establish such practices before building a product based on GPL'd

software.\footnote{This document addresses compliance with GPLv2,

  GPLv3, LGPLv2, and LGPLv3.  Advice on avoiding the most common

  errors differs little for compliance with these four licenses.

  \S~\ref{lgpl} discusses the key differences between GPL and LGPL

  compliance.}

\section{Evaluate License Applicability}

\label{derivative-works}

Political discussion about the GPL often centers around the ``copyleft''

requirements of the license.  Indeed, the license was designed primarily

to embody this licensing feature.  Most companies adding non-trivial

  discussion regarding copyleft and derivative works.  In practical

  reality, this issue is not relevant to the vast majority of companies

However, in our experience with GPL enforcement, few redistributors'

compliance challenges relate directly to the copyleft provisions; this is

doubly true for most embedders.  Instead, the distributions of GPL'd

systems that we encounter typically consist of a full operating system

including components under the GPL (e.g., Linux, BusyBox) and components

under the LGPL (e.g., the GNU C Library).  Sometimes, these programs have

been patched or slightly improved by direct modification of their sources,

resulting unequivocally in a derivative work.  Alongside these programs,

companies often distribute fully independent, proprietary programs,

developed from scratch, which are designed to run on the Free Software operating

system but do not combine with, link to, modify, or otherwise derive from

Note finally that GPLv2~\S1 creates groundwork for the important defense of

commercial freedom.  GPLv2~\S1 clearly states that in the case of verbatim

copies, one may make money.  Re distributors are fully permitted to charge

for the redistribution of copies of Free Software. In addition, they may

provide the warranty protection that the GPL disclaims as an additional

service for a fee. (See Section~\ref{Business Models} for more discussion

on making a profit from Free Software redistribution.)

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\chapter{Derivative Works: Statute and Case Law}

We digress for this chapter from our discussion of GPL's exact text to

consider the matter of derivative works --- a concept that we must

understand fully before considering GPLv2~\S\S2--3\@. GPL, and Free

Software licensing in general, relies critically on the concept of

``derivative work'' since software that is ``independent,'' (i.e., not

``derivative'') of Free Software need not abide by the terms of the

applicable Free Software license. As much is required by \S~106 of the

Copyright Act, 17 U.S.C. \S~106 (2002), and admitted by Free Software

licenses, such as the GPL, which (as we have seen) states in GPLv2~\S0 that ``a

`work based on the Program' means either the Program or any derivative

work under copyright law.'' It is being a derivative work of Free Software