Basic introduction Chinese name: General Public License mbth: GNU General Public License Abbreviation: GNU GPL Writing: Richard Storman Nature: Version, concept and version of free software license GPLv 1 GPLv 1 is the original version, released in June of 5438+0989 and June of 5438+0. Its purpose is to prevent those behaviors that hinder free software. There are two main behaviors that hinder software open source (one is that software publishers only release executable binary code without releasing source code, and the other is that GPLv 1 stipulates that if executable binary code is released, readable source code must be released at the same time, and no restrictive clauses can be added when releasing any software based on GPL license. The biggest change of GPLv2 in GPLv2 is the addition of "freedom or death". This clause stipulates that if the software originated from GPL can only be distributed in the form of binary code, then he has no right to distribute the software at all. GPLv3 was released on June 29th, 2007. There are four most important amendments: solving the software patent problem; Compatibility with other licenses; Definition of source code division and combination; Solve the problem of digital rights management (DRM). A key concept in GPL is Copyleft. GPL stipulates that the grant of redistribution right requires the licensee to disclose the source code and all modifications of the software, and copies and modified versions must be approved by GPL. These requirements are Copyleft, which is based on the legal copyright of the work. Due to copyright reasons, generally speaking, unless there is a Copyleft clause, the licensee has no right to modify and redistribute the work (except for fair use). Copyfleft uses copyright law to achieve the opposite goal: Copyfleft gives people inalienable rights instead of many restrictions stipulated by copyright law. This is why GPL is called "the hacked copyright law". Copyleft only takes effect when the program is redistributed. Modifications to the software shall not disclose or open the source code, as long as they are not distributed. Note that copyleft is only valid for software, but not for software output (unless the output is the software itself).