IT training wiley ubuntu linux secrets apr 2009

By the time you have completed Ubuntu Linux Secrets you will be well-prepared to utilize your Ubuntu workstation or server to its fullest.. Ubuntu Linux Secrets also walks the seasoned

Ubuntu Linux

Secrets

Ubuntu Linux

Secrets

Richard Blum

10475 Crosspoint Boulevard

Indianapolis, IN 46256

www.wiley.com

Copyright © 2009 by Wiley Publishing, Inc., Indianapolis, Indiana

Published simultaneously in Canada

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—Proverbs 24:3–4 (NIV)

About the Author

Richard Blum has worked in the IT industry for over 20 years as both a systems and

network administrator During that time he has administered UNIX, Linux, Novell, and Microsoft servers, as well as helped manage desktop workstations on a 3,500-user net-work He has used Linux since the days of loading the system from floppy disks and has utilized Ubuntu workstations and servers in his environment

Rich has a bachelor of science degree in electrical engineering and a master of science degree in management, specializing in management information systems, from Purdue

University He is the author of several Linux books, including Linux Command Line and Shell Script Bible, Professional Assembly Language Programming, Network Performance Open Source Toolkit, sendmail for Linux, Running qmail, Postfix, and Open Source E‑mail Security He’s also a coauthor of Professional Linux Programming, and Linux for Dummies, 8th Edition When he’s not being a computer nerd, Rich plays bass guitar for his church

worship band and enjoys spending time with his wife, Barbara, and their two daughters, Katie Jane and Jessica

Finally, I would like to thank my parents, Mike and Joyce Blum, for their dedication and support while raising me, and my wife, Barbara and daughters, Katie Jane and Jessica, for their love, patience, and understanding, especially while I was writing this book.

Contents at a Glance

Introduction xxv

Part 1: Starting Out with Ubuntu 1

Chapter 1: What is Ubuntu? 3

Chapter 2: Playing with the LiveCD 25

Chapter 3: Installing Ubuntu 47

Chapter 4: Exploring the Desktop 79

Part 2: Starting Out with Ubuntu 107

Chapter 5: File Management 109

Chapter 6: Working With Text 135

Chapter 7: The OpenOffice Suite 161

Chapter 8: Network Applications 197

Chapter 9: Evolution 227

Chapter 10: Image Manipulation 255

Chapter 11: Using Audio 277

Chapter 12: Using Video 295

PART 3: Managing Your Workstation 313

Chapter 13: Software Installs and Updates 315

Chapter 14: Networking 337

Chapter 15: External Devices 367

Chapter 16: The Display 387

Chapter 17: Users and Groups 407

Chapter 18: Basic Administration 425

Chapter 19: The Ubuntu Command Line 441

PART 4: Using the Ubuntu Server 467

Chapter 20: DNS Server 469

Chapter 21: Web Server 493

Chapter 22: Samba and Print Server 521

Chapter 23: Email Server 547

Chapter 24: Database Server 579

Part 5: Programming in Ubuntu 605

Chapter 25: Shell Scripts 607

Chapter 26: Perl and Python 637

Chapter 27: C Programming 661

Chapter 28: Java 687

Chapter 29: Ruby 713

Chapter 30: PHP 741

Index 771

Introduction xxv

Part 1: Starting Out with Ubuntu 1

Chapter 1: What is Ubuntu? 3

What Is Linux? 4

The Linux Kernel 4

The GNU Utilities 11

The Linux Desktop Environment 13

Linux Distributions 19

Core Linux Distributions 19

Specialized Linux Distributions 20

The Linux LiveCD 21

What Is Ubuntu? 22

Ubuntu Versions 22

Ubuntu Release Schedule 23

Ubuntu Cousins 24

Summary 24

Chapter 2: Playing with the LiveCD 25

The Ubuntu LiveCD 26

Downloading Ubuntu 26

Downloading from the Web 27

Using BitTorrent to Download 29

Verifying the File 32

Creating the LiveCD 34

Burning CDs in Linux 34

Burning CDs in Mac OS X 34

Burning CDs in Windows 36

Booting the LiveCD 36

The Boot Process 37

Using Ubuntu 37

The LiveCD Desktop 39

Storing Files 40

Running Ubuntu in Windows 42

The Wubi Project 43

Installing in Windows 43

Running Ubuntu in Windows 44

Summary 45

Chapter 3: Installing Ubuntu 47

Preparing Your PC 48

System Requirements 48

Creating a Place for Ubuntu 51

Installing from the LiveCD 57

Select a Language 58

Select a Time Zone 58

Select a Keyboard 58

Prepare the Disk Space 60

Create a Login ID 63

Migrate Documents and Settings 64

Review Options 66

Installing from the Alternate Install CD 67

Guided Partitions 68

Manual Partitions 69

Server Installation 70

Main Installation 70

Server Programs 71

Upgrading Ubuntu 75

Summary 77

Chapter 4: Exploring the Desktop 79

Desktop Features 80

The Top Panel 81

The Desktop Workspace 86

The Bottom Panel 87

Modifying the Desktop 89

Adding to the Panel Menus 89

Adding Panel Applets 92

Adding Desktop Icons 96

Desktop Appearance 97

The Desktop Theme 98

The Background 99

Fonts 100

Interface 100

Visual Effects 101

Accessibility Features 101

Preferred Applications 102

Keyboard Features 104

Mouse Features 104

Summary 106

Part 2: Starting Out with Ubuntu 107

Chapter 5: File Management 109

The Linux Filesystem 110

Filepaths 110

Filenames 113

Nautilus 113

Nautilus Window Components 113

Browser Versus Spatial Mode 119

Modifying Nautilus Windows 120

Handling Files 125

Creating New Files and Folders 125

Copying and Moving Files 126

Running Programs 126

Deleting Files 128

File Properties 128

Basic Properties 128

Emblems 129

Permissions 130

Open With 132

Notes 133

Summary 133

Chapter 6: Working With Text 135

The gedit Editor 136

Starting gedit 136

Basic gedit Features 137

Setting Preferences 138

The Character Map 141

The vim Editor 143

The Basics of vim 143

Editing Data 145

Copy and Paste 146

Search and Substitute 146

The emacs Editor 147

Using emacs on the Console 148

Using emacs in GNOME 152

The Tomboy Notes Application 154

Starting Tomboy Notes 154

Creating Notes 155

Editing Notes 156

Organizing Notes 157

Changing Preferences 157

Tomboy Add-ins 159

Summary 159

Chapter 7: The OpenOffice Suite 161

The OpenOffice.org Suite 162

Word Processing 163

Writer Features 163

Working with Writer Files 167

Spreadsheets 168

The OpenOffice.org Calc Layout 168

Working with Calc Files 173

Presentations 174

Using the Presentation Wizard 174

Taking a Tour of OpenOffice.org Impress 176

Working with Impress Files 179

Database 180

Getting Help from the Wizard 180

Taking a Tour of Base 183

Working with Tables 184

Drawing 186

Taking a Tour of OpenOffice.org Draw 186

Working with Draw Files 189

Math 190

Starting Math 190

The Math Layout 191

Working with Math 193

Summary 195

Chapter 8: Network Applications 197

The Ubuntu Internet Software Suite 198

Ekiga 198

Firefox 200

Walking Through Firefox 201

Configuring Firefox 203

Working with Add-ons 210

Pidgin 212

Using the Pidgin Instant Messenger 213

Pidgin Preferences 215

Remote Desktop Viewer 216

Terminal Server Client 218

Transmission 220

gFTP 222

Summary 224

Chapter 9: Evolution 227

The Evolution Suite 228

Starting Evolution 228

Obtain Email Client Info 229

Run the Wizard 229

The Evolution Window 238

The Menu Bar 238

The Toolbar 239

The Search Tool 240

The Message List 240

The Sidebar 242

The Switcher 242

The Preview Pane 242

Using Evolution 242

Sending Messages 242

Changing the Configuration 244

Mail Filtering 247

Filtering Messages 247

Filtering Spam 249

Backing Up Evolution 250

Using the Address Book 250

Accessing the Calendar and Tasks 252

Calendar 252

Tasks 253

Summary 254

Chapter 10: Image Manipulation 255

Eye of GNOME Image Viewer 256

Using the Image Viewer 256

Supported File Types 260

The GIMP Image Editor 261

Starting GIMP 261

GIMP Basic Tools 261

Using GIMP 263

F-Spot Photo Manager 268

The F-Spot Layout 268

Using the F-Spot Editor 273

Summary 276

Chapter 11: Using Audio 277

Audio File Basics 278

Controlling Sound in Ubuntu 279

Sound Preferences 280

The Sound Applet 282

Rhythmbox 284

Playing Audio CDs 284

Playing Audio Files 286

Listening to Internet Audio 288

Ripping Audio CDs 289

Brasero 290

Sound Recorder 291

Playing Audio Files from Nautilus 292

Summary 294

Chapter 12: Using Video 295

Video Formats 296

The Totem Movie Player 297

The Totem Interface 298

The Totem Preferences Settings 301

Watching Web Clips 302

Checking Your Plug-ins 303

Adding Plug-ins 304

More Video Support 306

Editing Videos 307

Installing Kino 308

The Kino Interface 309

The Kino Preferences Settings 310

Summary 311

PART 3: Managing Your Workstation 313

Chapter 13: Software Installs and Updates 315

Software Management in Ubuntu 316

Software Packages 316

Software Repositories 316

Configuring Software Repositories 317

Installing Updates 319

The Update Manager 319

Using the Update Manager Applet 321

Installing New Applications 322

The Add/Remove Applications Window 322

Adding a New Application 324

Removing an Application 326

Installing New Packages 327

The Synaptic Layout 328

Installing Packages 331

Removing Packages 333

Command-Line Package Management 333

Setting Repositories 333

Apt-get Commands 334

Summary 336

Chapter 14: Networking 337

Networking Basics 338

Internet Connection Types 338

Ethernet Connections 341

Connecting to the Network 343

GNOME PPP 343

Network Manager 345

Network Tools 349

Devices 350

Ping 351

Netstat 352

Traceroute 354

Port Scan 355

Lookup 355

Finger 357

Whois 357

Firewalls 358

Installing Firestarter 359

Starting Firestarter 360

Using Firestarter 360

Summary 364

Chapter 15: External Devices 367

Printers 368

The Printer Configuration Tool 368

Printer Server Settings 369

Adding a New Printer 370

Modifying Printer Properties 372

Scanners 376

Detecting the Scanner 376

Scanning a Document 379

The Work Area 380

Digital Cameras 383

Portable Music Players 385

Summary 386

Chapter 16: The Display 387

The X Windows System 388

What Is X Windows? 388

Linux X Windows Software 389

The X.Org Configuration 390

Ubuntu Video Configuration 394

The Screen Resolution Utility 394

Setting Compiz Fusion Features 396

Monitor and Video Cards 401

Using 3-D Cards 403

Ubuntu 3-D Support 403

Viewing Restricted Hardware Drivers 404

Summary 404

Chapter 17: Users and Groups 407

The User Administration Tool 408

Adding Users 408

Modifying Users 412

Deleting Users 413

Ubuntu Groups 414

Adding Groups 416

Modifying Groups 417

Deleting Groups 418

User and Group Files 418

The Users File 418

The Groups File 419

Using the Command Line 420

Understanding File Permissions 421

File Properties 421

Changing File Permissions 422

Summary 423

Chapter 18: Basic Administration 425

Monitoring the System 426

System 426

Processes 427

Resources 429

File Systems 430

Log Files 431

Ubuntu Log Files 431

The System Log Viewer 432

Starting Services 433

Starting and Stopping Services 433

Service Properties 435

Sessions 436

Startup Programs 437

Options 437

Disk Usage Analyzer 438

Summary 440

Chapter 19: The Ubuntu Command Line 441

The GNOME Terminal Program 442

Session Tabs 442

The Menu Bar 443

The Command-Line Parameters 446

Command-Line Basics 447

Setting the Command Prompt 447

The bash Manual 449

Traversing Directories 451

File and Directory Listing 452

File Handling 458

Directory Handling 464

Summary 466

PART 4: Using the Ubuntu Server 467

Chapter 20: DNS Server 469

History of Computer Names 470

Domain Names 470

DNS Structure 470

Finding Domains 472

DNS Database Records 473

DNS Protocol 478

Ubuntu as a DNS Client 478

Configuring DNS Client Files 479

Ubuntu Client DNS Programs 480

Ubuntu as a DNS Server 486

The named Files 486

Using named as a Local Cache Server 488

Using named as a Master DNS Server 489

Summary 492

Chapter 21: Web Server 493

Ubuntu Web Servers 494

Web Scripting Languages 494

The LAMP Platform 498

The Tomcat Platform 498

The Apache Web Server 499

Apache Configuration Files 500

Apache Modules 500

Creating Virtual Hosts 502

Testing the Apache Server 503

The MySQL Software 506

Accessing the Server 506

Changing the Root Password 507

The phpMyAdmin Tool 508

The PHP Software 510

The PHP Configuration Files 510

PHP Extensions 511

Using PHP 513

Tomcat 514

Tomcat Configuration 515

Testing Tomcat 515

Managing Tomcat 518

Summary 520

Chapter 22: Samba and Print Server 521

What Is Samba? 522

The Ubuntu Samba Environment 523

Samba Programs 523

Samba Configuration Files 524

Creating a Samba Server 531

Editing the smb.conf File 531

Defining Samba Passwords 532

Managing Samba 533

The Samba Client 533

The smbclient Program 533

Interacting with a Windows Share 534

Connecting from Windows 537

The CUPS Print Server 539

Printing in Linux 539The CUPS Software 541CUPS Configuration 541Managing CUPS Printers 542Summary 546

Chapter 23: Email Server 547

How Email Works 548

Mail Transfer Agent 549Mail Delivery Agent 551Mail User Agent 553Postfix Setup 557

Postfix Core Programs 558Postfix Message Queues 559Postfix Utility Programs 560Postfix Configuration Files 561Postfix Lookup Tables 562Installing Postfix 563

Internet Site 563Internet with SmartHost 564Satellite System 565Local Only 566Configuring Postfix 567

Wizard Windows 566Modifying Configuration Settings 573procmail 574

The procmailrc File 574Using procmail 576Summary 578

Chapter 24: Database Server 579

The MySQL Server 580

The MySQL Server Files 580The mysql Command 585Using mysql 588The PostgreSQL Server 590

The PostgreSQL Files 591The psql Command 594Using psql 597Working with Databases 599

Creating a Database 599Managing Users 600Building Tables 602Adding and Viewing Data 603Summary 604

Part 5: Programming in Ubuntu 605

Chapter 25: Shell Scripts 607

Using Multiple Commands 608

Creating a Script File 608

Displaying Output 610

Using Variables 612

Environment Variables 612User Variables 613The Backtick 615

Redirecting Input and Output 616

Output Redirection 616Input Redirection 617Pipes 618

Performing Math 620

The expr Command 620Using Brackets 622

A Floating-Point Solution 623Exiting the Script 626

Checking the Exit Status 627The exit Command 628Structured Commands 629

The if-then-else Statement 629The test Command 631Summary 636

Chapter 26: Perl and Python 637

What Is Perl? 638

Working with Perl 638

Command-Line Interpreter 639Creating a Perl Program 640Perl Programming 640

Using Variables in Perl 641Structured Commands 644Perl Operators 646Regular Expressions 648Perl Command-Line Arguments 650Perl Modules and CPAN 651

Summary 659

Chapter 27: C Programming 661

C Programming in Ubuntu 662

The GNU Compiler 662The GNU Assembler 665The GNU Linker 668The GNU Debugger Program 671The GNU objdump Program 674The GNU Profiler Program 676Writing C Programs 681

C Program Format 681Sample Program 684Summary 685

Chapter 28: Java 687

The Java Development Environment 688

Java Programs 688Platforms 689Ubuntu Java Environments 690

Using OpenJDK 691

Installing OpenJDK 692OpenJDK Components 692Java Development Environments 693

Command-Line Tools 694NetBeans 703Eclipse 707Summary 711

Chapter 29: Ruby 713

What Is Ruby? 714

Ruby on the Web 714Ruby on Rails 715Installing Ruby 715

Ruby Components 715Installing Ruby in Ubuntu 716Working with Ruby Code 719

Interactive Ruby 719Scripting with Ruby 720Embedded Ruby 721The Ruby Language 722

Variables 722Structured Commands 725Object-Oriented Programming 730

Creating Classes 730Using Objects 731Adding Methods 732

Ruby on Rails 732

Creating a Project 733Testing the Project 736Summary 739

Chapter 30: PHP 741

What Is PHP? 742

PHP in Ubuntu 743

Core Installation 743PHP Extensions 745Working with PHP 747

Defining PHP Code 747PHP Output 749The PHP Language 751

PHP Variables 751Iterating Through Arrays 754Structured Commands 754Including External Files 756Working with MySQL 759Object-Oriented PHP 760

Creating a Class in PHP 761Creating Objects 761Writing OOP Code in PHP 762Expanding on OOP 763Class Constructors 765PECL and PEAR 768

Summary 768

Index 771

Welcome to Ubuntu Linux Secrets Like all books in the Secrets series, you can expect to

find both hands-on tutorials and real-world practical application information, as well as reference and background information that provides a context for what you are learning

This book is a fairly comprehensive resource on the Ubuntu Linux distribution By the

time you have completed Ubuntu Linux Secrets you will be well-prepared to utilize your

Ubuntu workstation or server to its fullest

Who Should Read This Book

If you’re new to the Linux world, you’ll benefit greatly from this book’s hands-on approach

The book walks through all of the steps required for setting up an Ubuntu Linux system, guiding you through the pitfalls and offering practical advice for getting your Ubuntu workstation up and running It then walks through all of the applications you’ll find on your new system, showing you how to use the office productivity software; work with images, audio and video clips on your desktop; run CDs and DVDs; and interact with the Internet

If you’re an advanced Linux enthusiast, you’ll also benefit from Ubuntu Linux Secrets

Nowadays it’s easy to get lost in the graphical world of prebuilt desktop packages Most desktop Linux distributions try their best to hide the Linux system from the typical user

However, there are times when you have to know what’s going on under the hood This book shows you how to use the Ubuntu administration features to manage your system, including monitoring programs, users, and disk space It shows how to access the Linux command-line prompt and what to do once you get there It also explains how to use your Ubuntu system as a complete program development platform, discussing how to program using shell, Perl, and Python scripts; the C, Java, and Ruby programming languages; and the PHP web-scripting language

Ubuntu Linux Secrets also walks the seasoned system administrator through how to use

the various server software packages included in the Ubuntu server distribution It cusses how to set up a complete web server using both the LAMP and Tomcat web servers and a database server using the popular MySQL or the feature-rich PostgreSQL database package, how to interact on a Microsoft Windows network using the Samba software, and how to create an email server for your home or organization

dis-How This Book Is Organized

This book is organized to lead you through the basics of the Ubuntu Linux distribution features, from installing your system to using the installed applications The book is divided into five parts, each one building on the previous parts

Part 1 starts you out on your Ubuntu Linux journey by helping you get your Ubuntu system running Chapter 1, “What Is Ubuntu?” walks through the complicated world of Linux distributions, describing why there are so many distributions and what the Ubuntu

Linux distribution has to offer After explaining the basics of the Ubuntu system, Part 1 continues with

Downloading and working with the Ubuntu LiveCD (Chapter 2)

♦

♦Installing Ubuntu on your PC (Chapter 3)

♦

♦Exploring the features of the GNOME desktop (Chapter 4)

♦

♦

In Part 2, the book takes you through the features you’ll find in the Ubuntu workstation:

Working with files and folders in Ubuntu (Chapter 5)

♦

♦Working with text files using the Ubuntu text editors (Chapter 6)

♦

♦Using the OpenOffice.org office productivity suite (Chapter 7)

♦

♦Becoming familiar with the Ubuntu Network applications (Chapter 8)

♦

♦Accessing your email with the Evolution email software (Chapter 9)

♦

♦Working with image files (Chapter 10)

♦

♦Playing and ripping CDs (Chapter 11)

♦

♦Playing DVDs and watching video clips from the Internet (Chapter 12)

♦

♦Part 3 shows you how to manage your Ubuntu system:

Installing and updating software packages (Chapter 13)

♦

♦Configuring network access (Chapter 14)

♦

♦Installing and using external devices such as printers and scanners (Chapter 15)

♦

♦Configuring your display and setting up multiple monitors (Chapter 16)

♦

♦Adding new users (Chapter 17)

♦

♦Controlling running programs and monitoring the system (Chapter 18)

♦

♦Using the Ubuntu command line (Chapter 19)

♦

♦

In Part 4, you’ll see how to install and configure the Ubuntu server packages:

Creating a domain name server (DNS) (Chapter 20)

♦

♦Maintaining a web server for dynamic web applications (Chapter 21)

♦

♦Using Samba to interact with other devices on a Microsoft Windows network

♦

♦(Chapter 22)Managing a complete email server (Chapter 23)

♦

♦Running a full-featured database server using either MySQL or PostgreSQL

♦

♦(Chapter 24)The last section of the book, Part 5, demonstrates how to use your Ubuntu workstation as

a complete programming development environment:

Writing and running shell scripts from the Ubuntu command line (Chapter 25)

♦

♦Working with Perl and Python scripts to manipulate data (Chapter 26)

♦

♦Using the C programming language to create professional applications

♦

♦(Chapter 27)Installing the Java programming environment to write applications (Chapter 28)

♦

♦Installing Ruby to write local and web applications (Chapter 29)

♦

♦Using PHP on the Ubuntu LAMP server to write dynamic web applications

♦

♦(Chapter 30)

Conventions and Features

There are many different organizational and typographical features throughout this book designed to help you get the most of the information

Secrets

When the author wants to provide additional information to help you get the most out of your Ubuntu system, the information will appear in a Secrets sidebar, separate from the main chapter material

Minimum Requirements

To get the most from the Ubuntu workstation software you must have a PC with at least a 700-MHz processor, 384 MB of system memory (RAM), 8 GB of disk space, and a graph-ics card capable of at least 1024 × 768 resolution It also helps to have a sound card if you plan on working with audio and video, and a network card if you plan on interacting with

a local network or the Internet

Where to Go from Here

Once you’ve completed Ubuntu Linux Secrets you’ll be well on your way to being an

Ubuntu Linux guru In the ever-changing world of Linux, it’s always a good idea to stay

in touch with new developments The Ubuntu Linux distribution comes out with a new version every 6 months, adding new features and removing some older ones To keep your knowledge of Ubuntu fresh, it’s important to stay well informed Find a good Linux forum on the web and monitor what’s going on in the Linux world There are many popular sites, such as Slashdot and Distrowatch, that provide up-to-the-minute information about advances in Linux It’s also a good idea to keep an eye on the Ubuntu distribution site itself Each new release goes through a series of beta releases, which are a great way to

be introduced to new features before they’re released in the next version

The information in the Secrets sidebars is important and is set off in a separate paragraph with a special icon Secrets provide additional information about things

to watch out for, tips on how to better use a feature, or background information that helps in understanding a topic

Starting Out with Ubuntu

Chapter 1: What Is Ubuntu?

Chapter 2: Playing with the LiveCD Chapter 3: Installing Ubuntu Chapter 4: Exploring the Desktop

What is Ubuntu?

Secrets in This Chapter

The Linux Kernel The GNU Utilities The Linux Desktop Environments Linux Distributions

Ubuntu Linux

1

One of the most confusing features of Linux is the concept of a distribution Many

novice Linux users get confused about what a distribution is and why there are so many of them

Before diving into the world of Ubuntu, it often helps to have an understanding of what Linux is and how it relates to Ubuntu This will help you understand where Ubuntu came from, and you’ll have a better idea of which flavor of Ubuntu is right for you With that in mind, this chapter explains what Linux and Linux distributions are, then it explains the pieces that specifically make up the Ubuntu Linux distribution It finishes by walking through different Ubuntu distributions and discussing what each provides

What Is Linux?

If Ubuntu is your first experience with Linux, you may be confused about why there are so many different versions of it I’m sure you have heard various terms such as “distribution,”

“LiveCD,” and “GNU” when looking at Linux packages—and have been confused

Trying to wade through the world of Linux for the first time can be a tricky experience

Even for experienced Linux users, trying to figure out the features that distinguish ferent distributions can be tricky This section walks through exactly what Linux is and describes each of its components

dif-For starters, there are four main parts of a Linux system:

The Linux kernel

♦

♦The GNU utilities

♦

♦Windows management software

♦

♦Application software

♦

♦Each of these four parts has a specific job in the Linux system However, each of the parts

by itself isn’t very useful You need all of them in one package to have a Linux system

Figure 1-1 shows a basic diagram of how the parts fit together to create the overall Linux system

This section describes these four main parts in detail and gives you an overview of how they work together to create a complete Linux system

The Linux Kernel

The core of the Linux system is the kernel The kernel controls all of the hardware and ware on the computer system, allocating hardware when necessary, and executing software when required

soft-If you’ve been following the Linux world at all, no doubt you’ve heard the name Linus Torvalds Linus is the person responsible for creating the first Linux kernel software, when

he was a student at the University of Helsinki He intended it to be a copy of the UNIX system, at the time a popular operating system used at many universities

After developing the Linux kernel, Linus released it to the Internet community and ited suggestions for improving it This simple process started a revolution in the world of computer operating systems Soon Linus was receiving suggestions from students as well

solic-as professional programmers from around the world

Application Software

WindowsManagement

SystemUtilities

Linux kernel

computer hardware

Figure 1-1: The Linux system

Allowing anyone to change programming code in the kernel would result in complete chaos Therefore, to simplify things, Linus acted as a central point for all improvement suggestions It was ultimately Linus’s decision whether or not to incorporate suggested code in the kernel This same concept is still in place with the Linux kernel code, except instead of Linus controlling the kernel code alone, a team of developers has taken on the task

The kernel is primarily responsible for four main functions:

System memory management

♦

♦Software program management

♦

♦Hardware management

♦

♦Filesystem management

♦

♦The following sections explore each of these functions in more detail

System Memory Management

One of the primary functions of the operating system kernel is memory management

Not only does the kernel manage the physical memory available on the server, it can also

create and manage virtual memory, or memory that does not actually exist.

It does this by using space on the hard disk, called the swap space The kernel swaps the

contents of virtual memory locations back and forth from the swap space to the actual physical memory This process allows the system to think there is more memory available than what physically exists (as shown in Figure 1-2)

Virtual Memory

PhysicalMemory

Swap Space

The Kernel

Figure 1-2: The Linux system memory usage

The memory locations are grouped into blocks called pages The kernel locates each page

of memory in either the physical memory or the swap space It then maintains a table of the memory pages that indicates which pages are in physical memory and which pages are swapped out to disk

The kernel keeps track of which memory pages are in use and automatically copies memory pages that have not been accessed for a period of time to the swap space area

(called swapping out) When a program wants to access a memory page that has been

swapped out, the kernel must make room for it in physical memory by swapping out a different memory page and swap in the required page from the swap space Obviously, this process takes time, and it can slow down a running process The process of swapping out memory pages for running applications continues for as long as the Linux system is running

You can see the current status of the memory on a Ubuntu system by using the System Monitor utility, as shown in Figure 1-3

The Memory graph shows that this Linux system has 380.5 MB of physical memory It also shows that about 148.3 MB is currently being used The next line shows that there is about 235.3 MB of swap space memory available on this system, with none in use at the time

By default, each process running on the Linux system has its own private memory pages

One process cannot access memory pages being used by another process

The kernel maintains its own memory areas For security purposes, no processes can access memory used by the kernel processes Each individual user on the system also has

a private memory area used for handling any applications the user starts

Often, however, related applications run that must communicate with each other One

way to do this is through data sharing To facilitate data sharing, you can create shared memory pages.

Figure 1-3: The Ubuntu System Monitor utility, showing the current memory usage.

A shared memory page allows multiple processes to read and write to the same shared memory area The kernel maintains and administers the shared memory areas, control-ling which processes are allowed access to the shared area

The special ipcs command allows us to view the current shared memory pages on the system Here’s the output from a sample ipcs command:

test@testbox:~$ ipcs -m - Shared Memory Segments -key shmid owner perms bytes nattch status0x00000000 557056 test 600 393216 2 dest0x00000000 589825 test 600 393216 2 dest0x00000000 622594 test 600 393216 2 dest0x00000000 655363 test 600 393216 2 dest0x00000000 688132 test 600 393216 2 dest0x00000000 720901 test 600 196608 2 dest0x00000000 753670 test 600 393216 2 dest0x00000000 1212423 test 600 393216 2 dest0x00000000 819208 test 600 196608 2 dest0x00000000 851977 test 600 393216 2 dest0x00000000 1179658 test 600 393216 2 dest0x00000000 1245195 test 600 196608 2 dest0x00000000 1277964 test 600 16384 2 dest0x00000000 1441805 test 600 393216 2 desttest@testbox:~$

Each shared memory segment has an owner that created the segment Each segment also has a standard Linux permissions setting that sets the availability of the segment for other users The key value is used to allow other users to gain access to the shared memory segment.

Software Program Management

The Linux operating system calls a running program a process A process can run in the

foreground, displaying output on a display, or it can run in the background, behind the scenes The kernel controls how the Linux system manages all the processes running on the system

The kernel creates the first process, called the init process, to start all other processes on

the system When the kernel starts, it loads the init process into virtual memory As the kernel starts each additional process, it allocates to it a unique area in virtual memory to store the data and code that the process uses

Most Linux implementations contain a table (or tables) of processes that start cally on boot-up This table is often located in the special file /etc/inittabs However, the Ubuntu Linux system uses a slightly different format, storing multiple table files in the /etc/event.d folder by default

automati-The Linux operating system uses an init system that utilizes run levels A run level can

be used to direct the init process to run only certain types of processes, as defined in the /etc/inittabs file or the files in the /etc/event.d folder There are seven init run levels in the Linux operating system Level 0 is for when the system is halted, and level

6 is for when the system is rebooting Levels 1 through 5 manage the Linux system while it’s operating

At run level 1, only the basic system processes are started, along with one console

ter-minal process This is called Single User mode Single User mode is most often used for

emergency filesystem maintenance when something is broken Obviously, in this mode only one person (usually the administrator) can log into the system to manipulate data

The standard init run level is 3 At this run level most application software, such as work support software, is started Another popular run level in Linux is 5 This is the run level where the system starts the graphical X Window software and allows you to log in using a graphical desktop window

net-The Linux system can control the overall system functionality by controlling the init run level By changing the run level from 3 to 5, the system can change from a console-based system to an advanced, graphical X Window system

Later on, in Chapter 19, “The Command Line,” you’ll see how to use the ps command to view the processes currently running on the Ubuntu system Here are a few lines extracted from the output of the ps command:

test@testbox~$ ps axPID TTY STAT TIME COMMAND

All other processes that start after the init process are assigned PIDs in numerical order

No two processes can have the same PID

The third column shows the current status of the process The first letter represents the state the process is in (S for sleeping, R for running) The process name is shown in the last column Processes that are in brackets have been swapped out of memory to the disk swap space due to inactivity You can see that some of the processes have been swapped out, but the running processes have not

Hardware Management

Still another responsibility for the kernel is hardware management Any device that the Linux system must communicate with needs driver code inside the kernel code The driver code allows the kernel to pass data back and forth to the device, acting as a intermedi-ary between applications and the hardware Two methods are used for inserting device driver code in the Linux kernel:

Drivers compiled in the kernel

♦

♦Driver modules added to the kernel

♦

♦Previously, the only way to insert a device driver code was to recompile the kernel

Each time you added a new device to the system, you had to recompile the kernel code

This process became even more inefficient as Linux kernels supported more hardware

Fortunately, Linux developers devised a better method to insert driver code into the ning kernel

run-Programmers developed the concept of kernel modules to allow you to insert driver code

into a running kernel without having to recompile the kernel Also, a kernel module can

be removed from the kernel when the device is finished being used This improvement greatly simplified and expanded the use of hardware with Linux

The Linux system identifies hardware devices as special files, called device files There

are three classifications of device files:

Character

♦

♦Block

♦

♦Network

♦

♦

Character device files are for devices that can handle data only one character at a time

Most types of modems and terminals are created as character files Block files are for

devices that can handle data in large blocks at a time, such as disk drives

The network file types are used for devices that use packets to send and receive data These

devices include network cards and a special loopback mechanism that allows the Linux system to communicate with itself using common network programming protocols

Linux creates special files, called nodes, for each device on the system All communication

with the device is performed through the device node Each node has a unique number pair that identifies it to the Linux kernel The number pair includes a major and a minor device number Similar devices are grouped into the same major device number The minor device number is used to identify a specific device within the major device group

This is an example of device files on a Linux server:

test@testbox~$ ls -al sda*

brw-rw 1 root disk 8, 0 2008-05-07 11:42 /dev/sdabrw-rw 1 root disk 8, 1 2008-05-07 11:42 /dev/sda1brw-rw 1 root disk 8, 2 2008-05-07 11:42 /dev/sda2brw-rw 1 root disk 8, 5 2008-05-07 11:42 /dev/sda5test@testbox~$ ls -al ttyS*

crw-rw 1 root dialout 4, 64 2008-05-07 11:42 /dev/ttyS0crw-rw 1 root dialout 4, 65 2008-05-07 11:42 /dev/ttyS1crw-rw 1 root dialout 4, 66 2008-05-07 11:42 /dev/ttyS2crw-rw 1 root dialout 4, 67 2008-05-07 11:42 /dev/ttyS3test@testbox~$

The sda device is the first SCSI hard drive, and the ttyS devices are the standard IBM-PC COM ports The list shows all of the sda devices that were created on the sample Ubuntu system Similarly, the list shows all of the ttyS devices created

The fifth column is the major device node number Notice that all of the sda devices have the same major device node, 8, while all of the ttyS devices use 4 The sixth column is the minor device node number Each device within a major number has a unique minor device node number

The first column indicates the permissions for the device file The first character of the missions indicates the type of file Notice that the SCSI hard drive files are all marked as block (b) device, while the COM port device files are marked as character (c) devices

per-Filesystem Management

Unlike some other operating systems, the Linux kernel can support different types of systems to read and write data to hard drives Besides having over a dozen filesystems of its own, Linux can read and write to filesystems used by other operating systems, such as Microsoft Windows The kernel must be compiled with support for all types of filesystems that the system will use Table 1-1 lists the standard filesystems that a Linux system can use to read and write data