Preface

Approved by computer delinquents as an action manual.
Hackers

Approved by system administrators as a defense manual.
Admins

Overview

This book is devoted to exploring one of the most popular operating systems installed on servers: Linux. So far, this operating system has not been as popular among home users as among professional administrators. There have been, however, developments of late that make this system likely to capture a good segment of the home-computer operating system market. The operating system is becoming easier to install all the time, and its graphical user interface and the ease of use often give the most popular operating system among home users Windows a good run for its money.

This book will be of use to Linux administrators and to those Linux users who want to learn this operating system in more detail. The discussion of the configuration and security issues will come in handy for network security professionals, even those running other operating systems, because the larger part of the information is not tied to any specific operating system.

You will learn how hackers break into servers, and use the knowledge to prevent them from breaking into your server. Because some examples provided in the book can be used not only for defense but also for offense, I would like to give fair warning to young aspiring hackers. Curiosity is a commendable quality, but remember that the law is ever vigilant and always gets its man. If you get away with one break-in, next time you may not be so lucky and may have to spend some time in a company of unfortunate specimens of humankind, where your hacking skills will be of little use to you.

Some material in the book is presented from the hacker's point of view and describes methods of breaking into computer systems. I hope that this information will not actually be put to use. But being somewhat skeptical of the average human integrity, I tried to place more emphasis on defense against breaking in. I also left out some aspects and gave only a general description of others in order not to lead you into the temptation of applying these methods in practice.

You only need to spend a few minutes on programming or on Internet research to finalize my thoughts. Although this book can serve as a starting point for learning break-in techniques, I hope you will not use the acquired knowledge maliciously. If common morality is not enough to keep you from stepping onto the slippery path of computer burglary , remember the legal ramifications of your actions.

Any tool can be used for both useful and destructive purposes. A simple kitchen knife is a good example. It can be used as intended for its kitchen chores or as a defensive or killing weapon. Likewise, the hacker techniques discussed in this book can be used for everyday operating system maintenance as well as for defending against or perpetrating computer system break-ins. I hope that you will not use the acquired knowledge for destructive purposes, which will not add to your good name . As for cracker notoriety, why do you need it? You will be better off directing your efforts toward constructive pursuits.

Despite the obvious strivings by Linux to become an everyday home computer operating system, it is still quite difficult to configure and contains lots of options that most people simply do not need. "Security" is a misnomer when referring to a Linux system operated with its default configuration settings. But no operating system running at the default configuration settings can work reliably and be maximally secure. Software developers cannot possibly know each user's individual needs and strive to make the software work on any hardware configuration. To achieve this, they have to build many extraneous capabilities into their product.

It just happens that being a Linux administrator requires more knowledge and experience than being a Windows administrator. This is because Linux is more complex to configure. In this book, I try to explain this operating system in the most understandable terms; moreover, I try to do this from the hacker's point of view.

"What exactly is the hacker's point of view?" my readers often ask. To answer this question, you should have a clear idea of what a hacker is and what he or she sees in an operating system.

When I am asked how I understand what a hacker is, I answer with the following example: If you can install an operating system and get it working, then you are an administrator. But if you have tuned it up for maximum performance and security, than you are a hacker. Being a hacker means being able to create something better than others can, to make this something faster, more convenient , and more secure. This is what the Linux operating system is, which was created by hackers for the whole world to use.

This book considers the operating system starting from the basics and proceeding to the most complex manipulations with the system. The material is presented in language simple and comprehensible to everyone. This will make it possible for you to acquire essential Linux knowledge without having to use any supplementary literature, because you will learn all the necessary information from one source. For more detailed information, you can take advantage of the man, info , and help files supplied with the operating system.

This book is different from other books on the subject in that the security and performance are considered not in separate chapters at the end of the book doing this would be a big mistake but throughout the book as may be necessary. If a person acquires unproductive habits of working with the system, two chapters at the end of the book as an afterthought will not break these wrong habits to teach the right ones. This is why the performance and security of each area considered will be discussed immediately without putting it off until the end of the book.

You can always find instructions on how to simply use or even administer Linux on the Internet or in the software manuals. But information on how to use the operating system effectively is more difficult to come by and is usually gained in pieces from various sources, which makes it difficult to fuse this information into a solid body of knowledge. True security cannot be based on piecemeal information. Overlooking a single, seemingly trivial thing can leave your computer vulnerable to a break-in.

(For supplementary information on computer and network security, I recommend reading another of my books, Hackish PC , which provides a good deal of general information concerning computer and network protection.) Although this book deals mostly with the security of the Linux operating system, many of the questions considered can also be of use when building a secure Linux server. Windows security professionals can also derive benefits from the book's information.

The subject of viruses is not treated in the book, because currently the activity of Linux operating system viruses is minimal, which is not to say that there is no such threat. However small it may be, it always exists; but protecting against viruses is similar to protecting against Trojans, of which there are quite a few of the Linux variety. You can obtain more information about virus attacks and protection against them in the already-mentioned Hackish PC book of my authorship.

So, start discovering Linux. I am certain that you will see this operating system in an entirely different light and learn many new and interesting things.