What legal issues come up if I use GPL-incompatible libraries with GPL software?
Both versions of the GPL have an exception to their copyleft, commonly called the system library exception. If the GPL-incompatible libraries you want to use meet the criteria for a system library, then you don’t have to do anything special to use them; the requirement to distribute source code for the whole program does not include those libraries, even if you distribute a linked executable containing them. The criteria for what counts as a “system library” vary between different versions of the GPL. GPLv3 explicitly defines “System Libraries” in section 1, to exclude it from the definition of “Corresponding Source.” GPLv2 says the following, near the end of section 3: However, as a special exception, the source code distributed need not include anything that is normally distributed (in either source or binary form) with the major components (compiler, kernel, and so on) of the operating system on which the executable runs, unless that component itself accompanies the executable.
Both versions of the GPL have an exception to their copyleft, commonly called the system library exception. If the GPL-incompatible libraries you want to use meet the criteria for a system library, then you don’t have to do anything special to use them; the requirement to distribute source code for the whole program does not include those libraries, even if you distribute a linked executable containing them. The criteria for what counts as a “system library” vary between different versions of the GPL. GPLv3 explicitly defines “System Libraries” in section 1, to exclude it from the definition of “Corresponding Source.” GPLv2 says the following, near the end of section 3: However, as a special exception, the source code distributed need not include anything that is normally distributed (in either source or binary form) with the major components (compiler, kernel, and so on) of the operating system on which the executable runs, unless that component itself accompanies the executable. If y
GPLv2 has an exception allowing GPLed works to link against system libraries, regardless of their license, in section 1. GPLv3 has slightly expanded this exception, to include works like language standard libraries, in section 3. If the libraries you’re using fall under the appropriate exception, then you don’t have to do anything special to use them; the requirement to distribute source code for the whole program does not include those libraries, even if you distribute a linked executable containing them. Thus, if the libraries you need come with major parts of a proprietary operating system, the GPL says people can link your program with them without any conditions. If you want your program to link against a library not covered by that exception, you need to add your own exception, wholly outside of the GPL. This copyright notice and license notice give permission to link with the program FOO: Copyright (C) yyyy
If the libraries that you link with fall within the following exception in the GPL: However, as a special exception, the source code distributed need not include anything that is normally distributed (in either source or binary form) with the major components (compiler, kernel, and so on) of the operating system on which the executable runs, unless that component itself accompanies the executable. then you don’t have to do anything special to use them; the requirement to distribute source code for the whole program does not include those libraries, even if you distribute a linked executable containing them. Thus, if the libraries you need come with major parts of a proprietary operating system, the GPL says people can link your program with them without any conditions. If you want your program to link against a library not covered by that exception, you need to add your own exception, wholly outside of the GPL. This copyright notice and license notice give permission to link with the p
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