Linux Essentials

Christine Bresnahan, Richard Blum

• Éditeur: Sybex
• Année: 2015
• ISBN:
  9781119092148
• Édition: 2
• Sujet: Informatique
• Sous-sujet: Systèmes d'exploitation

Learn Linux, and take your career to the next level!

Linux Essentials, 2 nd Edition provides a solid foundation of knowledge for anyone considering a career in information technology, for anyone new to the Linux operating system, and for anyone who is preparing to sit for the Linux Essentials Exam. Through this engaging resource, you can access key information in a learning-by-doing style. Hands-on tutorials and end-of-chapter exercises and review questions lead you in both learning and applying new information—information that will help you achieve your goals! With the experience provided in this compelling reference, you can sit down for the Linux Essentials Exam with confidence.

An open source operating system, Linux is a UNIX-based platform that is freely updated by developers. The nature of its development means that Linux is a low-cost and secure alternative to other operating systems, and is used in many different IT environments. Passing the Linux Essentials Exam prepares you to apply your knowledge regarding this operating system within the workforce.

• Access lessons that are organized by task, allowing you to quickly identify the topics you are looking for and navigate the comprehensive information presented by the book
• Discover the basics of the Linux operating system, including distributions, types of open source applications, freeware, licensing, operations, navigation, and more
• Explore command functions, including navigating the command line, turning commands into scripts, and more
• Identify and create user types, users, and groups

Linux Essentials, 2 nd Edition is a critical resource for anyone starting a career in IT or anyone new to the Linux operating system.

CHAPTER 1
Selecting an Operating System

The fact that you’re reading this book means you want to learn about the Linux operating system (OS). To begin this journey, you must first understand what an OS is and what type of OS Linux is. This chapter is therefore devoted to these basic issues.

In this chapter, we describe what an OS is, how users interact with an OS, how Linux compares with other OSs with which you may be familiar, and how specific Linux implementations vary. Understanding these issues will help you find your way as you learn about Linux and switch between Linux-based and other systems.

• What is an OS?
• Investigating user interfaces
• Where does Linux fit in the OS world?
• What is a distribution?

What Is an OS?

An operating system, or OS, provides all of the most fundamental features of a computer, at least from a software point of view. An OS enables you to use the computer’s hardware devices, defines the user interface standards, and provides the basic tools that begin to make the computer useful. Ultimately, many of these features trace their way back to the OS’s kernel, which is described in more detail next. Other OS features are owed to additional programs that run atop the kernel, as described later in this chapter.

What Is a Kernel?

An OS kernel is a software component that’s responsible for managing various low-level features of the computer, including the following:

• Interfacing with hardware devices (network adapters, hard drives, and so on)
• Allocating memory to individual programs
• Allocating CPU time to individual programs
• Enabling programs to interact with each other

When you use a program (say, a web browser), it relies on the kernel for many of its basic functions. The web browser can communicate with the outside world only by using network functions provided by the kernel. The kernel allocates memory and CPU time to the web browser, without which it couldn’t run. The web browser may rely on plug-ins to display multimedia content; such programs are launched by and interact with the web browser through kernel services. Similar comments apply to any program that you run on a computer, although the details vary from one OS to another and from one program to another.

In sum, the kernel is the software “glue” that holds the computer together. Without a kernel, a modern computer can do very little.

Kernels are not interchangeable; the Linux kernel is different from the Mac OS X kernel or the Windows kernel. Each of these kernels uses a different internal design and provides different software interfaces for programs to use. Thus, each OS is built from the kernel up and uses its own set of programs that further define each OS’s features.

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Many programs run on multiple kernels, but most need OS-specific tweaks. Programmers create binaries—the program files for a particular processor and kernel—for each OS.

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Linux uses a kernel called Linux—in fact, technically speaking, the word Linux refers only to the kernel. Nonkernel programs provide other features that you might associate with Linux, most of which are available on other platforms, as described next in “What Else Identifies an OS.”

A student named Linus Torvalds created the Linux kernel in 1991. Linux has evolved considerably since that time. Today it runs on a wide variety of CPUs and other hardware. The easiest way to learn about Linux is to use it on a desktop or laptop PC, so that’s the type of configuration that’s emphasized in this book. The Linux kernel, however, runs on everything from tiny cell phones to powerful supercomputers.

What Else Identifies an OS?

The kernel is at the core of any OS, but it’s a component that most users don’t directly manipulate. Instead, most users interact with a number of other software components, many of which are closely associated with particular OSs. Such programs include the following:

Command-Line Shells Years ago, users interacted with computers exclusively by typing commands in a program (known as a shell) that accepted such commands. The commands would rename files, launch programs, and so on. Although many computer users today don’t use text-mode shells, they’re still important for intermediate and advanced Linux users, so we describe them in more detail in Chapter 6, “Getting to Know the Command Line,” and subsequent chapters rely heavily on your ability to use a text-mode shell. Many shells are available, and which shells are available and popular vary from one OS to another. In Linux, a shell known as the Bourne Again Shell (bash or Bash) is popular.

Graphical User Interfaces A graphical user interface (GUI) is an improvement on a text-mode shell, at least from the perspective of a beginning user. Instead of typing in commands, GUIs rely on icons, menus, and a mouse pointer. The Windows and Mac OS both have their own OS-specific GUIs. Linux relies on a GUI known as the X Window System, or X for short. X is a basic GUI, so Linux also uses desktop environment program suites, such as GNOME or the K Desktop Environment (KDE), to provide a more complete user experience. It’s the differences among Linux desktop environments and the GUIs in Windows or OS X that will probably strike you most when you first begin using Linux.

Utility Programs Modern OSs invariably ship with a wide variety of simple utility programs—calculators, calendars, text editors, disk maintenance tools, and so on. These programs differ from one OS to another. Indeed, even the names and methods of launching...