Linux Apache Web Server Administration Charles Aulds SYBEX® This page intentionally left blank This page intentionally left blank Linux Apache Web Server Administration Charles Aulds San Francisco Paris Düsseldorf Soest London Associate Publisher: Neil Edde Contracts and Licensing Manager: Kristine O’Callaghan Acquisitions and Developmental Editor: Maureen Adams Editor: James A. Compton Production Editor: Dennis Fitzgerald Technical Editor: Will Deutsch Book Designer: Bill Gibson Graphic Illustrator: Eric Houts, epic Electronic Publishing Specialist: Franz Baumhackl Proofreaders: Erika Donald, Nathan Whiteside Indexer: Jack Lewis Cover Designer: Ingalls & Associates Cover Illustrator/Photographer: Ingalls & Associates Copyright © 2001 SYBEX Inc., 1151 Marina Village Parkway, Alameda, CA 94501. World rights reserved. No part of this publication may be stored in a retrieval system, transmitted, or reproduced in any way, includ- ing but not limited to photocopy, photograph, magnetic, or other record, without the prior agreement and written permission of the publisher. Library of Congress Card Number: 00-106196 ISBN: 0-7821-2734-7 SYBEX and the SYBEX logo are either registered trademarks or trademarks of SYBEX Inc. in the United States and/or other countries. Screen reproductions produced with FullShot 99. FullShot 99 © 1991-1999 Inbit Incorporated. All rights reserved. FullShot is a trademark of Inbit Incorporated. Netscape Communications, the Netscape Communications logo, Netscape, and Netscape Navigator are trademarks of Netscape Communications Corporation. Netscape Communications Corporation has not authorized, sponsored, endorsed, or approved this publica- tion and is not responsible for its content. Netscape and the Netscape Communications Corporate Logos are trademarks and trade names of Netscape Communications Corporation. All other product names and/or logos are trademarks of their respective owners. TRADEMARKS: SYBEX has attempted throughout this book to distinguish proprietary trademarks from descriptive terms by following the capitalization style used by the manufacturer. The author and publisher have made their best efforts to prepare this book, and the content is based upon final release software whenever possible. Portions of the manuscript may be based upon pre-release versions supplied by software manufacturer(s). The author and the publisher make no representation or warranties of any kind with regard to the completeness or accuracy of the contents herein and accept no liability of any kind including but not limited to performance, merchantability, fitness for any particular purpose, or any losses or damages of any kind caused or alleged to be caused directly or indirectly from this book. Manufactured in the United States of America 10 9 8 7 6 5 4 3 2 1 Foreword Linux and open-source software are synonymous in the minds of most people. Many cor- porations fear Linux and reject it for mission-critical applications because it is open source. They mistakenly believe that it will be less secure or less reliable because the code is openly available and the system has been developed by a diverse collection of groups and individuals from around the world. Yet those same organizations depend on open- source systems every day, often without being aware of it. The Internet is a system built on open-source software. From the very beginning, when the U.S. government placed the source code of the Internet Protocol in the public domain, open-source software has led the way in the development of the Internet. To this day, the Internet and the applications that run on it depend on open-source software. One of the greatest success stories of the Internet is the World Wide Web—the Internet’s killer application. The leading Web server software is Apache, an open source product. No library of Linux system administration books could be complete without a book on Apache configuration and administration. Linux and Apache are a natural combination—two reliable, powerful, open source prod- ucts that combine to create a great Web server! Craig Hunt September 2000 Acknowledgments If I ever believed that a technical book was the work of a single author, I no longer hold that belief. In this short section, I would like to personally acknowledge a few of the many people who participated in writing this book. A lot of credit goes to the Sybex production and editing team, most of whom I didn’t work with directly and will never know. Craig Hunt, editor of this series, read all of the material and helped organize the book, giving it a continuity and structure that brings together all of the many pieces of the Apache puzzle. Before I met Craig, however, I knew Maureen Adams, the acquisition editor who recommended me for this book. Her confidence in my ability to accomplish this gave me the resolve to go further than simply saying, “I believe that some day I might write a book.” Associate Publisher Neil Edde’s can-do attitude and problem-solving skills also helped the project over a few bumps in the road. Also part of the Sybex team, production editor Dennis Fitzgerald kept the project on schedule. Many times, prioritizing a long list of things that needed to be done is the first step toward their accomplishment. Jim Compton, editor, provided invaluable editing assistance, and often surprised me with his keen grasp of the technical material, many times suggesting changes that went far beyond the merely syntactic or grammatical. Will Deutsch was the technical editor for this book, and his research background and experi- ence filled in more than a few gaps in my own store of knowledge. Electronic publishing specialist Franz Baumhackl handled the typesetting and layout promptly and skillfully, as usual. I must thank my employer, Epic Data — Connectware Products Group, for allowing me the freedom to work on this book. Particular thanks go to Linda Matthews, who was my supervisor during most of the project. I also appreciate the time my keen engineering friend, Carl Sewell, spent reviewing all of the material I’d written, and I thank my Epic colleague Robert Schaap, whose knowledge of Apache and comments on the use of the mod_rewrite module proved quite valuable. Last, but certainly most of all, I want to thank my dear wife, Andrea, for her unwavering support during what turned out to be a much harder endeavor than I anticipated. Finding time to devote to this project was the biggest challenge I had to overcome, and she found ways to give me that, taking on many of the household and outdoor chores that had been my responsibility. Contents at a Glance Introduction. . . . . . . . . . . . . . . . . . . . . . . xviii Part 1 How Things Work 1 Chapter 1 An Overview of the World Wide Web . . . . . . . . . . . . . 3 Chapter 2 Apache and Other Servers . . . . . . . . . . . . . . . . . 29 Part 2 Essential Configuration 43 Chapter 3 Installing Apache . . . . . . . . . . . . . . . . . . . . 45 Chapter 4 The Apache Core Directives . . . . . . . . . . . . . . . . 81 Chapter 5 Apache Modules . . . . . . . . . . . . . . . . . . . .127 Chapter 6 Virtual Hosting . . . . . . . . . . . . . . . . . . . . .145 Part 3 Advanced Configuration Options 171 Chapter 7 Server-Side Includes . . . . . . . . . . . . . . . . . . .173 Chapter 8 Scripting/Programming with CGI and Perl . . . . . . . . . . . .207 Chapter 9 Other Apache Scripting/Programming Tools . . . . . . . . . . .273 Chapter 10 Aliasing and Redirection . . . . . . . . . . . . . . . . .325 Chapter 11 Controlling Apache . . . . . . . . . . . . . . . . . . .363 Part 4 Maintaining a Healthy Server 387 Chapter 12 Apache Logging . . . . . . . . . . . . . . . . . . . .389 Chapter 13 Proxying and Performance Tuning . . . . . . . . . . . . . .421 Chapter 14 Basic Security for Your Web Server . . . . . . . . . . . . . .453 Chapter 15 Secure Sockets Layer . . . . . . . . . . . . . . . . . .481 Chapter 16 Metainformation and Content Negotiation . . . . . . . . . . .509 Appendices 533 Appendix A Apache Directives . . . . . . . . . . . . . . . . . . . .535 Appendix B Online References . . . . . . . . . . . . . . . . . . .549 Appendix C Transferring Files to Apache . . . . . . . . . . . . . . . .565 Appendix D Using Apache Documentation Effectively . . . . . . . . . . . .583 Index . . . . . . . . . . . . . . . . . . . . . . . . . .590 Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . xviii Part 1 How Things Work 1 Chapter 1 An Overview of the World Wide Web . . . . . . . . . . 3 A Brief History of the WWW . . . . . . . . . . . . . . 3 How the Web Works . . . . . . . . . . . . . . . . 7 What Is a Web Server? . . . . . . . . . . . . . . 9 The HTTP Protocol . . . . . . . . . . . . . . . . 10 New Features in HTTP/1.1 . . . . . . . . . . . . 12 HTTP Request Methods . . . . . . . . . . . . . 13 Observing the HTTP Protocol in Action . . . . . . . . 14 In Sum . . . . . . . . . . . . . . . . . . . . 27 Chapter 2 Apache and Other Servers . . . . . . . . . . . . . 29 Who Are the Major Players? . . . . . . . . . . . . . 30 Alternatives to Apache . . . . . . . . . . . . . . . 30 The Free Servers . . . . . . . . . . . . . . . 31 The Commercial Variety . . . . . . . . . . . . . 32 The Features of Apache . . . . . . . . . . . . . . 35 Further Benefits . . . . . . . . . . . . . . . 37 The Architecture of Apache . . . . . . . . . . . . . 38 New Features of Apache Version 2.0 . . . . . . . . . 40 In Sum . . . . . . . . . . . . . . . . . . . . 41 Part 2 Essential Configuration 43 Chapter 3 Installing Apache . . . . . . . . . . . . . . . . 45 The Decision to Compile . . . . . . . . . . . . . . 45 Downloading Apache Source . . . . . . . . . . . . . 48 Compiling Apache . . . . . . . . . . . . . . . . 49 Using APACI . . . . . . . . . . . . . . . . 50 The configure Script . . . . . . . . . . . . . . 50 The config.status File . . . . . . . . . . . . . 54 Contents ix The config.layout File . . . . . . . . . . . . . 56 Making Apache . . . . . . . . . . . . . . . . 62 Installing the Apache Binaries . . . . . . . . . . . . . 64 Which Modules Are Included? . . . . . . . . . . . 64 Red Hat Package Manager . . . . . . . . . . . . 67 Binary Distributions . . . . . . . . . . . . . . 71 Running the Server . . . . . . . . . . . . . . . . 74 Using Apachectl . . . . . . . . . . . . . . . . 78 Running Multiple Apache Servers . . . . . . . . . . 78 In Sum . . . . . . . . . . . . . . . . . . . . 80 Chapter 4 The Apache Core Directives . . . . . . . . . . . . . 81 Using Apache Directives . . . . . . . . . . . . . . . 82 The All-Powerful httpd.conf File . . . . . . . . . . 83 Securing Obsolete Configuration Files . . . . . . . . . 84 Directive Scope and Context . . . . . . . . . . . . . 84 Defining the Main Server Environment . . . . . . . . . . 85 The ServerName Directive . . . . . . . . . . . . . 86 The ServerRoot Directive . . . . . . . . . . . . . 86 The DocumentRoot Directive . . . . . . . . . . . . 87 The ScriptAlias Directive . . . . . . . . . . . . 87 More General-Server Directives . . . . . . . . . . . . 88 The ErrorDocument Directive . . . . . . . . . . . . 88 The DefaultType Directive . . . . . . . . . . . . 89 Controlling Server Processes . . . . . . . . . . . . 89 Defining How the Server Listens for Connections . . . . . . . 92 The BindAddress Directive . . . . . . . . . . . . 93 The Port Directive . . . . . . . . . . . . . . . 93 The Listen Directive . . . . . . . . . . . . . . 94 The Options Directive . . . . . . . . . . . . . . . 95 The Container Directives . . . . . . . . . . . . . . 97 The <VirtualHost> Container . . . . . . . . . . . 97 The <Directory> and <DirectoryMatch> Containers . . . . 98 The <Files> and <FilesMatch> Containers . . . . . . .101