User Manual

44
LGPLv2 / LGPLv2+ to GPLv2 / GPLv2+ to LGPLv2.1 / LGPLv2.1+
GNU LIBRARY GENERAL PUBLIC LICENSE
Version 2, June 1991
Copyright (C) 1991 Free Software Foundation, Inc.
51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA
Everyone is permitted to copy and distribute verbatim copies
of this license document, but changing it is not allowed.
[This is the first released version of the library GPL. It is
numbered 2 because it goes with version 2 of the ordinary GPL.]
Preamble
The licenses for most software are designed to take away your freedom to share and
change it. By contrast, the GNU General Public Licenses are intended to guarantee
your freedom to share and change free software--to make sure the software is free for
all its users.
This license, the Library General Public License, applies to some specially designated
Free Software Foundation software, and to any other libraries whose authors decide
to use it. You can use it for your libraries, too.
When we speak of free software, we are referring to freedom, not price. Our General
Public Licenses are designed to make sure that you have the freedom to distribute
copies of free software (and charge for this service if you wish), that you receive source
code or can get it if you want it, that you can change the software or use pieces of it
in new free programs; and that you know you can do these things.
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.