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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 (http://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. 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 a full Fedora 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.

Change of Name

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, many 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 Chapter 18, Using RPM on Non-Red Hat Linuxes and Chapter 19, RPM on Other Operating Systems, 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:
  1. Chapter 1, Introduction to RPM provides an overview of the RPM system, exploring what it was designed for and where it has weaknesses.
  2. Chapter 2, RPM Overview 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.
  3. Chapter 3, Using RPM 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.
  4. Chapter 4, Using the RPM Database covers the RPM database, how it works, where it resides, and how you can use it to better manage your system.
  5. Chapter 5, Package Dependencies 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. This chapter helps you to sort through the issues.
  6. Chapter 6, Transactions 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.
  7. Chapter 7, RPM Management Software 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.