Chapter 5. Red Hat and Debian Package Managers

This chapter describes the two major Linux packaging systems: the Red Hat Package Manager (RPM) and the Debian GNU/Linux Package Manager.

When you install applications on your Linux system, most often you'll find a binary or a source package containing the application you want, instead of (or in addition to) a .tar.gz file. A package is a file containing the files necessary to install an application. However, while the package contains the files you need for installation, the application might require the presence of other files or packages that are not included, such as particular libraries (and even specific versions of the libraries), to actually be able to run. Such requirements are known as dependencies.

Package management systems offer many benefits. As a user, you may want to query the package database to find out what packages are installed on the system and their versions. As a system administrator, you need tools to install and manage the packages on your system. And if you are a developer, you need to know how to build a package for distribution.

Among other things, package managers do the following:

• Provide tools for installing, updating, removing, and managing the software on your system.

• Allow you to install new or upgraded software directly across a network.

• Tell you what software package a particular file belongs to or what files a package contains.

• Maintain a database of packages on the system and their state, so you can find out what packages or versions are installed on your system.

• Provide dependency checking, so you don't mess up your system with incompatible software.

• Provide PGP, MD5, or other signature verification tools.

• Provide tools for building packages.

Any user can list or query packages. However, installing, upgrading, or removing packages generally requires superuser privileges. This is because the packages normally are installed in systemwide directories that are writable only by root. Sometimes you can specify an alternate directory to install a package into your home directory or into a project directory where you have write permission.

Both RPM and the Debian Package Manager back up old files before installing an updated package. Not only does this let you go back if there is a problem, but also ensures that you don't lose your changes (to configuration files, for example).