The Official Ubuntu Server Book
Admin 101, Security
Book publishers are struggling along with the rest of the economy right now. The Web has a lot to do with declining sales, seeing that most of what you would find in a book can be had through a few Google searches. Finding information you can't get anywhere else is really the only reason left to buy a book in most people's mind.
After a brief introduction the author gets right down to business with chapter one covering installation. The discussion on special directories will be very helpful to anyone taking on Linux for the first time, especially someone coming over from the Windows world. There's also a good discussion of various server roles and which options you might want to select.
Chapter Two and Five will be where most owners of this book will use up their page marker stickies. If there's anything that intimidates a newbie system administrator, it has to be the command line. Once you get over the fear hump you'll find the logical arrangement of directories and use of configuration files pretty easy to understand. You'll also find yourself referring back to specific pages in the book to make sure you get the syntax of a particular command right.
Getting a good handle on the command line is what Chapter Two is all about. It presents the most common commands you'll need to perform basic administration tasks with and when you might need them. It also includes a concise discussion of the boot process and what a system administrator needs to know about it.
Chapter Five presents a number of specific roles a typical Linux server might perform and how you go about configuring each one. Linux servers have been used in these roles for years, and the steps to configure a server for a specific task are not difficult. In some instances it can be a little tedious, and having a good explanation of the different steps will make it easier to understand.
Every server administrator needs to know the concepts behind Linux security and how to configure the stock Linux security tools. Chapter Six lays out a list of things you need to understand when administering a Linux server and what you need to do to secure things like the sudo command so that someone doesn't inadvertently or maliciously take your server down. It also includes a discussion of some of the more common attacks you might see and how to deal with them.
File security has traditionally been handled on Linux and Unix systems with the basic permissions that are inherently a part of the operating system. This works great most of the time until someone gets access to a service or application running with root access. AppArmor is an open source project included with Ubuntu, providing access control to specific system services. Chapter Six includes the information you'll need to configure AppArmor for your server.
The biggest threat to any computer starts when you connect it to the outside world. While Linux servers are typically not vulnerable to the majority of the Windows attacks running around the Internet there are steps that need to be taken whenever you connect a machine to the network. There's a good discussion of firewalls and properly configuring SSH.