Operation Manual

233
Appendix
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.