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System Administrator Guide
C-21
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.