Software License
Copyleft License
A copyleft license is a specific type of software license that allows software to be freely used, modified, and shared. However, any derivative works must also be distributed under the same license terms. This ensures that the freedoms associated with the software are preserved in all subsequent adaptations. This article delves into the intricacies of copyleft and its impact on software development and distribution.
Origins and Development
The concept of copyleft was pioneered by Richard Stallman as part of the GNU Project, which aimed to create a completely free and open-source operating system. The first copyleft license, the GNU General Public License, or GPL, was written as a means to safeguard the freedom to share and change free software, ensuring it remains free for all its users.
The GPL is significant as it was the first software license to incorporate copyleft principles. Under the GPL, any software derived from GPL-licensed code must also be licensed under the GPL, thus propagating the freedom to use, study, modify, and distribute the software.
Types of Copyleft Licenses
Several variations of copyleft licenses exist, each with different scopes and compatibility considerations:
- GNU General Public License: The most prevalent copyleft license, ensuring that any modified versions of GPL-licensed code are also distributed under the GPL terms.
- GNU Lesser General Public License: Designed for software libraries, this license applies copyleft principles more leniently to encourage linking with non-GPL software.
- GNU Affero General Public License: Extends the GPL's reach to cover software delivered over a network, ensuring users of networked applications can receive the source code.
- Free Art License: Aimed at artistic works, this copyleft license allows for free copying, distribution, and transformation of creative content.
Copyleft vs. Permissive Licenses
Copyleft licenses differ substantially from permissive licenses, such as the MIT License or BSD licenses, which impose minimal restrictions on the distribution of modified software. Permissive licenses allow proprietary derivatives, whereas copyleft licenses ensure that all derivatives remain free.
License Compatibility
A critical aspect of copyleft licenses is their compatibility with other licenses. Copyleft licenses often allow relicensing under certain other copyleft licenses, but this can present challenges. For instance, integrating GPL-licensed code into a project with a non-copyleft license requires careful consideration of license terms to avoid conflicts.
Impact on Software Development
The copyleft model has had a profound impact on the free and open-source software (FOSS) movement. By enforcing the freedom to share and modify software, copyleft licenses promote collaborative development and innovation, leading to the creation of robust, community-driven software projects.
Copyleft encourages a culture of sharing and continuous improvement, which has been instrumental in the widespread adoption and success of many open-source projects, such as the Linux operating system and the Apache HTTP Server.
Related Topics
Software License
A software license is a legal instrument that governs the use or redistribution of software. It serves as an agreement between the author and the user, detailing how software can be used, modified, or distributed. Software licenses have been a fundamental component of the software industry since the 1970s, largely due to the recognition of software copyright.
Types of Software Licenses
Software licenses can broadly be categorized into several types, each with different permissions and restrictions.
Free-Software License
A free-software license provides users extensive rights to modify and redistribute software. It aligns with the philosophy of free and open-source software. These licenses are often seen as a social contract empowering users with control over their computing.
Open-Source License
Open-source licenses ensure that software can be freely used, modified, and shared. They facilitate the development of open-source projects and align closely with free-software licenses.
Permissive Software License
Permissive software licenses, such as the MIT License and BSD licenses, impose minimal restrictions on the use and distribution of software. They are often preferred for their simplicity and flexibility.
Copyleft License
Copyleft licenses, like the GNU General Public License, require that derivative works of the software also be open and free, ensuring that improvements to the software remain accessible to the public.
Proprietary Software License
Proprietary software licenses restrict the use, modification, and distribution of software. Users typically obtain a license to use the software under terms set by the owner, often without access to the source code.
Volume and Site Licensing
Volume licensing and site licenses are used to authorize software on a large number of computers or across an entire organization, offering cost efficiency and ease of management.
End-User License Agreement
An End-User License Agreement (EULA) is a legal contract between the software supplier and the user, detailing the terms under which the software may be used.