The Ubuntu software repository contains thousands of software packages organized into five components on the basis of the level of support we can offer them and whether or not they comply with our Free Software Philosophy. The components are called main, restricted, universe, multiverse, and commercial.
The Ubuntu software repository is divided into four components—main, restricted, universe, and multiverse—on the basis of our ability to support that software and whether or not it meets the goals laid out in our Free Software Philosophy.
The standard Ubuntu installation is a subset of software available from the main and restricted components. You can install additional software using installation software such as Synaptic Package Manager or Aptitude. Other components are added by editing the /etc/apt/sources.list file. See man sources.list for more information on editing the sources.list file.
The main distribution component contains applications that are free software, can freely be redistributed, and are fully supported by the Ubuntu team. This includes the most popular and most reliable open source applications available, much of which is installed by default when you install Ubuntu.
Software in main includes a hand-selected list of applications that the Ubuntu developers, community, and users feel are important and that the Ubuntu security and distribution teams are willing to support. When you install software from the main component, you are assured that the software will come with security updates and technical support.
We believe that the software in main includes everything most people will need for a fully functional desktop or Internet server running only open source software.
The licenses for software applications in main must be free, but main also may contain binary firmware and selected fonts that cannot be modified without permission from their authors. In all cases, redistribution is unencumbered.
The restricted component is reserved for software that is very commonly used and which is supported by the Ubuntu team even though it is not available under a completely free license. Please note that it may not be possible to provide complete support for this software since we are unable to fix the software ourselves but can only forward problem reports to the actual authors.
Some software from restricted will be installed on Ubuntu CDs but is clearly separated to ensure that it is easy to remove. We include this software because it is essential in order for Ubuntu to run on certain machines. Typical examples are the binary drivers that some video card vendors publish, which are the only way for Ubuntu to run on those machines. By default, we will only use open source software unless there is simply no other way to install Ubuntu. The Ubuntu team works with such vendors to accelerate the open sourcing of their software to ensure that as much software as possible is available under a free license.
The universe component is a snapshot of the free, open source, and Linux world. In universe you can find almost every piece of open source software and software available under a variety of less open licenses, all built automatically from a variety of public sources. All of this software is compiled against the libraries and using the tools that form part of main, so it should install and work well with the software in main, but it comes with no guarantee of security fixes and support. The universe component includes thousands of pieces of software. Through universe, users are able to have the diversity and flexibility offered by the vast open source world on top of a stable Ubuntu core.
Popular or well-supported pieces of software will move from universe into main if they are backed by maintainers willing to meet the standards set for main by the Ubuntu team.
The multiverse component contains software that is not free, which means the licensing requirements of this software do not meet the Ubuntu "Main" Component License Policy.
The onus is on you to verify your rights to use this software and comply with the licensing terms of the copyright holder.
This software is not supported and usually cannot be fixed or updated. Use it at your own risk.