What is a package manager?

What is a package manager?
	Introduction

A package manager keeps track of what software is installed on your computer, and allows you to easily install new software, upgrade software to newer versions, or remove software that you previously installed. As the name suggests, package managers deal with packages: collections of files that are bundled together and can be installed and removed as a group.

Often, a package is just a particular program. For instance, the instant messaging client gaim is contained in the Debian package of the same name. On the other hand, it is common for programs to consist of several interrelated packages. For instance, the gimp image editor consists not only of the gimp package, but also of the gimp-data package; in addition, several optional add-on packages (containing esoteric data, documentation, and so on) are also available. It is also possible for several small, related programs to be contained in a single package: for instance, the fileutils package contains several common Unix commands, such as ls, cp, etc.

Some packages require other packages in order to function. In Debian, packages can depend upon, recommend, suggest, break, or conflict with other packages.

If a package A depends upon another package B, then B is required for A to operate properly. For instance, the gimp package depends upon the gimp-data package in order to ensure that the GIMP graphics editor can access its critical data files.
If a package A recommends another package B, then B provides important additional functionality to A that will be desired in most circumstances. For instance, the mozilla-browser package recommends the mozilla-psm package, which adds support for secure data transfers to the Mozilla Web browser. While mozilla-psm is not strictly required for Mozilla to function, most users will want Mozilla to support the secure transmission of confidential data (such as credit card numbers).
If a package A suggests another package B, then package B provides functionality that may enhance A, but is not needed in most cases. For instance, the kmail package suggests the gnupg package, which contains encryption software that can be used by KMail.
If a package A conflicts with another package B, then the two packages cannot be installed at the same time. For instance, fb-music-hi conflicts with fb-music-low because they provide alternate sets of music for the game Frozen Bubble.

The job of a package manager is to present an interface which assists the user in managing the collection of packages installed on his or her system. aptitude provides such an interface by building on the apt package management system.


What is this aptitude thing, anyway?		What is the `apt` system?