Reference Guide
91
Licensing
To protect your rights, we need to make restrictions that forbid anyone to deny you these rights or to
ask you to surrender the rights. These restrictions translate to certain responsibilities for you if you
distribute copies of the library, or if you modify it.
For example, if you distribute copies of the library, whether gratis or for a fee, you must give the
recipients all the rights that we gave you. You must make sure that they, too, receive or can get the
source code. If you link a program with the library, you must provide complete object files to the
recipients so that they can relink them with the library, after making changes to the library and
recompiling it. And you must show them these terms so they know their rights.
Our method of protecting your rights has two steps: (1) copyright the library, and (2) offer you this
license which gives you legal permission to copy, distribute and/or modify the library.
Also, for each distributor's protection, we want to make certain that everyone understands that there is
no warranty for this free library. If the library is modified by someone else and passed on, we want its
recipients to know that what they have is not the original version, so that any problems introduced by
others will not reflect on the original authors' reputations.
Finally, any free program is threatened constantly by software patents. We wish to avoid the danger
that companies distributing free software will individually obtain patent licenses, thus in effect
transforming the program into proprietary software. To prevent this, we have made it clear that any
patent must be licensed for everyone's free use or not licensed at all.
Most GNU software, including some libraries, is covered by the ordinary GNU General Public License,
which was designed for utility programs. This license, the GNU Library General Public License, applies
to certain designated libraries. This license is quite different from the ordinary one; be sure to read it in
full, and don't assume that anything in it is the same as in the ordinary license.
The reason we have a separate public license for some libraries is that they blur the distinction we
usually make between modifying or adding to a program and simply using it. Linking a program with a
library, without changing the library, is in some sense simply using the library, and is analogous to
running a utility program or application program. However, in a textual and legal sense, the linked
executable is a combined work, a derivative of the original library, and the ordinary General Public
License treats it as such.
Because of this blurred distinction, using the ordinary General Public License for libraries did not
effectively promote software sharing, because most developers did not use the libraries. We
concluded that weaker conditions might promote sharing better.
However, unrestricted linking of non-free programs would deprive the users of those programs of all
benefit from the free status of the libraries themselves. This Library General Public License is intended
to permit developers of non-free programs to use free libraries, while preserving your freedom as a
user of such programs to change the free libraries that are incorporated in them. (We have not seen
how to achieve this as regards changes in header files, but we have achieved it as regards changes in
the actual functions of the Library.) The hope is that this will lead to faster development of free
libraries.
The precise terms and conditions for copying, distribution and modification follow. Pay close attention
to the difference between a "work based on the library" and a "work that uses the library". The former
contains code derived from the library, while the latter only works together with the library.
Note that it is possible for a library to be covered by the ordinary General Public License rather than by
this special one.
