GNU通用公共许可证详解

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"GNU General Public License (GPL) 是一个广泛使用的自由软件许可证，旨在保护用户对软件的自由使用、研究、分享和修改的权利。" GNU General Public License（GPL）是自由软件基金会（Free Software Foundation，FSF）由理查德·斯托曼（Richard Stallman）为GNU项目创建的一个关键法律工具。它是一种 Copyleft 许可证，意味着任何基于GPL授权软件的衍生作品也必须使用相同的GPL许可证发布，以此确保软件的自由性持续下去。 GPL有多个版本，其中最知名的两个是GPLv2和GPLv3。GPLv2于1991年首次发布，旨在解决当时软件版权法的一些问题，保障用户可以自由地访问、修改和重新分发软件代码。而GPLv3在2007年6月29日发布，更新了对数字版权管理（DRM）、专利许可和国际法律适用性的条款，以更好地适应互联网时代的需求。 GPL的关键条款包括： 1. **源代码提供**：如果软件被分发，那么必须提供源代码或提供获取源代码的途径。 2. **修改权**：用户有权修改软件，并且可以保留修改后的软件作为自己的作品。 3. **再分发权**：用户可以自由地将软件（包括修改版）分发给他人，但必须包含原始和修改后的源代码。 4. **Copyleft**：当用户将修改后的软件再次分发时，必须使用相同的GPL许可证，这确保了下游用户也能享受同样的自由权利。 5. **不兼容的链接**：通常情况下，GPL软件不能与其他使用不同许可证（尤其是非Copyleft许可证）的软件链接，除非这些软件也符合GPLv3的特定条件。 GPL与其它开源许可证的主要区别在于其Copyleft特性，这使得它成为保护开源精神的强大力量。然而，这种严格的条件也导致了一些争议，特别是对于商业软件开发者来说，他们可能更倾向于选择允许更宽松使用和集成的许可证，如MIT、Apache或BSD等。 GNU GPL是自由软件运动的基石，它不仅定义了软件的自由使用标准，还推动了开放源代码软件的发展和创新。许多著名的项目，如Linux内核、GNU工具链和WordPress，都采用GPL许可证，从而确保它们始终对所有人开放。

2014年3月26日 GNU General Public License - Wikipedia, the free encyclopedia
http://en.wikipedia.org/wiki/GPLv2#Version_2 5/25
The third draft was released on 28 March 2007.
[29]
 This draft included language
intended to prevent patent-related agreements like the controversial Microsoft-Novell
patent agreement and restricts the anti-tivoization clauses to a legal definition of a
"User" or "consumer product". It also explicitly removed the section on "Geographical
Limitations", whose probable removal had been announced at the launch of the public
consultation.
The fourth discussion draft,
[30]
 which was the last, was released on 31 May 2007. It
introduced Apache License compatibility, clarified the role of outside contractors,
and made an exception to avoid the perceived problems of a Microsoft–Novell style
agreement, saying in Section 11 paragraph 6 that
You may not convey a covered work if you are a party to an arrangement with
a third party that is in the business of distributing software, under which
you make payment to the third party based on the extent of your activity of
conveying the work, and under which the third party grants, to any of the
parties who would receive the covered work from you, a discriminatory patent
license [...]
This aims to make future such deals ineffective. The license is also meant to cause
Microsoft to extend the patent licenses it grants to Novell customers for the use of
GPLv3 software to all users of that GPLv3 software; this is possible only if Microsoft
is legally a "conveyor" of the GPLv3 software.
[31][32]
Also, early drafts of GPLv3 allowed licensors to add an Affero-like requirement which
would have plugged the ASP loophole in the GPL.
[33][34]
 As there were concerns
expressed about the administrative costs of checking code for this additional
requirement, it was decided to keep the GPL and the Affero license separated.
[35]
Others, notably some high-profile developers of the Linux kernel, commented to the
mass media and made public statements about their objections to parts of discussion
drafts 1 and 2.
[36]
GPLv3 improves compatibility with several open source software licenses such as Apache
License, version 2.0, and the GNU Affero General Public License which GPLv2 could not
be combined with,
[37]
 but GPLv3 software can only be combined with GPLv2 software if
the GPLv2 version has the optional "or later" clause of the GPL. "GPLv2 or any later
version" is considered by FSF as the most common form of licensing GPLv2 software
[38]
while for example Toybox developer Rob Landley described it as a lifeboat clause.
[39]
Software projects which are licensed with the optional "or later" clause include the
GNU Project, while a prominent example without the clause is the Linux kernel.
[12]
The final version of the license text was published on 29 June 2007.
[40]
Adoption