Portage is a package management system originally created for and used by Gentoo Linux and also by ChromeOS, Calculate, Sabayon, and Funtoo Linux among others. Portage is based on the concept of ports collections. Gentoo is sometimes referred to as a meta-distribution due to the extreme flexibility of Portage, which makes it operating-system-independent. The Gentoo/Alt project was concerned with using Portage to manage other operating systems, such as BSDs, macOS and Solaris. The most notable of these implementations is the Gentoo/FreeBSD project.
There is an ongoing effort called the Package Manager Specification project (PMS), which aims to standardise and document the behaviour of Portage, allowing the ebuild tree and Gentoo system packages to be used with alternative package managers such as Paludis and pkgcore. Its goal is to specify the exact set of features and behaviour of package managers and ebuilds, serving as an authoritative reference for Portage.
Overview
Accessing Portage
Portage is similar to the BSD-style package management known as ports, and was originally designed with FreeBSD's ports in mind. Portage is written in the Python programming language, and is the main utility that defines Gentoo. Although the system itself is known as Portage, it consists of two main parts, the ebuild system and emerge. The ebuild system takes care of the actual work of building and installing packages, while emerge provides an interface to ebuild: managing an ebuild repository, resolving dependencies and similar issues. (These two therefore have roughly the same relation as rpm has with yum, or dpkg has with APT.)
A GTK+-based GUI, Porthole, is available for working with Portage. There is also the Himerge GUI, which stands for "Haskell Interface for eMerge".
Functions provided
Portage is characterized by its main function: compiling from source code the packages the user wishes to install. In doing so it allows customization of compiler and target-application options to fit the system's specifications and the user's own wishes. Functionalities related to system management include: allowing parallel package-version installation, tracking cross-package dependencies, managing a database of installed packages, providing a local ebuild repository, and synchronizing of the local Portage tree with remote repositories. Functionalities related to individual package installation include: specifying compilation settings for the target machine and choosing package components.
Portage distinguishes between three levels of stability in ebuilds: stable (e.g., the software works as intended with no known security issues at time of release), keyword masked (mainly for packages that have not been sufficiently tested on the target system architecture to be considered stable) and hard masked (broken or very insecure) packages.
Features
Emerge
The emerge command-line tool is the heart of Portage. The command is customizable with many options and modifiers. The emerge tool is the most important utility for accessing the features of Portage from the command line.
The program calculates and manages dependencies, executes ebuilds and maintains the local Portage tree and database of installed packages. The compilation settings used by ebuilds can be changed through the CFLAGS environment variable, based on the specifications of the individual computer and on the user's desire for optimization. The emerge utility executes ebuilds in a sandbox environment. This way the system is protected from software executed by the ebuild and resulting binaries are only merged after a successful build and sandboxed install.
What emerge installs as dependencies is affected by the USE flag-settings. They decide which optional features will be included when installing or upgrading an application. The emerge command can also be used to download and install precompiled binary files.
USE flags
The Portage system offers the use of "USE flags", which allows users to indicate which software features they would like to include (and exclude) while building packages. For example, there is a USE flag to include DVD support, where available, in packages compiled with the flag enabled. The USE flags affect which dependencies are required, generally affecting which optional features will be built into a given program when it is compiled. For example, in packages which use a configure script, the USE flag feature would translate to ./configure --with-feature.