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- Herausgeber: Packt Publishing
- Kategorie: Fachliteratur
- Sprache: Englisch
CentOS is a community-based enterprise class operating system and this book will provide a series of practical solutions that will not only show you how to install and maintain CentOS as a server, but to explore this well-known Linux distribution with the intention of tackling many common issues by providing some tricks of the trade in order to simplify the task of building a server."CentOS 6 Linux Server Cookbook" is a practical guide to installation, configuration, administration, and maintenance. This is a one-stop-shop to all things CentOS, so regardless as to whether you need a mail server, web server, database server, domain server or a file sharing platform, this book provides a comprehensive series of starting points that will give you direct access to the inner workings of this open source, community-based enterprise server."CentOS 6 Linux Server Cookbook" is a practical guide to the complete installation, configuration, administration, and maintenance of one of the world's most popular community-based enterprise servers.From installation to configuration, this book of recipes will take you on a journey to explore inner workings of CentOS server. Within this book you will learn how to install CentOS in variety of settings, enhance your installation with the correct tools of the trade and prepare your server to fulfil almost any role you could ever need.By discovering more about time, networking, package management, system management and security, this book will serve to show you how to get the very best from this freely available, open source server by presenting a series of solutions that will enable you to master the art of building your very own web, database, mail, domain name, file sharing services.CentOS 6 Linux Server Cookbook is a hands-on approach to installing, configuring and managing this ever popular community based enterprise server. By taking you from installation to customization this book will serve all Linux professionals and enthusiasts alike by providing you with a practical guide to using CentOS as a world-class server solution that is capable of delivering your mail, web, ftp, domain and file sharing services.
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Table of Contents
CentOS 6 Linux Server Cookbook
CentOS 6 Linux Server Cookbook
Copyright © 2013 Packt Publishing
All rights reserved. No part of this book may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, without the prior written permission of the publisher, except in the case of brief quotations embedded in critical articles or reviews.
Every effort has been made in the preparation of this book to ensure the accuracy of the information presented. However, the information contained in this book is sold without warranty, either express or implied. Neither the author, nor Packt Publishing, and its dealers and distributors will be held liable for any damages caused or alleged to be caused directly or indirectly by this book.
Packt Publishing has endeavored to provide trademark information about all of the companies and products mentioned in this book by the appropriate use of capitals. However, Packt Publishing cannot guarantee the accuracy of this information.
First published: April 2013
Production Reference: 1090413
Published by Packt Publishing Ltd.
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ISBN 978-1-84951-902-1
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Cover Image by Jasmine Doremus (<[email protected]>)
Credits
Author
Jonathan Hobson
Reviewers
Ugo Bellavance
Benoît Benedetti
Frank Lemmon
Acquisition Editor
Joanne Fitzpatrick
Lead Technical Editor
Dayan Hyames
Technical Editors
Dominic Pereira
Saijul Shah
Project Coordinator
Abhishek Kori
Proofreader
Mario Cecere
Indexer
Hemangini Bari
Production Coordinator
Shantanu Zagade
Cover Work
Shantanu Zagade
About the Author
Jonathan Hobson is a Web Developer, Systems Engineer, and Applications Programmer, who, for more than 20 years has been working behind the scenes to support companies, organizations, and individuals around the world to realize their digital ambitions. With an honors degree in both English and History and as a respected practitioner of many computer languages, Jonathan enjoys writing code, publishing articles, building computers, playing video games, and getting "out and about" in the big outdoors. He has been using CentOS since its inception and over the years, it has not only earned his trust, but it has become his first-choice server solution. CentOS is a first class community-based enterprise class operating system, it is a pleasure to work with, and because of this, Jonathan has written this book in order that his knowledge and experience can be passed on to others.
About the Reviewers
Ugo Bellavance, who has done most of his studies in e-commerce, started using Linux at Red Hat 5.2, got Linux training from Savoir-Faire-Linux at age 20, and got his RHCE on RHEL 6 in 2011. He's been a consultant in the past, but he's now an employee for a provincial government agency for which he manages the infrastructure (servers, workstations, network, security, virtualization, SAN/NAS, PBX). He's a big fan of open source software and its underlying philosophy. He's worked with Debian, Ubuntu, SUSE, but what he knows best is RHEL-based distributions. He's known for his contributions to the MailScanner project (he has been a technical reviewer for the MailScanner book), but also dedicated his time to different open source projects such as Mondo Rescue, OTRS, SpamAssassin, pfSense, and a few others.
I thank my lover, Lysanne, who accepted to allow me some free time slots for this review even with a two year-old and a six month-old to take care of. The presence of these three human beings in my life is simply invaluable.
I must also thank my friend Sébastien, whose generosity is only matched by his knowledge and kindness. I would never have reached that high in my career if it wasn't for him.
Benoît Benedetti works as a Linux System Administrator, for the University of Nice Sophia Antipolis, where he graduated with a degree in computer science.
He is always interested in resolving new problems, as it's an opportunity to work with new technologies. Benoît loves helping users, teaching students, and writing technical articles for GNU/Linux Magazine and GNU/Linux Pratique—the historical monthly magazines about Linux in France.
He would like to thank every person who dedicates their time developing free and open source software, and making them available for us to play with.
Frank Lemmon is a Senior Software QA Professional with seven years of CentOS experience. His past work experience includes working at Yahoo!, Qualys, Hewlett-Packard, and various other start-ups.
He worked as a reviewer on the first edition of the book, OWASP Developer's Guide.
In memory of my father, who valued the importance of education and was an inspiration to me.
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This book is dedicated to my family. I couldn't have done it without you.
Preface
Building a server can present a challenge. It is often difficult at the best of times and frustrating at the worst of times. They can represent the biggest of problems or give you a great sense of pride and achievement. Where the word "server" can describe many things, it is the intention of this book to lift the lid and expose the inner workings of this enterprise-class computing system with the intention of enabling you to build the professional server solution of choice.
CentOS is a community-based enterprise class operating system. It is available free of charge, and as a fully compatible derivative of Red Hat Enterprise Linux (RHEL) it represents the first choice operating system for organizations, companies, professionals, and home users all over the world who intend to run a server. It's widely respected as a very powerful and flexible Linux distribution and regardless as to whether you intend to run a web server, file server, FTP server, domain server, or a multi-role solution, it is the purpose of this book to deliver a series of turn-key solutions that will show you how quickly you can build a fully capable and comprehensive server system using the CentOS 6 operating system.
So with this in mind, you could say that this book represents more than just another introduction to yet another server-based operating system. This is a cookbook about an enterprise-class operating system that provides a step-by-step approach to making it work. So, regardless as to whether you are a new or an experienced user, there is something inside these pages for everyone, as this book will become your practical guide to getting things done and a starting point to all things CentOS.
What this book covers
Chapter 1, Installing CentOS, is a series of recipes that introduces you to the task of installing your server, updating, and enhancing the minimal install with additional tools and adding a desktop environment. It is designed to get you started and to provide a reference that shows you a number of ways to achieve the desired installation.
Chapter 2, Configuring CentOS, is designed to follow on from a successful installation to offer a helping hand and provide you with a number of recipes that will enable you to achieve the desired server configuration. From changing the time zone and updating the hardware clock to binding multiple IP addresses, you will not only learn how to resolve a fully qualified domain name but you will be shown how to work with multiple Ethernet devices and manage SELinux.
Chapter 3, Working with CentOS, provides the building blocks that will enable you to champion your server and take control of your environment. It is here to kick start your role as a server administrator, by disseminating a wealth of information that will walk you through a variety of steps that are required to develop a fully considered and professional server solution.
Chapter 4, Managing Packages with Yum, serves to introduce you to the definitive package manager for CentOS 6 server. From upgrading the system to finding, installing, removing, and enhancing your system with additional repositories, it is the purpose of this chapter to explain the open source command-line package management utility known as the Yellowdog Updater, Modified.
Chapter 5, Securing CentOS, discusses the need to implement a series of solutions that will deliver the level of protection you need to run a successful server solution. From escalating user privileges to preventing dictionary-based attacks, you will see how easy it is to build a server that not only considers the need to reduce risk from external attack but one that will provide additional protection for your users.
Chapter 6, Working with Samba, focuses on the power and simplicity of file sharing with Samba in order to provide CentOS 6 server with the ability to provide a sense of community within the workplace.
Chapter 7, Working with Domains, considers the steps required to implement domain names, domain resolution, and DNS queries on a CentOS 6 server. The domain name system is an essential role of any server and whether you are intending to support a home network or a full corporate environment, it is the purpose of this chapter to provide a series of solutions that will deliver the beginning of a future-proof solution.
Chapter 8, Working with Databases, provides a series of recipes that delivers instant access to MySQL and PostgreSQL with the intention of explaining the necessary steps required to deploy them on a CentOS 6 server.
Chapter 9, Providing Mail Services, introduces you to the process of enabling a domain-wide Mail Transport Agent to your CentOS 6 server. From building a local POP3/SMTP server to configuring SASL and dealing with SPAM, the purpose of this chapter is to provide the groundwork for all your future e-mail-based needs.
Chapter 10, Working with Apache, investigates the role of this well known server technology to full effect, and whether you are intending to run a development server or a live production server, this chapter provides you with the necessary steps to deliver the features you need to become the master of your web based publishing solution.
Chapter 11, Working with FTP, concentrates on the role of VSFTP with a series of recipes that will provide the guidance you need to install, configure and manage the File Transfer Protocol you want to provide on a CentOS 6 server.
What you need for this book
The requirements of this book are relatively simple and begin with the need to download the CentOS operating system. The software is free, but you will need a computer that is capable of fulfilling the role of a server, an Internet connection, some spare time, and a desire to have fun.
In saying that, many readers will be aware that you do not need a spare computer to take advantage of this book as the option of installing CentOS on virtualization software is always available. This approach is quite common and where the recipes contained within these pages remain applicable, you should be aware that the use of virtualization software is not considered by this book. For this reason any requests for support regarding this the use of this software should be directed towards the appropriate supplier.
Who this book is for
This is a practical guide for building a server solution, and rather than being about CentOS itself, this is a book that will show you how to get CentOS up and running. It is a book that has been written with the novice-to-intermediate Linux user in mind who is intending to use CentOS as the basis of their next server. However, if you are new to operating systems as a whole, then don't worry; this book will also serve to provide you with the step-by-step approach you need to build a complete server solution with plenty of tricks of the trade thrown in for good measure.
Conventions
In this book, you will find a number of styles of text that distinguish between different kinds of information. Here are some examples of these styles, and an explanation of their meaning.
Code words in text, database table names, folder names, filenames, file extensions, pathnames, dummy URLs, user input, and Twitter handles are shown as follows: "Again, if you experience any difficulties, simply check the logfile located at /var/log/maillog."
A block of code is set as follows:
Any command-line input or output is written as follows:
New terms and important words are shown in bold. Words that you see on the screen, in menus or dialog boxes for example, appear in the text like this: "The second step is to choose the button labeled Configure Network (located in the lower-left portion of the screen) and use the resulting Network Connections dialog box to record any changes to your Ethernet settings."
Note
Warnings or important notes appear in a box like this.
Tip
Tips and tricks appear like this.
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Chapter 1. Installing CentOS
In this chapter, we will cover:
Introduction
This chapter is a collection of recipes that will guide you through the process of un-wrapping the box and exploring a wide range of installation techniques by downloading CentOS and confirming the checksum on a Windows desktop; performing an installation of CentOS using the graphical installer; running a netinstall over HTTP; installing CentOS in Text Mode and building a minimal installation; re-installing the boot loader; updating the installation and enhancing the minimal install with additional administration and development tools; finishing the installation process with Firstboot; adding the GNOME desktop environment, changing the runlevel and installing additional software.
Downloading CentOS and confirming the checksum on a Windows desktop
In this recipe we will learn how to download and confirm the checksum of one or more CentOS 6 disk image(s) using a typical Windows desktop computer.
CentOS is made available in various formats by HTTP, FTP, or via a Torrent-based client from a series of mirror sites located across the world. It supports both the 32-bit and 64-bit architectures, and having downloaded one or more image files, it is often a good idea to validate those files' checksum in order to ensure that any resulting media should function and perform as expected.
Getting ready
To complete this recipe it is assumed that you are using a typical Windows-based computer (Windows 7, Windows Vista, or similar) with full administration rights. You will need an Internet connection to download the required installation files and access to a standard DVD/CD disk burner with the appropriate software in order to create the relevant installation disks.
How to do it...
Regardless as to what type of installation files you download, the following techniques can be applied to all image files supplied by the CentOS project:
Note
This URL was correct at the time of writing this book, but if it's no longer functional or is not available, then simply visit http://www.centos.org and navigate to Downloads | Mirrors | CentOS Public Mirror List or review the links associated with the latest release announcements made on the home page.
Note
As this is a standard text file, place your mouse on the link, right-click and choose Save As to download a copy of md5sum.txt. When finished, store this file in a safe place for future reference. For the purpose of this recipe, it is assumed that all downloads will be stored in your C:\Users\<username>\Downloads folder.
Note
If you are new to CentOS or are intending to follow the recipes found throughout this book, then the minimal installation is ideal. However, you should be aware that there are other options available to you.
For a full 64-bit DVD-based installation, you will need both:
CentOS-6.X-x86_64-bin-DVD1.iso
CentOS-6.X-x86_64-bin-DVD2.iso
For a full 32-bit DVD-based installation, you will need both:
CentOS-6.X-i386-bin-DVD1.iso
CentOS-6.X-i386-bin-DVD2.iso
For a minimal installation, you should choose either:
CentOS-6.X-i386-minimal.iso (32-bit version)
CentOS-6.X-x86_64-minimal.iso (64-bit version)
For a network installation, you should choose either:
CentOS-6.X-i386-netinstall.iso (32-bit version)
CentOS-6.X-x86_64-netinstall.iso (64-bit version)
If you choose to download a torrent file, then you will need to extract these files in the usual way in order to build the appropriate ISO image file(s).
Note
The full URL is http://mirror.centos.org/centos/dostools/md5sum.exe.
Note
For example, you can type md5sum.exe CentOS-6.X-x86_64-minimal.iso
How it works…
The act of downloading an installation image and validating the file's integrity is just the first step towards building the perfect server, and although the process of downloading CentOS is very simple, many do forget the need to confirm the checksum.
So what have we learned from this experience?
We began this recipe by showing you how to download CentOS by outlining the various options available to you. It is not expected that you will need to do this often, but during the course of this recipe you also learned how to navigate the CentOS Project website and select the best download location based on your current location.
Having done this, our next step was to obtain a copy of md5sum.txt before downloading the preferred image files.
Note
The choice as to whether you selected a 32-bit or 64-bit version is largely dependent on the specification of your intended server. However, given the abilities of most modern computers, for most people the obvious choice will be the 64-bit version in order that you can take advantage of the improved code base and support more than 4 GB of RAM.
The time required to complete the task of downloading the relevant files will depend largely on the speed of your Internet connection, but it was important that we obtained a copy of md5sum.exe in order to confirm file integrity and compare the value given against those listed in md5sum.txt.
The DOS-based tool was obtained from http://mirror.centos.org/centos/dostools/md5sum.exe.
Having completed these steps, we then proceed to open a command prompt session and navigate to the expected destination of all the files by typing:
We then proceeded to view the contents of C:\Users\<username>\Downloads by typing the following command:
This action lists the filenames concerned, thereby enabling us to modify the following command in order to validate the appropriate ISO files:
The resulting response provides us with the checksum value of the file in question in order that we can compare it with the corresponding value found in md5sum.txt.
For example, the content of md5sum.txt may look like this:
Whereas the display in command prompt may show:
You should repeat this process for all image files, and if these values match, then you can be confident that your download is verified. A fact that not only reduces the chance of wasting optical disks, but with security in mind, it also implies that what you downloaded is what you were expecting to download (and not something else).
So remember, with every new release the CentOS team will update the main website and enable you to download the required image files. Unless the CentOS project states otherwise, you will only need to do this once, as all minor updates can be managed like any other operating system (discussed later in this book). However, if you do intend to download them again, then it is always a good idea to check the integrity of your image files with the md5sum checksum tool.
See also
Performing an installation of CentOS using the graphical installer
In this recipe we will learn how to perform a typical installation of CentOS using the graphical tools provided by the system installer.
In many respects this is considered to be the recommended approach to installing your system as it not only provides you with the chance to create the desired hard disk partitions, but also provides the ability to customize package selection. Your installation will then form the basis of a server on which you can build, develop, and run any type of service you may want to provide in the future.
Getting ready
Before we begin, it is assumed that you have followed a previous recipe in which you were shown how to download CentOS, confirm the checksum of the relevant image files, and create the relevant installation disks.
Depending on which installation image(s) were downloaded, in order to complete this recipe you will be expected to have completed the initial stages of a network install or that you are using one of the following DVD suites:
In addition to this, you should be confident that your server can meet the following minimum specifications:
Of course, it should be said that the preceding specification acts as guidance only and further details concerning the minimum system requirements can be found at the end of this recipe.
Note
For a typical server you should always consider the need to maximize your resources in terms of RAM and available hard disk space. You should also plan for the long term. Remember, the use of a 64-bit capable CPU will not only tend to run faster with a 64-bit operating system but the system as a whole will be able to take advantage of more than 4 GB of RAM and therefore provide a long-term, scalable solution that can grow with the needs of your network.
How to do it...
To begin this recipe, start by booting your computer from the first CentOS installation DVD and wait for the welcome screen:
Note
You should be aware that the verification process performed during this phase will not always guarantee a trouble-free installation as it will not monitor hardware or measure environmental conditions. This feature is not always used, but it can serve to increase the frequency of success by checking the file integrity of your installation media.
Note
If you are using a new hard disk or a virtual disk, you may see what could be described as a warning/error message. The message may read:
The storage device below may contain data
Don't worry, this is to be expected and the message is simply asking you to initialize your hard disk because it is considered to be blank, unpartitioned, or a virtual drive. In most cases, especially if you have more than one hard drive, simply enabling the checkbox and choosing yes, discarding any data will complete the task of disk initialization and enable you to proceed to the next step.
On the other hand, and should you feel inclined to do so, you can take this opportunity to explore the individual packages found on your installation media by choosing to customize the software selection. To do this, simply check the box labeled Customize Now before leaving this screen.
When you are ready, click Next to proceed.
CentOS will now resolve any dependencies and the installer will begin writing to the hard disk. This may take some time, but a progress bar will indicate the status of your installation. When finished, the congratulations screen will inform you that the entire process is complete and that the installation was successful. So when you are ready, click Reboot to finalize this recipe and to recover the installation media. Congratulations, you have now installed CentOS 6.How it works…
In this recipe you have discovered how to install the CentOS 6 operating system, and having covered the typical approach to the graphical installation process you are now in a position to develop the server with additional configuration changes and packages that will suit the role you intend the server to fulfill.
So what have we learned from this experience?
We started by initializing the main installer and determining whether we would like to check the installation media for possible corruption and defects. Of course, validating the data on your disk is always a useful process and it can save time in the long run, but you should be aware that it will not necessarily guarantee a trouble-free installation. For this reason, most users who have already validated the checksum tend to skip this process.
The next steps then welcomed us to CentOS and invited us to confirm the appropriate language, keyboard, location, hostname, root password, network, and storage settings.
For example, any changes to the language setting were immediate, whereas the configuration of your network settings was simply a matter of ensuring the Ethernet device would connect automatically and modifying the appropriate IPv4/IPv6 settings. You were able to create a static or dynamic IP address, while the setting of a root password was simply a matter of choosing an appropriate series of alpha-numeric values that did not consist of known words, typical phrases, or contain any whitespace. Whatever password you decide on, it should consist of no less than six characters to avoid any warnings issued by the installer.
During the next stage, we then considered the need to partition the hard disks by selecting the default option known as Use All Space. By choosing this option, you were allowing the installer to determine the relative sizes of each partition and to build a logical volume that would assign GRUB to a default location. Of course, diving in to the depths of partition management was beyond the purpose of this recipe, but you did see that the various options that enable you to build your own custom layout should this be the preferred option.
You were then given the option to change the location of GRUB. This is not always deemed to be necessary, as moving GRUB can be an awkward process for even the most experienced users but ignoring this, you did discover an option that would enable you to password-protect the boot loader and provide additional system-wide protection.
Finally we came upon the package group selection screen where we discovered that CentOS not only enables us to choose a minimal install, but it also provides for a significant number of package selection groups that are designed for convenience.
The sole purpose of these groups is to simplify the process of selecting the correct packages for your installation. I think you would agree that most of the group titles are self-explanatory, but it is generally accepted that a minimal install is by far the most efficient method of installing any server because it is far easier to add and configure packages when we need them rather than simply installing everything at once. This rule of thumb not only reduces your initial workload, but it also ensures that your server remains safe and secure which is of a particular concern if it is located in the public domain.
So in conclusion, I think it would be appropriate to say that there is always more to discover about the installation process and that there are many different ways to install your server, but at this early stage you should now take the time to sit back and relax. Well done, you have now completed the recommend installation process and yes, you can now install CentOS.
See also
Running a netinstall over HTTP
In this recipe we will learn how to initiate the process of running a netinstall over HTTP (using the URL method) in order to install CentOS 6.
The CentOS network installation is a process by which a small image file is used to boot the computer and enable the download of all the necessary files that will be required to complete the installation of the full operating system.
Using this approach implies the advantage of not being required to download the DVD-based image files and for computers that do not have access to DVD drive; this can be of enormous benefit. Moreover, where you will only download the packages you need, unless you are intending to install more than one server then the entire netinstall-based approach (starting from downloading the initial installation image to finalizing the installation of your computer) not only provides greater flexibility, but it will also save time and offers the benefit of the full installer.
Getting ready
Before we begin, it is assumed that you have followed a previous recipe in which you downloaded the netinstall image of Centos 6, confirmed the checksum values of the image file, and that you have already created the relevant installation disk.
To complete this recipe you will need an active Internet connection, and because this recipe will serve as a starting point to the graphical installation process, you should be confident that your server can meet the following minimum requirements:
Note
You should be aware that these specifications act as guidance only and further details concerning the minimum system requirements can be found at http://wiki.centos.org/About/Product.
How to do it...
To begin this recipe, insert the netinstall disc, boot your computer from the optical drive, and wait for the welcome screen to appear:
Note
You should be aware that the verification process performed during this phase will not always guarantee a trouble-free installation as it cannot monitor hardware or measure environmental conditions. This feature is not always used but it can serve to increase the frequency of success by checking the file integrity of your installation media.
Note
If you have elected to use a static IP address you will be presented with the Manual TCP/IP Configuration screen. This implies that you will be expected to confirm your IP address, Netmask, Gateway, and Nameserver (or DNS) settings by typing in the respective values as required. When you are finished, highlight OK and press the Return key to proceed.
Tip
Remember, if you need to enable an HTTP proxy, do this now by entering the relevant details. If you are in doubt, know that you do not use a Proxy or you are unaware of such a feature on your network then leave this section blank.
Alternatively, you can also use a personal repository on your local network should you have access to such a facility.
When you are ready, by using the Tab key, highlight OK and press the Return key to proceed.
On success, the installer will begin to retrieve the appropriate install.img file. This may take several minutes to complete, but once resolved a progress bar will then indicate all the download activity. When this process has finished, the installer will prepare the onscreen environment and present you with the installation welcome screen.Note
From this point onwards you will be able to install CentOS using the graphical installer in the usual way but with one difference. Having resolved the necessary package dependencies all required packages will be downloaded from the Internet.
How it works...
The purpose of this recipe was to introduce you to the concept of the CentOS network installation process in order to show you just how simple this approach can be. By completing this recipe you have not only saved time by limiting your initial download to those files required by the installation process, but you have been able to take advantage of the full graphical installation method without the need for a complete DVD suite.
So what have we learned from this experience?
We have learned how to boot from the netinstall image, initialize the main installer, test the optical media for errors, provide the relevant network settings for the host computer, and provide a URL in order to download the relevant files.
The URL in this case was web-based and dependent on the preferred architecture, but as an alternative you could have modified this instruction to use a local mirror site or even implement an installation from a local repository from your local network.
So in conclusion, it must be said that if you are intending to install more than one server at a time (with a full array of packages), then this may not be the best approach, but for a single server or multiple servers using a minimal install, then the netinstall image represents a far more flexible approach. Rather than waiting to download a complete set of installation files you may never need, the installer will download the required files directly from the chosen location thereby ensuring that you will not only reduce the overall time it takes to get your server up and running, but you will be able to take advantage of the full installation without the need for a DVD drive.
See also
Installing CentOS in Text Mode and building a minimal installation
In this recipe we will learn how to install CentOS in Text Mode.
For new users, Text Mode may not be the first choice when deciding how to install your server but it does remain a popular and useful option for a variety of reasons.
Installing a system in Text Mode offers reduced
