it was created to embody and defend a set of principles that were set

forth at the founding of the GNU project and the Free Software Foundation

(FSF)---the organization that upholds, defends and promotes the philosophy

of software freedom.  A prerequisite for understanding the GPL and its

terms and conditions is a basic understanding of the principles behind it.

The GPL is unlike almost all other software licenses in that it is

designed to defend and uphold these principles.

\section{The Free Software Definition}

\label{Free Software Definition}

The Free Software Definition is set forth in full on FSF's website at

A particular program is Free Software if it grants a particular user of

that program, the following freedoms:

\begin{itemize}

\item the freedom to run the program for any purpose.

\item the freedom to change and modify the program.

\item the freedom to copy and share the program.

The focus on ``a particular user'' is very pertinent here.  It is not

uncommon for the same version of a specific program to grant these

freedoms to some subset of its user base, while others have none or only

some of these freedoms.  Section~\ref{Proprietary Relicensing} talks in

detail about how this can happen even if a program is released under the

GPL\@.

Some people refer to software that gives these freedoms as ``Open

Source''.  Besides having a different political focus than those who call

it Free Software\footnote{The political differences between the Free

Software Movement and the Open Source Movement are documented on FSF's

website at

those who call the software ``Open Source'' are focused on a side issue.

User access to the source code of a program is a prerequisite to make use

of the freedom to modify.  However, the important issue is what freedoms

are granted in the license of that source code.  Microsoft's ``Shared

Source'' program, for example, gives various types of access to source

code, but almost none of the freedoms described in this section.

One key issue that is central to these freedoms is that there are no

restrictions on how these freedoms can be exercised.  Specifically, users

and programmers can exercise these freedoms non-commercially or

commercially.  Licenses that grant these freedoms for non-commercial

activities but prohibit them for commercial activities are considered

programmers who might altruistically assist them to modify their software.

The commercial exercise of this freedom is also essential for users.  Each

user, or group of users, must have the right to hire anyone they wish in a

competitive free market to modify and change the software.  This means

that companies have a right to hire anyone they wish to modify their Free

Software.  Additionally, such companies may contract with other companies

to commission software modification.

\subsection{The Freedom to Copy and Share}

Users may share Free Software in a variety of ways.  Free Software

age: choosing between obeying a software license, and friendship (by

giving away a copy of a program your friend who likes the software you are

using).  Free Software licenses, therefore, must permit this sort of

altruistic sharing of software among friends.

The commercial environment must also have the benefits of this freedom.

Commercial sharing typically takes the form of selling copies of Free

Software.  Free Software can be sold at any price to anyone.  Those who

redistribute Free Software commercially have the freedom to selectively

distribute (you can pick your customers) and to set prices at any level

the redistributor sees fit.

The last section set forth the freedoms and rights are respected by Free

Software.  It presupposed, however, that such software exists.  This

section discusses how Free Software comes into existence.  But first, it

addresses how software can be non-free in the first place.

Software can be made proprietary only because it is governed by copyright

law\footnote{This statement is a bit of an oversimplification.  Patents

  and trade secrets can cover software and make it effectively non-free,

  one can contract away their rights and freedoms regarding software, or

  source code can be practically obscured in binary-only distribution

  without reliance on any legal system.  However, the primary control

  mechanism for software is copyright.}.  Copyright law, with respect to

software\footnote{Copyright law in general also governs ``public

  performance'' of copyrighted works.  There is no generally agreed

  definition for public performance of software and version 2 of the GPL

  does not govern public performance.}.  By law, the copyright holder (aka

the author) of the work controls how others may copy, modify and/or

distribute the work.  For proprietary software, these controls are used to

prohibit these activities.  In addition, proprietary software distributors

further impede modification in a practical sense by distributing only

binary code and keeping the source code of the software secret.

Copyright law is a construction.  In the USA, the Constitution permits,

but does not require, the creation of copyright law as federal

software into a file.

However, an author can disclaim that default control given to her by the

copyright laws.  Once this is done, the software is in the public domain

--- it is no longer covered by copyright.  Since it is copyright law that

allows for various controls on software (i.e., prohibition of copying,

modification, and redistribution), removing the software from the

copyright system and placing it into the public domain does yield Free

Software.

Carefully note that software in the public domain is \emph{not} licensed

in any way.  It is nonsensical to say software is ``licensed for the

expressed permission to take actions governed by copyright law.

By contrast, what the copyright holder has done is renounce her copyright

controls on the work.  The law gave her controls over the work, and she

has chosen to waive those controls.  Software in the public domain is

absent copyright and absent a license.  The software freedoms discussed in

Section~\ref{Free Software Definition} are all granted because there is no

legal system in play to take them away.

\subsection{Why Copyright Free Software?}

If simply disclaiming copyright on software yields Free Software, then it

feeds the proprietary software.  The public commons disappears, because

fewer and fewer entities have an incentive to contribute back to the

commons.  They know that any of their competitors can proprietarize their

enhancements.  Over time, almost no interesting work is left in the public

domain, because nearly all new work is done by proprietarization.

A legal mechanism is needed to redress this problem.  FSF was in fact

originally created primarily as a legal entity to defend software freedom,

and that work of of defending software freedom is a substantial part of

its work today.  Specifically because of this ``embrace, proprietarize and

extend'' cycle, FSF made a conscious choice to copyright its Free Software,

and then license it under ``copyleft'' terms, and many, including the

Copyleft is a legal strategy to defend, uphold and propagate software

freedom.  The basic technique of copyleft is as follows: copyright the

software, license it under terms that give all the software freedoms, but

use the copyright law controls to ensure that all who receive a copy of

the software have equal rights and freedom.  In essence, copyleft grants

freedom, but forbids others to forbid that freedom from anyone else along

the distribution and modification chains.

Copyleft is a general concept.  Much like ideas for what a computer might

do must be \emph{implemented} by a program that actually does the job, so

too must copyleft be implemented in some concrete legal structure.

By the same token, nearly all established GPL'ed software systems have a

vibrant commercial community.  Nearly every GPL'ed system that has gained

wide adoption from non-commercial users and developers eventually begins

to fuel a commercial system around that software.

For example, consider the Samba file server system that allows Unix-like

systems (including GNU/Linux) to serve files to Microsoft Windows systems.

Two graduate students originally developed Samba in their spare time and

it was deployed non-commercially in academic environments.  However, very

soon for-profit companies discovered that the software could work for them

as well, and their system administrators began to use it in place of

Microsoft Windows NT file-servers.  This served to lower the cost of

The non-commercial users, however, were not concerned when these two

fellows began collecting paychecks off of their GPL'ed work.  They knew

that because of the nature of the GPL that improvements that were

distributed in the commercial environment could easily be folded back into

the standard version.  Companies are not permitted to proprietarize

Samba, so the non-commercial users, and even other commercial users are

safe in the knowledge that the software freedom ensured by GPL will remain

protected.

Commercial developers also work in concert with non-commercial developers.

Those two now-long-since graduated students continue to contribute to

creation of this vibrant commercial and non-commercial Free Software

economy.

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

\chapter{Copying, Modifying and Redistributing}

This chapter begins the deep discussion of the details of the terms of

GPL\@.  In this chapter, we consider the core terms: GPL \S\S 0--3.  These

are the sections of the GPL that fundamentally define the legal details of

how software freedom is respected.

\section{GPL \S 0: Freedom to Run}

\S 0, the opening section of GPL, sets forth that the work is governed by

copyright law.  It specifically points out that it is the ``copyright

holder'' who decides if a work is licensed under its terms, and explains

how the copyright holder might indicate this fact.

A bit more subtly, \S 0 makes an inference that copyright law is the only

system under which it is governed.  Specifically, it states:

\begin{quote}

Activities other than copying, distribution and modification are not

covered by this License; they are outside its scope.

\end{quote}

to fair and unregulated uses.

Fair use of copyrighted material is an established legal doctrine that

permits certain activities.  Discussion of the various types of fair use

activity are beyond the scope of this tutorial.  However, one important

example of fair use is the right to quote a very few lines (less than

seven or so), and reuse them as you with without licensing restrictions.

Fair use is a doctrine established by the courts or by statute.  By

contrast, unregulated uses are those that are not covered by the statue

nor determined by a court to be covered, but are common and enjoyed by

many users.  An example of unregulated use is reading a printout of the

how to be a better programmer.

\medskip

Thus, the GPL protects users fair and unregulated use rights precisely by

not attempting to cover them.  Furthermore, the GPL ensures the freedom

to run specifically by stating the following:

\begin{quote}

The act of running the Program is not restricted

\end{quote}

Thus, users are explicitly given the freedom to run by \S 0.

\medskip

The bulk of \S 0 not yet discussed gives definitions for other terms used

throughout.  The only one worth discussing in detail is ``work based on

the Program''.  The reason this definition is particularly interesting is

not for the definition itself, which is rather straightforward, but the

because it clears up a common misconception about the GPL\@.

The GPL is often mistakenly criticized because it fails to give a

definition of ``derivative work''.  In fact, it would be incorrect and

fact, has no control over what may or may not be a derivative work.  This

matter is left up to copyright law, not the licenses that utilize it.

It is certainly true that copyright law as a whole does not propose clear

and straightforward guidelines for what is and is not a derivative

software work under copyright law.  However, no copyright license --- not

even the GNU GPL -- can be blamed for this.  Legislators and court

opinions must give us guidance to decide the border cases.

\section{GPL \S 1: Verbatim Copying}

GPL \S 1 covers the matter of redistributing the source code of a program

exactly as it was received.  This section is quite straightforward.

However, there are a few details worth noting here.

The phrase ``in any medium'' is important.  This, for example, gives the

freedom to publish a book that is the printed copy of the program's source

code.  It also allows for changes in the medium of distribution.  Some

vendors may ship Free Software on a CD, but others may place it right on

the hard drive of a pre-installed computer.  Any such redistribution media

is allowed.

on making a profit from Free Software redistribution.)

\section{GPL \S 2: Share and Share Alike}

For many, this is where the ``magic'' happens that defends software

freedom along the distribution chain.  \S 2 is the only place in the GPL

that governs the modification controls of copyright law.  If someone

modifies a GPL'ed program, she is bound in the making those changes by \S

2.  The goal here is to ensure that the body of GPL'ed software, as it

continues and develops, remains Free as in freedom.

To achieve that goal, \S 2 first sets forth that the rights of

copying, as presented in \S 1.  Therefore, the details of charging,

keeping copyright notices intact, and other \S 1 provisions are in tact

here as well.  However, there are three additional requirements.

The first (\S 2(a)) requires that modified files carry ``prominent

notices'' explaining what changes were made and the date of such changes.

The goal here is not to put forward some specific way of marking changes,

or controlling the process of how changes get made.  Primarily, \S 2(a)

seeks to ensure that those receiving modified versions know what path it

took to them.  For some users, it is important to know that they are using

the standard version of program, because while there are many advantages

to using a fork, there are a few disadvantages.  Users should be informed

\medskip

The second requirement (\S 2(b)) contains the four short lines that embody

the legal details of ``share and share alike''.  These 46 words are

considered by some to be the most worthy of careful scrutiny.  It is worth

the effort to carefully understand what each clause is saying, because \S

2(b) can be a source of great confusion when not properly understood.

In considering \S 2(b), first note the qualifier: it only applies to

derivative works that ``you distribute or publish''.  Despite years of

education efforts by FSF on this matter, many still believe that modifiers