The RPM Package Manager (RPM) is an open packaging system, available for anyone to use, which runs on Red Hat Enterprise Linux as well as other Linux and UNIX systems. Red Hat, Inc. encourages other vendors to use RPM for their own products. RPM is distributable under the terms of the GPL.
For the end user, RPM makes system updates easy. Installing, uninstalling, and upgrading RPM packages can be accomplished with short commands. RPM maintains a database of installed packages and their files, so you can invoke powerful queries and verifications on your system. If you prefer a graphical interface, you can use the Package Management Tool to perform many RPM commands. Refer to Chapter 16 Package Management Tool for details.
During upgrades, RPM handles configuration files carefully, so that you never lose your customizations — something that you cannot accomplish with regular .tar.gz files.
For the developer, RPM allows you to take software source code and package it into source and binary packages for end users. This process is quite simple and is driven from a single file and optional patches that you create. This clear delineation between pristine sources and your patches along with build instructions eases the maintenance of the package as new versions of the software are released.
Because RPM makes changes to your system, you must be root to install, remove, or upgrade an RPM package.
To understand how to use RPM, it can be helpful to understand RPM's design goals:
Using RPM, you can upgrade individual components of your system without completely reinstalling. When you get a new release of an operating system based on RPM (such as Red Hat Enterprise Linux), you do not need to reinstall on your machine (as you do with operating systems based on other packaging systems). RPM allows intelligent, fully-automated, in-place upgrades of your system. Configuration files in packages are preserved across upgrades, so you do not lose your customizations. There are no special upgrade files needed to upgrade a package because the same RPM file is used to install and upgrade the package on your system.
RPM is designed to provide powerful querying options. You can do searches through your entire database for packages or just for certain files. You can also easily find out what package a file belongs to and from where the package came. The files an RPM package contains are in a compressed archive, with a custom binary header containing useful information about the package and its contents, allowing you to query individual packages quickly and easily.
Another powerful feature is the ability to verify packages. If you are worried that you deleted an important file for some package, verify the package. You are notified of any anomalies. At that point, you can reinstall the package if necessary. Any configuration files that you modified are preserved during reinstallation.
A crucial design goal was to allow the use of "pristine" software sources, as distributed by the original authors of the software. With RPM, you have the pristine sources along with any patches that were used, plus complete build instructions. This is an important advantage for several reasons. For instance, if a new version of a program comes out, you do not necessarily have to start from scratch to get it to compile. You can look at the patch to see what you might need to do. All the compiled-in defaults, and all of the changes that were made to get the software to build properly, are easily visible using this technique.
The goal of keeping sources pristine may only seem important for developers, but it results in higher quality software for end users, too.