Reference
https://www.cnblogs.com/findumars/p/3556883.html
GPL
We are very familiar with Linux is to use the GPL. The GPL and BSD, Apache Licence and so encourage code reuse license very different. The starting point of the GPL open source code / free use and reference / modification / derivative code open source / free, but not allowed to modify the code and derived as a closed-source commercial software distribution and sales. This is why we can use a variety of free linux, including a variety of by individuals, organizations, and commercial software free software developed by commercial companies on the linux and linux.
The main content of the GPL is to simply use ( "use" refers to the class library reference, the revised code or derivative of this code) GPL agreement in a software product, the software product must also be GPL license must also be both open source and free . This is called "contagious." The GPL products as a separate product without any problems, you can also enjoy free advantage.
Due to the stringent requirements of the use of the GPL GPL library of software products must use the GPL, GPL agreement for the use of open source, commercial software or code division confidentiality requirement is not suitable for integration / adoption as the basis for the development of libraries and secondary .
Other details are similar when re-released as GPL requires accompanying agreements and BSD / Apache and so on.
LGPL
LGPL is a GPL is designed for use primarily open source libraries agreement. And the use of any software requirements GPL / modify / GPL-derived library must use different protocols GPL. LGPL allow commercial software library reference (link) mode without using the open source code library LGPL commercial software. This makes use of the LGPL open source code can be used as a reference library and publish and sell commercial software.
However, if the code changes the LGPL or derivatized, all the modified code, the code involves additional code modifications and derived portions must use the LGPL. Thus the LGPL open source code is very suitable as a third-party commercial software libraries are referenced, but not for those who want to the LGPL code base, and derived by modifying the way to do secondary development of business software used.
GPL / LGPL are the original author of protecting intellectual property rights, prevent people from copying and use of open-source development of similar products.
Essence
As a GPL library, on your entire software code must be open source.
LGPL can be used as a library, not open source, but once changed the library, you need to modify the open source library.
