Chapter 01

Introducing Package Management

Copyright (c) 2005 by Eric Foster-Johnson. This material may be distributed only subject to the terms and conditions set forth in the Open Publication License, v1.0 or later (the latest version is presently available at http://www.opencontent.org/openpub/).

In This Chapter

*	Issues in software management

*	Examining Linux management tools

*	Introducing the package concept

In 1991, a young Finnish graduate student started a new personal hobby. He had acquired an Intel 386 computer and had spent a few weeks exploring it and playing early PC computer games. Eventually, however, he grew bored with the limitations of the MS-DOS environment that had come with his toy and decided that he wanted an operating system for it that he could use more productively. After exploring Minix, a feature-limited teaching operating system, he decided he needed a full-featured OS.

At that time, no full-featured PC operating systems were freely available, so he decided to write his own operating system. Today, that small hobby OS that Linus Torvalds started almost as a whim has become Linux (www.linux.com), a significant new variant of Unix that runs millions of the world's network servers and, increasingly, desktop computers and embedded processors.

Linux has grown up, successfully making the transition from a one-man personal project to a functional, full-featured operating system used by many of the world's major corporations and deployed on millions of corporate and personal systems. Along the way, Linux has had to address many of the same issues any new operating system must face. One of these concerns is how software for Linux, and how the Linux operating system itself, should be installed. How can administrators safely remove software packages without affecting other installed packages? And how can you safely upgrade packages? Answering these questions is what this book is all about.

Installing, Removing, and Upgrading Applications

Applications for most operating systems consist of multiple files that must be copied to specific locations on the computer's file system before each application can be run. This is true for common PC operating systems such as MS-DOS or Microsoft Windows, as well as for Unix and Linux.

In the case of a Unix-like operating system such as Linux, other issues must also be considered. Unix and Linux are multiple-user systems, so they must track ownership of files. Furthermore, Unix and Linux use a system of file permissions. Administrators can grant some users access to files and can control how users may access those files, for example, allowing some users the permission to read only certain files. Administrators can deny other users access to the same files. So, installation of an application on Linux requires consideration of all these details. After files are copied into their appropriate locations, they must be granted correct permissions and correct ownerships.

Similarly, administrators occasionally need to remove installed software from the computer. Maybe the program is no longer needed; maybe it does not work correctly for the needed task, or maybe the space it is using is needed for more important programs. In addition, installed software sometimes needs to be upgraded. Perhaps a new version of the software has come out and the currently installed version needs to be replaced with the presumably improved version. In most respects, software upgrades are the same as the removal of one application (the old version), followed by installation of another application (the new version). Upgrades do, however, have additional issues. Many applications must be configured before they can be used. Ideally, the upgrade for an installed application takes the current configuration into account, preserving old configuration information and applying it to the recently installed version.

All these considerations make installation of a new application onto Unix or Linux a labor-intensive process. To further complicate matters, Unix applications have primarily been distributed as source code. To install a new application, such as the Apache Web server, you download the source code for that application—in this case, from the Apache Project's Web page (http://httpd.apache.org). Typically, the source code is provided in some sort of archive (such as the Zip archival and compression format often used in the Windows world or the tar archive format typically used in the Unix world) that you must then unpack. After unpacking this source code, you have to configure it to support the options and systems you want, compiling it to produce an executable program that can run on your particular operating system (CPU combination).

After compiling the source code, you still have to install the application by putting all of its components (executable programs, documentation, configuration files, and so forth) into the correct locations on your hard drive and setting correct permissions on all those files. You might also need to perform other steps to prepare the system for the software. In the case of Apache, for example, some space needs to be set aside for storage of Web-access logs, and a special user account needs to be created so that the Apache Web server can operate more securely. Finally, you are ready to try running the application you have spent so much time installing.

To help with all these tasks, precompiled software is becoming increasingly prevalent in the Unix and Linux communities, so you might be able to find executable (precompiled binary) copies of the application you wish to install that are appropriate for your particular machine's CPU. In that case, download an archive of the compiled application and unpack it. Then skip the compilation step, since that has already been done for you. The other steps required to install the package (copying files into correct locations, setting file permissions, and doing any needed system or application configuration) are exactly the same as the steps performed to install that application from source code. Once those steps are finished, you are ready to test your freshly installed application.

When you run your newly installed application, you might be thrilled, perhaps discovering that it is something you want to use regularly. On the other hand, you might discover that you have no use for the software you have just installed, deciding that you want to uninstall it.

Uninstallation occurs by reversing the installation steps. Remember any special steps you have performed (such as adding a user account), and undo those. Then remember all the files you have installed and where you have installed them. Manually delete them. As you can see, this can become a pretty tedious exercise.

If you like the application you have installed, you will likely find yourself wanting to upgrade it eventually. The Apache Web server, for example, like any network service, must be upgraded whenever security problems are found and fixed. If you find that you need to upgrade Apache, you need to back up your Apache configuration files and then uninstall Apache. The next step is to install a new version of Apache, applying your Apache-configuration customizations to your new installation of Apache.

All of this is a big pain. There has to be a better way. And there is.

Overcoming the Installation Obstacles

None of the tasks you must perform to install, upgrade, or uninstall applications are especially difficult. However, these steps quickly become daunting when you consider all the files that must be managed. A full Red Hat Linux 7.3 installation provides around 3,000 executable commands and over 160,000 total files (some other Linux distributions are even larger!). Obviously, managing all these files by hand, although theoretically possible, is not technically feasible. On a smaller scale, even management of single applications is not practical. The Postfix e-mail server application, for example, consists of around 275 files scattered in a dozen or so different directories. Imagine trying to remember and manually remove all of those files (and only those files) to uninstall Postfix from your system!

All the steps needed to manage software on Unix or Linux systems are hardly unique to Unix; all operating systems have similar procedures that must be followed to make software usable on the system. For this reason, many approaches have been adopted toward software installation, uninstallation, and upgrading.

Application-level utilities

Some operating systems, such as MS-DOS, have supplied absolutely no built-in tools for software management. Installation of applications on such systems occurs in one of two ways: software is installed manually, using file-copy utilities to put all the application files in the appropriate places on the system, or software is installed using a custom-written installation application (as is usually the case for MS-DOS applications).

Once installed, software can be uninstalled in one of two ways: you can manually delete each file installed for the application (assuming you can even remember them all), or the application might come with a custom uninstallation utility that can be run to remove the application. Upgrading an already installed application on such a system uses a similar procedure. If the application comes with an installation utility capable of handling application upgrades, you can use the utility to perform the upgrade. Otherwise, the software must be manually upgraded using the procedure described previously.

Note

Current versions of Windows, such as Windows XP, though, have a central database of installed applications.

Built-in system utilities

Other operating systems have come with built-in utilities that a system administrator can use to manage the system’s software. These utilities can be run to install the software on the system; typically, they take some of the work out of manually installing software, dealing with issues such as figuring out which files need to be put where on the system. Once installed, these utilities typically track the files that have been installed. This knowledge can usually be used to uninstall those applications automatically. Since the software knows which files are associated with the application, it can be told to uninstall the application, and it can find and delete all the files that belong to that application.

These built-in utilities typically come in two different forms. One type focuses on managing the installation process, providing custom utilities that can be used to perform the otherwise manual tasks of compiling software and copying files into their final locations. The three major freely available Berkeley Unix, or BSD, operating systems, NetBSD, FreeBSD, and OpenBSD, for example, ship with a software-management system called, variously, ports (FreeBSD and OpenBSD) or packages (NetBSD).

The ports system is composed of extensions to the normal Unix software-compilation utilities that help it automate and track many of the steps of a standard source-code compilation. When using ports, you still download source code, unarchive it, configure it, compile it, and install it, but the ports software automates many of these steps. Furthermore, the ports system does limited tracking of the files it installs. Although it does not offer more advanced features (such as an interface to search all installed files to see what application supplied that file) or the ability to upgrade installed applications, it does provide the ability to uninstall applications that are installed using ports. These sorts of limitations are typical of management applications that function as the ports system does, by enhancing the compilation and installation phases of application installation. The packages system on NetBSD has similar limitations.

Other system-management utilities focus less attention on compiling an application for installation and more attention on the files that must be installed on the system after the application has been compiled.

For example, the standard System V Unix package-management software supplied with most commercial Unix systems (Sun's Solaris, for example) devotes no attention to management of software compilation at all. Instead, it tracks the individual files associated with each application in a system database.

To install software using the System V tools, you must compile the software. After compiling the software in the standard fashion, prepare a list of the files from that compilation that need to be installed on the system. Be certain to state where the files need to be installed and what permissions and ownerships they need to have once installed. Then run a series of commands that look at this list, find the files listed in it, and archive them into one file, along with a copy of this list that specifies where they should be installed and the ownerships and permissions. This single archive file can then be transferred to other machines, where a System V software-management command can be used to install it. This System V installation command (typically called pkgadd) unpacks the archive, copies the files into their final destinations based on the enclosed listing, and sets permissions and ownerships on the files as specified by the listing. Finally, this pkgadd command registers the list of freshly installed files into a system-wide database of installed files.

Such a system offers several advantages over manual software installation. Software can now be installed and uninstalled easily, and the system-wide database of installed files can be readily searched to locate installed applications and files. However, this sort of system also has severe limitations; it is far less flexible in the software-configuration stages than software such as the FreeBSD ports system, which offers great control over the software-compilation stage of software installation.

Linux Software Management Tools: Packages

Initially, Linux had neither type of software-management tool. In the early days of Linux, you installed Linux by cross-compiling it under a different operating system (Minix), then manually installing the compiled Linux programs into the appropriate locations to produce a working system. As Linux has matured, however, it has acquired software-management tools that have made software installation, removal, and upgrade significantly easier than in the early days. The exact software-management tool used on modern Linux systems varies from distribution to distribution, but both approaches to system management can be found in the tools used by various distributions.

The Gentoo Linux (www.gentoo.org) distribution, for example, uses a software-management system called Portage, which is very similar to the FreeBSD ports system. Like ports, Portage provides great control over software compilation and installation, providing a collection of scripts that automate much of the basic work of downloading and compiling software.

At the other end of the spectrum, the now-defunct deepLinux distribution used a software-management system called deep-package (still available from www2.cddc.vt.edu/linux/distributions/deeplinux/tools. deep-package was intended to be a complete reimplementation of the Solaris pkgadd utility and its helpers. Like the Solaris pkgadd software, deep-package paid no attention to half of the question of how to manage software, focusing entirely on software installation and tracking issues while entirely ignoring the initial compilation of the software.

More typically, however, Linux software-management tools use an approach somewhere between the two extremes represented by Portage and deep-package. Most Linux software-management tools provide software that manages the compilation of software, similarly to the FreeBSD ports tools. However, these software-management tools typically produce packages from the software they compile. Much like the archives produced by the System V software-management tools, packages are simply archive files that contain two things: a collection of related files, which together have a common use, and a script that provides all the metadata about those files necessary to install and manage those files.

Typically, packages represent applications. For example, a Postfix package contains the 275 files that make up Postfix and a script that specifies where on the system those 275 files need to be placed, as well as what permissions and ownership those files need. A single command can then take this Postfix package file, extract its 275 archived files, and use the script to place those files correctly on the system.

In addition, most Linux software-management tools have a database component that tracks files and applications that have been installed using the package-management software, helping the package manager do its job of easing the management of installed software.

In the case of my full Red Hat Linux 7.3 installation, this package-management software maintains a database of information regarding all 160,000 files on the system; as applications are installed on the system, this database is updated with information regarding the new application and the locations of its component files. This database is the key component, making it possible to manage the system. Since this database remembers which 275 files compose the Postfix application, it ensures that I can uninstall Postfix with a single command that accesses this database, without my having to remember the locations of all 275 files that make up the Postfix application.

A wide variety of software-management tools are available for Linux to help lessen the work involved with installing, removing, and upgrading applications installed on the system. This book focuses on one of these tools, the RPM Package Management software, or RPM.

Note

RPM was originally called Red Hat Package Manager. After adoption by other Linux distributions, the name has changed to simply the RPM Package Manager. The RPM initials remain the same.

As the original name implies, RPM was developed by Red Hat, Inc., the major Linux distributor in the United States. Even though the original name seems to point to a Red Hat-only solution, most Linux distributions use the RPM software. The RPM software provides a foundation needed by Linux system administrators throughout the world. You can even use RPM on other operating systems, both Linux and non-Linux, as covered in Chapters 19 and 20, respectively.

The RPM system provides all of the features needed to manage applications, including a database of installed packages with their version numbers, the ability to install, remove, and update packages, and the ability to recompile an application from a source code RPM package.

The remaining chapters in Part I go into depth on what you can do with RPM packages and the commands you need to work with the RPM system:

*	Chapter 2 provides an overview of the RPM system, exploring what it was designed for and where it has weaknesses.

*	Chapter 3 discusses the technical details of how the RPM system works, where the database of packages gets stored, and what commands should be available for working with RPM packages.

*	Chapter 4 continues the discussion by covering the three major tasks you need to perform with RPM packages: installing software, removing software, and upgrading software you have already installed.

*	Chapter 5 covers the RPM database, how it works, where it resides, and how you can use it to better manage your system.

*	Chapter 6 delves into package dependencies, a very important concept. Most major applications depend on a number of other packages. Sometimes these dependencies get very complex, with one package depending on particular versions of other packages. With thousands of packages on your system, this can lead to a big mess. Chapter 6 helps you sort through the issues.

*	Chapter 7 covers the important issue of transactions, so that you can ensure your system gets updated in an orderly manner and so that you can roll back changes if something does not work out.

*	Chapter 8 introduces a host of tools that can help you find RPM packages as well as manage the packages on your system. This includes graphical interfaces on top of the RPM system and special Internet search sites devoted just to RPM packages.

Later chapters cover creating RPM packages, programming with RPM, and extending the functionality provided by the base RPM system.

Summary

Modern operating systems have large complex sets of applications, resulting in thousands of files to keep track of for upgrades, installation, and removal of packages. All this complexity has lead Linux vendors to develop a variety of package-management tools.

This chapter briefly introduced the RPM Package Manager, or RPM for short. The next chapter provides an overview of the RPM system, showing how all the parts fit together.

Chapter 01

Chris Ricker

2003-01-14T13:02:00

Eric Foster-Johnson