GNU LESSER GENERAL PUBLIC LICENSE
Version 2.1, February 1999
Copyright (C) 1991, 1999 Free Software Foundation, Inc.
51 Franklin Street, 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 Lesser GPL. It also counts as the successor of the GNU Library Public License, version 2,
hence the version number 2.1.]
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 Lesser General Public License, applies to some specially designated software packages--typically libraries--of
the Free Software Foundation and other authors who decide to use it. You can use it too, but we suggest you first think carefully
about whether this license or the ordinary General Public License is the better strategy to use in any particular case, based on
the explanations below.
When we speak of free software, we are referring to freedom of use, 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 and use pieces of it in new free programs; and
that you are informed that you can do these things.
To protect your rights, we need to make restrictions that forbid distributors to deny you these rights or to ask you to surrender
these 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 other code 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.
We protect your rights with a two-step method: (1) we copyright the library, and (2) we offer you this license, which gives you
legal permission to copy, distribute and/or modify the library.
To protect each distributor, we want to make it very clear that there is no warranty for the free library.
Also, if the library is modified by someone else and passed on, the recipients should know that what they have is not the original
version, so that the original author’s reputation will not be affected by problems that might be introduced by others.
Finally, software patents pose a constant threat to the existence of any free program. We wish to make sure that a company
cannot effectively restrict the users of a free program by obtaining a restrictive license from a patent holder. Therefore, we insist
that any patent license obtained for a version of the library must be consistent with the full freedom of use specified in this
license.
Most GNU software, including some libraries, is covered by the ordinary GNU General Public License.
This license, the GNU Lesser General Public License, applies to certain designated libraries, and is quite different from the
ordinary General Public License. We use this license for certain libraries in order to permit linking those libraries into non-free
programs.
When a program is linked with a library, whether statically or using a shared library, the combination of the two is legally speaking
a combined work, a derivative of the original library. The ordinary General Public License therefore permits such linking only if the
entire combination fits its criteria of freedom. The Lesser General Public License permits more lax criteria for linking other code
with the library.
We call this license the “Lesser” General Public License because it does Less to protect the user’s freedom than the ordinary
General Public License. It also provides other free software developers Less of an advantage over competing non-free programs.
These disadvantages are the reason we use the ordinary General Public License for many libraries. However, the Lesser license
provides advantages in certain special circumstances.
For example, on rare occasions, there may be a special need to encourage the widest possible use of a certain library, so that it
becomes a de-facto standard. To achieve this, non-free programs must be allowed to use the library. A more frequent case is
that a free library does the same job as widely used non-free libraries. In this case, there is little to gain by limiting the free library
to free software only, so we use the Lesser General Public License.
In other cases, permission to use a particular library in non-free programs enables a greater number of people to use a large
body of free software. For example, permission to use the GNU C Library in non-free programs enables many more people to
use the whole GNU operating system, as well as its variant, the GNU/Linux operating system.
Although the Lesser General Public License is Less protective of the users’ freedom, it does ensure that the user of a program
that is linked with the Library has the freedom and the wherewithal to run that program using a modified version of the Library.
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, whereas the
latter must be combined with the library in order to run.
