your house to discourage strangers from entering your home and helping themselves to your belongings. While you have made an effort to safeguard your home, you probably can imagine a situation in which your security measures ...

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