Several package managers are available for Linux to track and manipulate the applications installed on the system. The most widely used of these Linux package managers is the RPM Package Manager (formerly the Red Hat Package Manager), or RPM for short, the subject of this book
Although RPM was initially developed for Red Hat Linux, a combination of technical features and good timing has resulted in RPM’s becoming the de facto standard for packaging software on most Linux distributions. The fact that Red Hat released the source code to the RPM software under an open-source license also helped its adoption.
Strictly speaking, Linux refers to a single piece of software, the Unix-like kernel that Linus Torvalds and cohorts have scattered all over the Internet and have been developing since 1991. This Linux kernel is a marvelous piece of software, currently comprising over 3.7 million lines of freely-licensed source code and accompanying documentation. Together, these factors provide a fast, full-featured, stable operating system kernel for use on more than 30 different processor architectures, ranging from embedded systems such as watches and PDAs, to desktop and server systems, all the way up to mainframes and supercomputing clusters.
1.1. The Need for Linux Package Management Systems
Although Linux is an excellent core component of an operating system suitable for a wide variety of real-world applications, this Linux kernel by itself is not sufficient for accomplishing most tasks. The technical definition of exactly what constitutes an operating system is a matter of debate.
Despite this controversy, it is clear that most users of Linux require both the Linux kernel and a large suite of accompanying software (a shared C library; traditional Unix utilities such as grep, awk, and sed; an editor, such as vi; a shell, such as the Bourne-Again bash shell; and so forth) to complete the various tasks for which they typically employ Linux.
Users expect Linux to include server software such as the Apache Web server, desktop software such as the OpenOffice.org office productivity suite, and a host of other packages. In fact, most Linux users don’t make the distinction between the kernel (technically the only part that is Linux) and all the extra packages (technically “everything else”) that comes with a Linux distribution. Most users simply refer to the whole thing as “Linux.”
Some Linux distributions include thousands of packages on six or more CD-ROMs. This situation alone cries out for effective package-management software. And this doesn’t include the extra packages that don’t come with Linux distributions but which organizations need to create an effective working environment.
Furthermore, the Linux kernel and these various software applications are typically made available by their developers in source code formats only, and they can be installed manually only after compiling them from source code.
Most people do not have the technical skills necessary to cross-compile an entire operating system. Even if they do, they usually do not want to devote the time and effort required to bootstrap and compile an operating system just to be able to run Linux.
Fortunately, the early Linux programmers quickly realized the impracticality of source-code only releases early in Linux's development and created what they called distributions—collections of precompiled binaries of the Linux kernel and other necessary software that users often wanted. Rather than installing Minix, compiling the Linux kernel and other required software applications under Minix, and installing those compiled binaries of the Linux kernel and essential Linux applications, users could just install these distributions, immediately having a functional Linux environment in which to work.
Early distributions, such as MCC and SLS, initially represented little more than archived snapshots of their developer's hard drive. They offered the user performing the installation little or no control over what applications were put on the system. Whatever the distribution developer had on his hard drive was what the distribution installer got on her hard drive. Even this was much better than rolling your own distribution by hand. SLS, for example, stood for Soft Landing System, and was designed to make the experience of installing Linux easier, hence providing a “soft landing.” MCC Interim Linux, from the Manchester Computing Centre, was the first distribution to sport a combined boot/root disk, another attempt to make life easier for those adopting Linux.
Distribution developers quickly realized, however, that more flexibility was needed and began looking for ways to provide choices both during and after installation. The Slackware distribution, for example, divided applications into several functional categories. All users installed the base distribution; users could then selectively install only the additional supplemental categories they needed. If networking support was desired, for example, the networking bundle could be installed. Similarly, if a graphical user interface was desired, the X bundle could be installed, making the X Window System available. This concept offered rudimentary control over what was installed but only at a very coarse level. Installing the X bundle put several applications (multiple X terminal emulators, several different window managers, and so forth) on the system, and all users who installed the bundle got all of those applications whether they wanted them all or not.
The next logical step in distribution evolution was the development of more advanced tools to control what was installed. Several distributions independently developed the notion of application-level installation management. The developers of these distributions realized that Slackware and similar distributions were heading in the right direction, but simply had not made software management granular enough. Slackware allowed installation and uninstallation (after a fashion) of bundles of related applications, but what was really needed was installation and uninstallation on an application-by-application basis.
In late 1993, Rik Faith, Doug Hoffman, and Kevin Martin began releasing the first public betas of the BOGUS Linux distribution. BOGUS was notable for the package management system (pms) software that was used with it for installation and uninstallation of all software on an application-by-application basis. Shortly thereafter, in the summer of 1994, the first public betas of Red Hat Commercial Linux were released. Red Hat initially used Red Hat Software Program Packages (RPP) as the basis of its Linux distribution. Like pms, RPP was a system-management tool that allowed for easy installation and uninstallation of applications. In late 1993, Ian Murdock founded the Debian Gnu/Linux distribution. He began seriously developing its dpkg application-management software by the summer of 1994. Like pms and RPP, dpkg made it possible to manage each application on the system.
