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Timothy Boronczyk and Christopher Negus Foreword by Karanbir Singh, Core Developer on the CentOS Project The book you need to succeed! Set up CentOS for your home or business Build enterprise-quality Linux ® servers Configure full-featured Linux desktop systems CentOS DVD Included! • Full version of CentOS 5.3

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  • Timothy Boronczyk and Christopher NegusForeword by Karanbir Singh, Core Developer on the CentOS Project

    BoronczykNegus

    The book you need to succeed!

    The first comprehensive guide to CentOSCentOS is a popular Linux distribution that is created from freely available enterprise-quality source code. Using CentOS can help you acquire the skills you need to become anything from a skilled Linux user to a professional Linux system administrator. With this thorough, step-by-step guide, you’ll not only learn how to install, configure, secure, and run CentOS, but also how to launch multimedia, add third-party software, use virtualization, set up networks, and more.

    • Install CentOS with anaconda and start configuration

    • Master Linux® shell commands and file systems

    • Learn your way around the GNOME® and KDE® desktop environments

    • Add or update software packages with RPM tools, yum, or PackageKit

    • Connect to the Internet and set up wired, wireless, and virtual networks

    • Configure print, file, mail, FTP, MySQL® database, Web, and other servers

    • Put CentOS to work as a router or firewall and protect your system

    Includes DVD with CentOS 5.3

    CentOS

    Shelving Category:COMPUTERS / Operating Systems / LinuxReader Level:Beginning to Advanced

    $54.99 USA $65.99 Canada

    Set up CentOS for your home or business

    Build enterprise-quality Linux® servers

    Configure full-featured Linux desktop systems

    www.wiley.com/compbooks

    CentOSDVD Included!• Full version of CentOS 5.3

    Reviewed for technical accuracy by a key member of the CentOS development team!

    What’s on the DVD?Find a full version of CentOS 5.3, install it today, and start using CentOS.

    System Requirements: See the DVD appendix for details and complete system requirements.

    Timothy Boronczykis a professional software developer by day, and a freelance programmer and author by night.

    Christopher Negusis the author of the bestselling Red Hat Linux Bible, Linux Toys, and Linux Toolbox series. He is an instructor for Red Hat, Inc., training students for RHCT and RHCE certification.

  • CentOS Bible

  • CentOS Bible

    Timothy BoronczykChristopher Negus

    Wiley Publishing, Inc.

  • CentOS Bible

    Published byWiley Publishing, Inc.10475 Crosspoint BoulevardIndianapolis, IN 46256www.wiley.com

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

    Published simultaneously in Canada

    ISBN: 978-0-470-48165-3

    Manufactured in the United States of America

    10 9 8 7 6 5 4 3 2 1

    No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form orby any means, electronic, mechanical, photocopying, recording, scanning or otherwise, except as permittedunder Sections 107 or 108 of the 1976 United States Copyright Act, without either the prior written per-mission of the Publisher, or authorization through payment of the appropriate per-copy fee to the Copy-right Clearance Center, 222 Rosewood Drive, Danvers, MA 01923, (978) 750-8400, fax (978) 646-8600.Requests to the Publisher for permission should be addressed to the Permissions Department, John Wiley& Sons, Inc., 111 River Street, Hoboken, NJ 07030, (201) 748-6011, fax (201) 748-6008, or online athttp://www.wiley.com/go/permissions.

    Limit of Liability/Disclaimer of Warranty: The publisher and the author make no representations orwarranties with respect to the accuracy or completeness of the contents of this work and specifically dis-claim all warranties, including without limitation warranties of fitness for a particular purpose. No war-ranty may be created or extended by sales or promotional materials. The advice and strategies containedherein may not be suitable for every situation. This work is sold with the understanding that the pub-lisher is not engaged in rendering legal, accounting, or other professional services. If professional assis-tance is required, the services of a competent professional person should be sought. Neither the publishernor the author shall be liable for damages arising herefrom. The fact that an organization or Web site isreferred to in this work as a citation and/or a potential source of further information does not mean thatthe author or the publisher endorses the information the organization or Web site may provide or recom-mendations it may make. Further, readers should be aware that Internet Web sites listed in this work mayhave changed or disappeared between when this work was written and when it is read.

    For general information on our other products and services please contact our Customer Care Departmentwithin the United States at (877) 762-2974, outside the United States at (317) 572-3993 or fax (317)572-4002.

    Wiley also publishes its books in a variety of electronic formats. Some content that appears in print maynot be available in electronic books.

    Library of Congress Control Number: 2009926357

    Trademarks: Wiley and the Wiley logo are trademarks or registered trademarks of John Wiley & Sons,Inc. and/or its affiliates, in the United States and other countries, and may not be used without writtenpermission. All other trademarks are the property of their respective owners. Wiley Publishing, Inc. is notassociated with any product or vendor mentioned in this book.

  • About the AuthorsTimothy Boronczyk is a native of Syracuse, NY, where he works as a software developer byday and a freelance developer, writer, and technical editor by night. He has been involved inweb design since 1998, with Linux since 2001, and over the years has written several articlesand tutorials. Timothy holds a degree in software application programming. In his spare time,he enjoys photography, hanging out with his friends, and sleeping with his feet hanging off theend of his bed. He’s easily distracted by shiny objects.

    Christopher Negus is the author of the best-selling Red Hat Linux Bible series, as well asthe author of Linux Toys, Linux Toolbox series, Linux Troubleshooting Bible, Linux Bible 2009edition, and dozens of other UNIX and Linux books. Chris is a Red Hat Certified Engineer(RHCE, cert #805008815534875), instructor (RHCI), and examiner (RHCX). Since 2008, Chrishas been employed by Red Hat, Inc. as an instructor, teaching RHCE-track courses. Earlier inhis career, Chris worked for eight years on development teams for the UNIX operating system atAT&T, where UNIX was created and developed.

    About the Technical EditorRalph Angenendt has been working as a system and network administrator since 1998. Afterbeing introduced to Linux in 1995, Ralph’s interest in non-UNIX-like operating systems hasdropped dramatically, so his work environment mostly consists of Linux servers.

    Besides having a sweet tooth for domesticating wild mail servers, Ralph also has a strong interestin automated system administration. Because of that he set up cfengine at his current employerto ease the pain of administrating a growing site.

    Since 2006, Ralph has been a member of the CentOS development team, where he leads thedocumentation force and does some infrastructure management. He might be met at a few OpenSource conventions in Europe, largely Germany and the Benelux countries.

  • Credits

    Acquisitions EditorJenny Watson

    Development EditorTom Dinse

    Technical EditorRalph Angenendt

    Production EditorDaniel Scribner

    Copy EditorCate Caffrey

    Editorial ManagerMary Beth Wakefield

    Production ManagerTim Tate

    Vice President and Executive GroupPublisherRichard Swadley

    Vice President and ExecutivePublisherBarry Pruett

    Associate PublisherJim Minatel

    Project Coordinator, CoverLynsey Stanford

    ProofreaderJen Larsen, Word One

    IndexerRon Strauss

    Cover ImageJoyce Haughey

    Cover DesignerMichael E. Trent

  • Introduction ...................................................................................................................................xxv

    Part I Getting StartedChapter 1: An Overview of CentOS .................................................................................................3Chapter 2: Installing CentOS ..........................................................................................................15Chapter 3: Getting Started with the Desktop .................................................................................69Chapter 4: Using Linux Commands .............................................................................................119

    Part II Using CentOSChapter 5: Accessing and Running Applications .........................................................................165Chapter 6: Publishing with CentOS .............................................................................................221Chapter 7: Music, Video, and Images in Linux ...........................................................................249Chapter 8: Using the Internet and the Web ................................................................................297

    Part III AdminstrationChapter 9: Understanding System Administration .......................................................................345Chapter 10: Setting up and Maintaining User Accounts .............................................................395Chapter 11: Automating System Tasks .........................................................................................427Chapter 12: Creating Backups and Restoring Data ......................................................................467Chapter 13: Security ..................................................................................................................... 505

    Part IV NetworkingChapter 14: Setting Up Network Connections and LANs ...........................................................561Chapter 15: Setting Up an Internet Connection ..........................................................................611Chapter 16: Setting Up Printers and Printing ..............................................................................657Chapter 17: Setting Up a File Server ............................................................................................679Chapter 18: Setting Up a Mail Server ...........................................................................................719Chapter 19: Setting Up an FTP Server .........................................................................................751Chapter 20: Setting Up a Web Server ..........................................................................................763Chapter 21: Setting Up an LDAP Address Book Server ...............................................................815Chapter 22: Setting Up a DHCP Boot Server ...............................................................................833Chapter 23: Setting Up a MySQL Database Server ......................................................................845Chapter 24: Making Servers Public with DNS .............................................................................879

    Appendix A: About the Media ......................................................................................................907

    Index ..............................................................................................................................................911

    ix

  • Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xxv

    Part I Getting Started

    Chapter 1: An Overview of CentOS . . . . . . . . . . . . . . . . . . . . . 3What You Get with CentOS .........................................................................................5Stepping Stone to Red Hat Enterprise Linux ...............................................................6

    What Is Linux? ......................................................................................................................7Linux’s Roots in UNIX .........................................................................................................7Common Linux Features ...................................................................................................10Primary Advantages of Linux ...........................................................................................11Going Forward with CentOS ............................................................................................12

    Help from the CentOS Project ....................................................................................12Training and Certification ...........................................................................................13Documentation ............................................................................................................13

    Summary ..............................................................................................................................14

    Chapter 2: Installing CentOS . . . . . . . . . . . . . . . . . . . . . . . . 15Using the CentOS Live CD ................................................................................................16Quick Installation ..............................................................................................................17Detailed Installation Instructions ...................................................................................18

    Installing CentOS 5 .....................................................................................................19Choosing Computer Hardware ...................................................................................21Preparing for Installation Using the Live CD .............................................................22Beginning the Installation ...........................................................................................25Running CentOS Firstboot ..........................................................................................32Going Forward after Installation .................................................................................34

    Special Installation Procedures .......................................................................................35Alternatives for Starting Installation ...........................................................................35Installing from Other Media .......................................................................................37Starting a VNC Install .................................................................................................40Performing a Kickstart Installation .............................................................................41

    xi

  • Contents

    Special Installation Topics ...............................................................................................46Setting up to Dual-Boot Linux and Windows ............................................................46Partitioning Your Disks ...............................................................................................52Using the GRUB Boot Loader .....................................................................................60

    Troubleshooting Installation ............................................................................................65Summary ..............................................................................................................................67

    Chapter 3: Getting Started with the Desktop . . . . . . . . . . . . . . . . 69

    Logging in to CentOS .........................................................................................................69Getting Familiar with the Desktop .................................................................................72

    Touring Your Desktop ................................................................................................72Tips for Configuring Your Desktop ............................................................................79

    Using the GNOME Desktop ..............................................................................................80Using the Metacity Window Manager ........................................................................81Using the GNOME Panels ...........................................................................................83Using the Nautilus File Manager ................................................................................88Changing GNOME Preferences ...................................................................................91Managing Removable Media .......................................................................................92Trying Other GNOME Applications ...........................................................................93Exiting GNOME ..........................................................................................................95

    Running 3D Accelerated Desktop Effects .......................................................................96Switching Desktop Environments ....................................................................................98Using the KDE Desktop .....................................................................................................98

    Starting with KDE .......................................................................................................99KDE Desktop Basics ..................................................................................................100Managing Files with the Konqueror File Manager ...................................................102Using the Konqueror Browser Features ....................................................................107Configuring Konqueror Options ...............................................................................107Managing Windows ...................................................................................................110Configuring the Desktop ...........................................................................................111Adding Widgets .........................................................................................................113

    Using the Xfce Desktop Environment ...........................................................................113Troubleshooting Your Desktop ......................................................................................114

    GUI Doesn’t Work at Startup ...................................................................................115Tuning Your Video Card and Monitor .....................................................................116Configuring Video Cards for Gaming .......................................................................118Getting More Information .........................................................................................118

    Summary ............................................................................................................................118

    Chapter 4: Using Linux Commands . . . . . . . . . . . . . . . . . . . . 119

    The Shell Interface ...........................................................................................................119Checking Your Login Session ...................................................................................120Checking Directories and Permissions .....................................................................121

    xii

  • Contents

    Checking System Activity .........................................................................................123Exiting the Shell ........................................................................................................125

    Understanding the Shell ..................................................................................................125Using the Shell in Linux .................................................................................................126

    Locating Commands ................................................................................................. 127Rerunning Commands ..............................................................................................129Connecting and Expanding Commands ...................................................................135Using Shell Environment Variables ..........................................................................138Managing Background and Foreground Processes ...................................................141Configuring Your Shell .............................................................................................143

    Working with the Linux File System ............................................................................147Creating Files and Directories ...................................................................................149Moving, Copying, and Deleting Files .......................................................................155

    Using the vi Text Editor ..................................................................................................155Starting with Vi .........................................................................................................156Moving around the File ............................................................................................159Searching for Text .....................................................................................................159Using Numbers with Commands .............................................................................160

    Summary ............................................................................................................................161

    Part II Using CentOS

    Chapter 5: Accessing and Running Applications . . . . . . . . . . . . . 165

    Getting and Installing Software Packages ...................................................................166Downloading and Installing Applications with yum ............................................... 167Getting CentOS Software Updates ............................................................................175

    Managing RPM Packages ................................................................................................176Using the Add/Remove Window ..............................................................................176Using the rpm Command .........................................................................................178

    Using Software in Different Formats ............................................................................188Understanding Software Package Names and Formats ............................................189Understanding Different Archive Formats ................................................................191Building and Installing from Source Code ...............................................................191

    Using CentOS to Run Applications ...............................................................................195Finding Common Desktop Applications in Linux ...................................................196Investigating Your Desktop .......................................................................................196Starting Applications from a Menu ...........................................................................198Starting Applications from a Run Application Window ..........................................198Starting Applications from a Terminal Window ......................................................199Running Remote X Applications ...............................................................................201

    Running Microsoft Windows, DOS, and Macintosh Applications ..........................205Running DOS Applications .......................................................................................207Running Microsoft Windows Applications in Linux ............................................... 209

    xiii

  • Contents

    Running Applications in Virtual Environments ..........................................................214Running Applications Virtually with Xen .................................................................214Running Applications Virtually with KVM and QEMU ...........................................218

    Summary ............................................................................................................................220

    Chapter 6: Publishing with CentOS . . . . . . . . . . . . . . . . . . . . 221

    Desktop Publishing in Linux ..........................................................................................222Using Text Editors and Notepads .............................................................................222Using Word Processors .............................................................................................222

    Using Traditional Linux Publishing Tools ...................................................................226Creating Documents in Groff or LaTeX ...................................................................227Text Processing with Groff ........................................................................................228Text Processing with TeX/LaTeX ..............................................................................231Converting Documents .............................................................................................233Creating DocBook Documents ..................................................................................234Understanding SGML and XML ...............................................................................235

    Displaying PDF Files with Evince .................................................................................238Doing Page Layout with Scribus ...................................................................................239Working with Graphics ...................................................................................................241

    Manipulating Images with GIMP ..............................................................................241Taking Screen Captures ............................................................................................243Creating Vector Graphic Images with Inkscape .......................................................244

    Using Scanners Driven by SANE ...................................................................................246Web Publishing .................................................................................................................247Summary ............................................................................................................................248

    Chapter 7: Music, Video, and Images in Linux . . . . . . . . . . . . . . 249

    Understanding Multimedia and Legal Issues in Linux ..............................................250Extending Freedom to Codecs ....................................................................................... 251Listening to Music in Linux ...........................................................................................251

    Configuring a Sound Card ........................................................................................253Choosing Audio Players ............................................................................................259Automatically Playing CDs ........................................................................................260Playing and Managing Music with Rhythmbox .......................................................261Playing Music with XMMS Audio Player .................................................................264Using ogg123, mpg321, and play Command-Line Players .....................................267Using MIDI Audio Players ........................................................................................268Converting Audio Files with SoX .............................................................................268Extracting and Encoding Music ................................................................................271Creating Your Own Music CDs ................................................................................274Creating CD Labels with cdlabelgen ........................................................................277

    Viewing TV and Webcams ..............................................................................................278Watching TV with Tvtime ........................................................................................279Videoconferencing and VOIP with Ekiga .................................................................281

    xiv

  • Contents

    Playing Video ....................................................................................................................285Examining Laws Affecting Video and Linux ............................................................285Understanding Video Content Types .......................................................................286Watching Video with Xine ........................................................................................288Using Totem Movie Player ........................................................................................292

    Using a Digital Camera ...................................................................................................293Displaying Images in gThumb ..................................................................................293Using Your Camera as a Storage Device .................................................................. 295

    Summary ............................................................................................................................296

    Chapter 8: Using the Internet and the Web . . . . . . . . . . . . . . . . 297Overview of Internet Applications and Commands ...................................................297Browsing the Web ............................................................................................................300

    Understanding Web Browsing ..................................................................................301Browsing the Web with Firefox ................................................................................305Setting Up Firefox .....................................................................................................308Using Text-Based Web Browsers ..............................................................................316

    Communicating with E-Mail ..........................................................................................317E-Mail Basics ............................................................................................................. 319Using Evolution E-Mail .............................................................................................320Thunderbird Mail Client ...........................................................................................322Text-Based Mail Programs .........................................................................................324

    Participating in Newsgroups ..........................................................................................326Instant Messaging with Pidgin .......................................................................................326Sharing Files with BitTorrent ........................................................................................328Using Remote Login, Copy, and Execution .................................................................329

    Using Telnet for Remote Login .................................................................................330Copying Files with FTP ............................................................................................331Getting Files with Wget ............................................................................................337Using ssh for Remote Login/Remote Execution .......................................................339Using scp for Remote File Copy ...............................................................................340Using the ‘‘r’’ Commands: rlogin, rcp, and rsh ........................................................341

    Summary ............................................................................................................................341

    Part III Adminstration

    Chapter 9: Understanding System Administration . . . . . . . . . . . . 345Using the root User Account ..........................................................................................346Becoming Super User (the su Command) ....................................................................346Learning about Administrative GUI Tools, Commands, Configuration

    Files, and Log Files .....................................................................................................348Using Graphical Administration Tools .....................................................................348Administrative Commands ........................................................................................353Administrative Configuration Files ...........................................................................354

    xv

  • Contents

    Administrative Log Files ...........................................................................................358Using Other Administrative Logins ..........................................................................358

    Administering Your Linux System .................................................................................360Configuring Hardware .....................................................................................................361

    Checking Your Hardware ..........................................................................................361Managing Hardware with HAL .................................................................................361Reconfiguring Hardware with kudzu .......................................................................362Configuring Modules .................................................................................................364

    Managing File Systems and Disk Space .......................................................................366Mounting File Systems ..............................................................................................369Using the mkfs Command to Create a File System .................................................377Adding a Hard Disk ..................................................................................................378Using RAID Disks ......................................................................................................381Checking System Space .............................................................................................382

    Monitoring System Performance ...................................................................................385Watch Computer Usage with System Monitor .........................................................385Monitoring CPU Usage with top ..............................................................................386Monitoring Power Usage on Laptop Computers ......................................................387

    Using Security Enhanced Linux .....................................................................................388Understanding Security Enhanced Linux .....................................................................389

    Types and Roles in SELinux .....................................................................................389Users in SELinux .......................................................................................................390Policies in SELinux ....................................................................................................390Tools in SELinux .......................................................................................................390

    Using SELinux in CentOS ...............................................................................................391SELinux .....................................................................................................................391Checking Whether SELinux Is On ...........................................................................392Checking SELinux Status ..........................................................................................393

    Summary ............................................................................................................................394

    Chapter 10: Setting up and Maintaining User Accounts . . . . . . . . . . 395

    Creating User Accounts ...................................................................................................395Adding Users with useradd .......................................................................................396Adding Users with User Manager .............................................................................400

    Setting User Defaults .......................................................................................................402Supplying Initial Login Scripts .................................................................................405Supplying Initial .bashrc and .bash_profile Files .....................................................406Supplying an Initial .tcshrc File ................................................................................407Configuring System-Wide Shell Options ..................................................................407Setting System Profiles ..............................................................................................408Adding User Accounts to Servers .............................................................................409

    Creating Portable Desktops ............................................................................................410Providing Support to Users ............................................................................................411

    xvi

  • Contents

    Creating a Technical Support Mailbox .....................................................................412Resetting a User’s Password ......................................................................................412

    Modifying Accounts .........................................................................................................413Modifying User Accounts with usermod ..................................................................413Modifying User Accounts with User Manager ..........................................................415

    Deleting User Accounts ...................................................................................................416Deleting User Accounts with userdel .......................................................................417Deleting User Accounts with User Manager .............................................................418

    Checking Disk Quotas .....................................................................................................418Using Quota to Check Disk Usage ...........................................................................418Using du to Check Disk Use ....................................................................................423Removing Temp Files Automatically ........................................................................423

    Sending Mail to All Users ...............................................................................................424Summary ............................................................................................................................425

    Chapter 11: Automating System Tasks . . . . . . . . . . . . . . . . . . 427

    Understanding Shell Scripts ...........................................................................................427Executing and Debugging Shell Scripts ....................................................................428Understanding Shell Variables ..................................................................................429Performing Arithmetic in Shell Scripts .....................................................................431Using Programming Constructs in Shell Scripts ......................................................432Some Useful External Programs ................................................................................438Trying Some Simple Shell Scripts .............................................................................439

    System Initialization ........................................................................................................441Starting init ................................................................................................................442The inittab File ..........................................................................................................442

    System Startup and Shutdown ......................................................................................446Starting Run-Level Scripts .........................................................................................447Understanding Run-Level Scripts .............................................................................447Understanding What Start-Up Scripts Do ................................................................450Changing Run-Level Script Behavior ........................................................................452Reorganizing or Removing Run-Level Scripts ..........................................................453Adding Run-Level Scripts .........................................................................................455Managing xinetd Services ..........................................................................................456Manipulating Run Levels .......................................................................................... 457

    Scheduling System Tasks ................................................................................................458Using at.allow and at.deny ....................................................................................... 458Specifying When Jobs Are Run ................................................................................ 458Submitting Scheduled Jobs .......................................................................................459Viewing Scheduled Jobs ............................................................................................460Deleting Scheduled Jobs ...........................................................................................460Using the batch Command .......................................................................................461Using the cron Facility ..............................................................................................461

    Summary ............................................................................................................................465

    xvii

  • Contents

    Chapter 12: Creating Backups and Restoring Data . . . . . . . . . . . . 467

    Making a Simple Backup Archive .................................................................................467Doing a Simple Backup with rsync ...............................................................................469

    Backing Up Files Locally ...........................................................................................469Backing Up Files Remotely .......................................................................................470

    Choosing Backup Tools ..................................................................................................472Selecting a Backup Strategy ...........................................................................................472

    Full Backup ...............................................................................................................473Incremental Backup ...................................................................................................473Disk Mirroring ...........................................................................................................473Network Backup ........................................................................................................474

    Selecting a Backup Medium ...........................................................................................474Magnetic Tape ...........................................................................................................474Writable CD Drives ...................................................................................................476Writable DVD Drives ................................................................................................480Writing CDs or DVDs with growisofs ......................................................................481

    Backing Up to a Hard Drive ...........................................................................................482Backing Up Files with dump ..........................................................................................483

    Creating a Backup with dump ..................................................................................484Understanding Dump Levels ....................................................................................486

    Automating Backups with cron .....................................................................................487Restoring Backed-Up Files ..............................................................................................488

    Restoring an Entire File System ................................................................................490Recovering Individual Files .......................................................................................491

    Configuring Amanda for Network Backups ................................................................493Creating Amanda Directories ....................................................................................494Creating the amanda.conf file ...................................................................................495Creating a disklist File ..............................................................................................497Adding Amanda Network Services ...........................................................................498Performing an Amanda Backup ................................................................................499

    Using the pax Archiving Tool ........................................................................................499Summary ............................................................................................................................503

    Chapter 13: Security . . . . . . . . . . . . . . . . . . . . . . . . . . . 505

    Linux Security Checklist .................................................................................................505Using Password Protection .............................................................................................508

    Choosing Good Passwords ........................................................................................508Using a Shadow Password File .................................................................................509

    Securing Linux with iptables Firewalls ........................................................................511Using the Security Level Configuration Window .....................................................512Configuring an iptables Firewall ...............................................................................513

    Controlling Access to Services with TCP Wrappers ..................................................525Checking Log Files ...........................................................................................................528

    xviii

  • Contents

    Replacing the sysklogd Package ................................................................................528Understanding the rsyslogd Service ..........................................................................528Tracking Log Messages with logwatch .....................................................................531

    Using the Secure Shell Package .....................................................................................532Starting the SSH Service ........................................................................................... 533Using the ssh, sftp, and scp commands ...................................................................533Using SSH, SCP, and SFTP without Passwords .......................................................535

    Securing Linux Servers ....................................................................................................536Understanding Attack Techniques ............................................................................536Protecting against Denial-of-Service Attacks ............................................................537Protecting against Distributed DOS Attacks .............................................................540Protecting against Intrusion Attacks .........................................................................544Securing Servers with SELinux .................................................................................548Protecting Web Servers with Certificates and Encryption .......................................548

    Summary ............................................................................................................................558

    Part IV Networking

    Chapter 14: Setting Up Network Connections and LANs . . . . . . . . . 561

    Connecting to the Network with NetworkManager ...................................................561Connecting to a Wireless Network ...........................................................................563Connecting to a Wired Network ..............................................................................563Setting Up a Virtual Private Network Connection ...................................................564

    Understanding Local Area Networks ............................................................................565Planning, Getting, and Setting Up LAN Hardware ..................................................566Configuring TCP/IP for Your LAN ...........................................................................571

    Setting Up a Wireless LAN .............................................................................................575Understanding Wireless Networks ...........................................................................576Choosing Wireless Hardware ....................................................................................577Getting Wireless Drivers ...........................................................................................582Installing Wireless Linux Software ...........................................................................584Configuring the Wireless LAN ..................................................................................584Testing Distances .......................................................................................................590Setting Wireless Extensions ......................................................................................590

    Understanding Internet Protocol Addresses ................................................................591IP Address Classes .....................................................................................................593Understanding Netmasks ..........................................................................................593Classless Inter-Domain Routing ................................................................................594Getting IP Addresses .................................................................................................596

    Troubleshooting Your LAN .............................................................................................597Did Linux Find Your Ethernet Driver at Boot Time? ..............................................597Can You Reach Another Computer on the LAN? ....................................................597Is Your Ethernet Connection Up? .............................................................................598

    xix

  • Contents

    Troubleshooting a Wireless LAN ..............................................................................600Watching LAN Traffic with Wireshark .....................................................................604

    Summary ............................................................................................................................609

    Chapter 15: Setting Up an Internet Connection . . . . . . . . . . . . . . 611Understanding How the Internet Is Structured ..........................................................611

    Internet Domains .......................................................................................................613Hostnames and IP Addresses ....................................................................................615Routing ......................................................................................................................616Proxies .......................................................................................................................617

    Using Dial-Up Connections to the Internet .................................................................617Getting Information ...................................................................................................617Setting Up Dial-Up PPP ............................................................................................618Creating a Dial-Up Connection with the Network Configuration Window ...........619Launching Your PPP Connection .............................................................................621Launching Your PPP Connection on Demand .........................................................621Checking Your PPP Connection ...............................................................................622

    Connecting Your LAN to the Internet ...........................................................................629Setting Up Linux as a Router .........................................................................................630

    Configuring the Linux Router ...................................................................................630Configuring Network Clients ....................................................................................633

    Configuring a Virtual Private Network Connection ...................................................634Understanding IPsec ..................................................................................................635Using IPsec Protocols ................................................................................................635Using IPsec in CentOS ..............................................................................................636Configuring an OpenVPN Server .............................................................................637

    Setting Up Linux as a Proxy Server ..............................................................................643Starting the Squid Daemon .......................................................................................644Using a Simple squid.conf File .................................................................................645Modifying the Squid Configuration File ...................................................................648Debugging Squid .......................................................................................................651

    Setting Up Proxy Clients .................................................................................................653Configuring Firefox to Use a Proxy ..........................................................................654Configuring Other Browsers to Use a Proxy ............................................................655

    Summary ............................................................................................................................655

    Chapter 16: Setting Up Printers and Printing . . . . . . . . . . . . . . . 657Common UNIX Printing Service ....................................................................................658Setting Up Printers .......................................................................................................... 658

    Using the Printer Configuration Window ................................................................659Using Web-Based CUPS Administration ..................................................................667Configuring the CUPS Server (cupsd.conf) ..............................................................670Configuring CUPS Printer Options ..........................................................................672

    Using Printing Commands ..............................................................................................673Using lpr to Print ......................................................................................................673

    xx

  • Contents

    Listing Status with lpc ...............................................................................................674Removing Print Jobs with lprm ................................................................................674

    Configuring Print Servers ...............................................................................................675Configuring a Shared CUPS Printer .........................................................................675Configuring a Shared Samba Printer ........................................................................676

    Summary ............................................................................................................................677

    Chapter 17: Setting Up a File Server . . . . . . . . . . . . . . . . . . . 679Goals of Setting Up a File Server ..................................................................................679Setting Up an NFS File Server .......................................................................................680

    Sharing NFS File Systems .........................................................................................682Using NFS File Systems ............................................................................................689Unmounting NFS File Systems .................................................................................694Other Cool Things to Do with NFS .........................................................................695

    Setting Up a Samba File Server .....................................................................................696Getting and Installing Samba ....................................................................................697Configuring a Simple Samba Server .........................................................................698Configuring Samba with SWAT ............................................................................... 701Working with Samba Files and Commands .............................................................710Setting Up Samba Clients .........................................................................................714Troubleshooting Your Samba Server ........................................................................715

    Summary ............................................................................................................................718

    Chapter 18: Setting Up a Mail Server . . . . . . . . . . . . . . . . . . . 719Introducing SMTP and Sendmail ..................................................................................719Installing and Running Sendmail ..................................................................................720

    Starting Sendmail ......................................................................................................721Other Programs .........................................................................................................722Logging Performed by Sendmail ...............................................................................722

    Configuring Sendmail ......................................................................................................724Getting a Domain Name ...........................................................................................725Configuring Basic Sendmail Settings (sendmail.mc) ................................................725Defining Outgoing Mail Access .................................................................................729Configuring Virtual Servers .......................................................................................731Configuring Virtual Users .........................................................................................732Adding User Accounts ..............................................................................................733Starting Sendmail and Generating Database Files ....................................................733Re-Directing Mail ......................................................................................................734

    Introducing Postfix ..........................................................................................................737Stopping Spam with SpamAssassin ..............................................................................738

    Using SpamAssassin ..................................................................................................738Setting Up SpamAssassin on Your Mail Server ........................................................739Setting E-Mail Readers to Filter Spam ......................................................................741

    Getting Mail from the Server (POP3 or IMAPv4) .......................................................741Accessing Mailboxes in Linux ...................................................................................742

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  • Contents

    Configuring IMAPv4 and POP3 with Dovecot .........................................................743Getting Mail from Your Browser with SquirrelMail ..................................................744Administering a Mailing List with Mailman ...............................................................746Summary ............................................................................................................................749

    Chapter 19: Setting Up an FTP Server . . . . . . . . . . . . . . . . . . 751Understanding FTP Servers ............................................................................................752

    Attributes of FTP Servers ..........................................................................................752FTP User Types .........................................................................................................753

    Using the Very Secure FTP Server .................................................................................753Quick-Starting vsFTPd ..............................................................................................754Configuring vsFTPd ..................................................................................................755

    Getting More Information about FTP Servers .............................................................761Summary ............................................................................................................................761

    Chapter 20: Setting Up a Web Server . . . . . . . . . . . . . . . . . . . 763Introduction to Web Servers ..........................................................................................764

    The Apache Web Server ...........................................................................................764Other Web Servers Available for CentOS ................................................................765

    Quick-Starting the Apache Web Server ........................................................................766Configuring the Apache Server ......................................................................................768

    Configuring the Web Server (httpd.conf) ................................................................769Configuring Modules and Related Services (/etc/httpd/conf.d/*.conf) ....................804

    Starting and Stopping the Server ..................................................................................806Monitoring Server Activities ...........................................................................................807

    Displaying Server Information ..................................................................................808Displaying Server Status ............................................................................................808Further Security of Server-Info and Server-Status ...................................................810Logging Errors ...........................................................................................................811Logging Hits ..............................................................................................................811Analyzing Web-Server Traffic ...................................................................................812

    Summary ............................................................................................................................814

    Chapter 21: Setting Up an LDAP Address Book Server . . . . . . . . . . 815Understanding LDAP .......................................................................................................816

    Defining Information in Schemas .............................................................................817Structuring Your LDAP Directories ..........................................................................819

    Setting Up the OpenLDAP Server ..................................................................................819Installing OpenLDAP Packages .................................................................................819Configuring the OpenLDAP Server (slapd.conf) ......................................................819Starting the OpenLDAP Service ................................................................................822

    Setting Up the Address Book .........................................................................................822More Ways to Configure LDAP ..................................................................................... 828Accessing an LDAP Address Book from Thunderbird ...............................................829Summary ............................................................................................................................831

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    Chapter 22: Setting Up a DHCP Boot Server . . . . . . . . . . . . . . . 833Using the Dynamic Host Configuration Protocol .......................................................834Setting Up a DHCP Server ..............................................................................................834

    Opening Your Firewall and SELinux for DHCP ......................................................835Configuring the /etc/dhcpd.conf File ........................................................................836Starting the DHCP Server .........................................................................................842

    Setting Up a DHCP Client ..............................................................................................843Summary ............................................................................................................................844

    Chapter 23: Setting Up a MySQL Database Server . . . . . . . . . . . . 845Finding MySQL Packages ...............................................................................................846Configuring the MySQL Server ......................................................................................848

    Using MySQL User/Group Accounts ........................................................................848Adding Administrative Users ....................................................................................848Setting MySQL Options ............................................................................................849Using Sample my.cnf Files ........................................................................................854

    Starting the MySQL Server .............................................................................................855Checking That MySQL Server Is Working ...................................................................856Working with MySQL Databases ..................................................................................857

    Starting the mysql Command ...................................................................................857Creating a Database with MySQL .............................................................................858Adding Data to a MySQL Database Table ................................................................860

    Understanding MySQL Tables .......................................................................................863Displaying MySQL Databases ........................................................................................868

    Displaying All or Selected Records ...........................................................................868Displaying Selected Columns ....................................................................................869Sorting Data ...............................................................................................................870

    Making Changes to Tables and Records ......................................................................871Altering the Structure of MySQL Tables ..................................................................871Updating and Deleting MySQL Records ...................................................................872

    Adding and Removing User Access ...............................................................................873Adding Users and Granting Access ..........................................................................873Revoking Access ........................................................................................................874

    Backing Up Databases ....................................................................................................875Checking and Fixing Databases ....................................................................................875Summary ............................................................................................................................877

    Chapter 24: Making Servers Public with DNS . . . . . . . . . . . . . . 879Determining Goals for Your Server ...............................................................................880

    Using a Hosting Service ............................................................................................880Connecting a Public Server ............................................................................................881

    Choosing an ISP ........................................................................................................881Getting a Domain Name ...........................................................................................884

    Configuring Your Public Server .....................................................................................886Configuring Networking ...........................................................................................886

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    Configuring Servers ...................................................................................................887Managing Security .....................................................................................................888

    Setting Up a Domain Name System Server .................................................................890Understanding DNS ..................................................................................................890DNS Name Server Example ......................................................................................894Quick-Starting a DNS Server ....................................................................................895Checking That DNS Is Working ...............................................................................903

    Getting More Information about BIND ........................................................................905Summary ............................................................................................................................905

    Appendix A: About the Media . . . . . . . . . . . . . . . . . . . . . . 907

    Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 911

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  • W ith the CentOS operating system and the instructions provided in this book, you cantransform your computers into free, safe, and powerful enterprise-class systems. Notonly can you configure your server to share files, printers, web pages, or directoryservices to other computers, but you can also use CentOS on everyday workstations as well tobenefit from its security and stability.

    Because CentOS includes enterprise-class software, the skills you learn by using CentOS can beapplied to work with the largest, most secure, and most diverse Linux systems in the world.Using this book is a great start for becoming a Linux professional.

    Who You AreYou don’t need to be a programmer to take advantage of this book. Perhaps you are someonewho just wants to use Linux to run programs, access the Internet, and so on. Or, perhaps youare someone who wants to learn how to administer an enterprise-grade Linux system.

    We assume that you are somewhat computer literate but may have little or no experience withLinux (or UNIX). You may be migrating from Microsoft operating systems to Linux because of itsnetworking and multiuser features. You may be looking to start a career as a computer technicianor network administrator and find that spending a few dollars for an entire operating system andbook is more economical than taking those technical classes offered on late-night television. Oryou might just think a ‘‘free’’ enterprise operating system is cool.

    This Book’s Learn-Through-Tasks ApproachThe best way to learn a computer system is to get your hands on it. To help you learn Linuxand CentOS, this book takes a task-oriented approach. Where possible, we step you through theprocess of working with a feature, such as setting up a network or configuring your desktop.

    When you are done with a task, you should have a good, basic setup of the feature that it covers.After that, we often provide pointers to further information on tweaking and tuning the feature.

    Instead of assuming that you already know about cryptic topics such as DNS, NFS, and TCP/IP,we ease you into those features with headings such as ‘‘Making Your Servers Public,’’ ‘‘Setting Up

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  • Introduction

    a File Server,’’ and ‘‘Connecting to the Internet.’’ If you already knew what all those things wereand how to get them working, you wouldn’t need us, would you?

    You will find that there are a lot of choices available in the Linux world. When many tools canbe used to achieve the same results, we usually present one or two examples. In other words,we don’t describe six different Web browsers, 12 different text editors, and three different mailservers. We tell you how to get one or two similar tools really working and then note that othersare available.

    What You NeedTo follow along with this book, you can install the complete CentOS 5 software found on theaccompanying DVD. If you don’t have a DVD drive, you can use the CD that comes with thisbook to try out CentOS without installing it. Of course, you can also follow along on an existingCentOS system.

    To install CentOS with the media that comes with this book, you need a PC with the followgeneral configuration:

    ■ An Intel Pentium or compatible CPU, 200 MHz Pentium or better (for text mode);400 MHz Pentium II or better (for GUI mode)

    ■ At least 64 MB of RAM (text-based install) or 128 MB of RAM (graphical install). To runthe GNOME or KDE desktops, 192 MB are needed, although the CentOS Project recom-mends at least 512 MB.

    ■ At least 3.0 GB of hard disk space for a typical workstation installation, or at least 1.1 GBof space for a server installation

    ■ A DVD or CD drive. This is recommended for installation (because an installation DVD isprovided along with this book), although you can install CentOS over a network or froma local hard disk instead. Chapter 2 describes methods of launching installations if youdon’t have a bootable DVD drive.

    Not every piece of PC hardware works with CentOS. You can see what hardware is supported byvisiting the following site: www.centoslinuxhcl.org.

    Conventions Used in This BookThroughout the book, special typography indicates code and commands. Commands and codeare shown in a monospaced font:

    This is how code looks

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  • Introduction

    In the event that an example includes both input and output, the monospaced font is still used,but input is presented in bold type to distinguish the two. Here’s an example:

    $ ftp ftp.example.comName (home:timothy): timothyPassword: *****

    The following boxes are used to call your attention to points that are particular important.

    A Note box provides extra information to which you need to pay special attention.

    A Tip box shows a special way of performing a particular task.

    A Warning box alerts you to take special care when executing a procedure, or damageto your computer hardware or software could result.

    A Cross-Reference box refers you to further information on a subject that you can findoutside the current chapter.

    How This Book Is OrganizedThis book is organized into four parts: Getting Started, Using CentOS, Administration, and Net-working.

    Part I: Getting StartedPart I consist of Chapters 1 through 4. Chapters 1 and 2 contain brief descriptions of the Linuxtechnology and tell you what you need to get the operating system installed. Chapter 1 servesas an introduction to the Linux OS and to CentOS in particular. Chapter 2 discusses what youneed to install CentOS and how to make the decisions you’ll be faced with during installation. Itincludes procedures for installing from DVD, hard disk, or network connections (NFS, FTP, orHTTP servers).

    In Chapter 3, you learn about the GNOME and KDE desktop environments. These GUIs providegraphical means of using CentOS. Chapter 4 describes ways of exploring and understandingCentOS primarily from the Linux shell command interpreter. You learn how to use the bashshell, the vi text editor, and the commands for moving around the Linux file system.

    Part II: Using CentOSPart II consists of Chapters 5 through 8, which include information for the average user whowants to use Linux to run applications and access the Internet.

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  • Introduction

    Chapter 5 contains information on obtaining, installing, and running Linux applications. It alsohelps you run applications from other operating systems in Linux. Chapter 6 describes bothold-time publishing tools and new, graphical word processors that are available with CentOS.Old tools include the troff and TeX text processing tools, whereas newer publishing softwareincludes OpenOffice.org (included on the DVD) and StarOffice (available commercially).

    Chapter 7 describes how to use audio and video players, as well as how to configure soundcards and CD burners. Chapter 9 describes tools for browsing the Web (such as the Firefox Webbrowser) and related tools (such as e-mail clients).

    Part III: AdministrationPart III consists of Chapters 9 through 13, which cover general set-up and system mainte-nance tasks, including how to set up user accounts, automate system tasks, and back up yourdata. Chapter 9, in which you learn what you need to know about basic system administration,describes the root login, administrative commands, configuration files, SELinux, and log files.Chapter 10 describes how to set up and provide support for multiple users on your CentOSsystem.

    In Chapter 11, you learn to create shell scripts and to use the cron facility to automate a varietyof tasks on your CentOS system. Techniques for backing up your system and restoring filesfrom backup are described in Chapter 12. Chapter 13 describes issues related to securing yourcomputing assets in CentOS.

    Part IV: NetworkingPart IV consists of Chapters 14 through 24, which describe step-by-step procedures for settingup a variety of server types. Simple configurations for what might otherwise be complex tasksare contained in each chapter. Learn to arrange, address, and connect your Linux computes toa local area network (LAN) in Chapter 14. Chapter 15 describes techniques for connecting yourCentOS computer and LAN to the Internet, using features such as Point-to-Point Protocol (PPP),IP forwarding, IP masquerading, routing, and proxy servers.

    Chapter 16 describes how to set up different types of print server interfaces, including Samba (toshare with Windows systems) and native Linux CUPS printing. Chapter 17 describes file servers,such as Network File System (NFS) servers and Samba file servers. Chapter 18 describes how toconfigure Sendmail or Postfix e-mail servers.

    Chapter 19 describes how to configure and secure an FTP server, as well as how to access theserver using FTP client programs. Chapter 20 teaches you how to set up CentOS as a Web Server,focusing on the popular Apache server software. Chapter 21 explains how to use LDAP to create ashared address book. Chapter 22 describes how to set up a DHCP server to distribute informationto client workstations on the network.

    Chapter 23 describes how to set up and use a MySQL database server in CentOS. Chapter 24takes you through the process of making the servers you configured in the other chapters avail-able on the Internet by setting up a Domain Name System (DNS) server.

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