Friday, April 26, 2013

GPL and LGPL licenses

Most of the components making up a Linux system are distributed under two type of licenses :

  •  GPL : mainly used for applications (gcc compiler, gdb debugger)
  •  LGPL : mainly used for libraries (C library, GTK widget toolkit, ...)

Other licenses exist (BSD, Mozilla, ...) but are less used.

GPL restrictions
(summarized) :

  • one can make several copies of the program as long as the licence and copyright remain intact
  • a program distributed under this licence comes with no warranty whatsoever unless it is brought by the distributor
  • you can charge for the act of copying and for warranty protection
  • if you distribute copies of the binary, you must accompany them with the original source code
  • if you're modifying the source code of a GPL binary, the resulting program will be subject to the GPL license as well with no additional restriction permitted

If you're planning to link your software against a GPL-licensed library (statically or dynamically), you're falling under the GPL too. It is the main difference with LGPL which allows you to use unmodified parts of a program without license restriction. Thus, you can link against an LGPL library with no fear of being forced to distribute your binary under the same license. However, you are not free to distribute a modified LGPL library under any other license than LGPL.

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