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Before diving into the world of Linux software package management, this chapter goes through a few of the basics of how Linux manages application software. Each of the major Linux distributions utilizes some form of a package management system to control installing software applications and libraries. A package management system uses a database that keeps track of the following:

 What software packages are installed on the Linux system

 What files have been installed for each package

 Versions of each of the software packages installed

Software packages are stored on servers, called repositories, and are accessed across the Internet via package management system utilities running on your local Linux system. You can use these utilities to search for new software packages or even updates to software packages already installed on the system.

A software package will often have dependencies, or other packages that must be installed first for the software to run properly. The package management system utilities will detect these dependencies and offer to install any additionally needed software packages before installing the desired package.

The downside to a package management system is that there isn't a single standard utility. Not all software package management systems work in all Linux distributions.

The package management system utilities and their associated commands are vastly different between the various Linux distributions. The two primary package management system base utilities commonly used in the Linux world are dpkg and rpm.

Debian‐based distributions such as Ubuntu use, at the base of their package management system utilities, the dpkg command. This command interacts directly with the package management system on the Linux system and is used for installing, managing, and removing software packages.

The Red Hat–based distributions, such as CentOS, use the rpm command at the base of their package management system. Similar to the dpkg command, the rpm command can list installed packages, install new packages, and remove existing software.

Note that these two commands are the core of their respective package management system, not the entire package management system itself. Many Linux distributions that use the dpkg or rpm methods have built additional specialty package management system utilities upon these base commands to make your life much easier. The following sections walk through the package management systems you'll find in Debian‐based systems, such as Ubuntu. Chapter 5, “Installing and Maintaining Software in Red Hat,” covers using the rpm package management system.