\tableofcontents

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\pagenumbering{arabic}

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\chapter{What Is Free Software?}

Consideration of the GNU General Public License (herein, abbreviated as

\defn{GNU GPL} or just \defn{GPL}) must begin by first considering the broader

world of Free Software.  The GPL was not created from a void, rather,

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.

\item the freedom to share improved versions of the program.

\end{itemize}

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

non-Free.

In general, software for which most or all of these freedoms are

restricted in any way is called ``non-Free Software''.  Typically, the

term ``proprietary software'' is used more or less interchangeably with

``non-Free Software''.  Personally, I tend to use the term ``non-Free

Software'' to refer to non-commercial software that restricts freedom

(such as ``shareware'') and ``proprietary software'' to refer to

commercial software that restricts freedom (such as nearly all of

Microsoft's and Oracle's offerings).

The remainder of this section considers each of the four freedoms in

Free Software programs allow users to change, modify and adapt the

software to suit their needs.  Access to the source code and related build

scripts are an essential part of this freedom.  Without the source code

and the ability to build the binary applications from that source, the

freedom cannot be properly exercised.

Programmers can take direct benefit from this freedom, and often do.

However, this freedom is also important to users who are not programmers.

Users must have the right to exercise this freedom indirectly in both

commercial and non-commercial settings.  For example, users often seek

non-commercial help with the software on email lists and in users groups.

When they find such help, they must have the freedom to recruit

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.

It is true that many people get copies of Free Software very cheaply (and

sometimes without charge). The competitive free market of Free Software

tends to keep prices low and reasonable.  However, if someone is willing

to pay a billion dollars for one copy of the GNU Compiler Collection, such

a sale is completely permitted.

Another common instance of commercial sharing is service-oriented

distribution.  For example, a distribution vendor may provide immediate

security and upgrade distribution via a special network service.  Such

distribution is completely permitted for Free Software.

(Section~\ref{Business Models} of this tutorial talks in detail about

Companies and individuals have the right to make true value-added versions

of Free Software.  They may use freedom to share improvements to

distribute distinct versions of Free Software with different functionality

and features.  Furthermore, this freedom can be exercised to serve a

disenfranchised subset of the user community.  If the developers of the

standard version refuse to serve the needs of some of the software's

users, other entities have the right to create long- or short-lived fork

that serves that sub-community.

\section{How Does Software Become Free?}

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

legislation.  Software, since it is an idea fixed in a tangible medium, is

thus covered by the statues, and is copyrighted by default.

However, this legal construction is not necessarily natural.  Software, in

its natural state without copyright, is Free Software.  In an imaginary

world, which has no copyright, the rules would be different.  In this

world, when you received a copy of a program's source code, there would be

no default legal system to restrict you from sharing it with others,

making modifications, or redistributing those modified

versions\footnote{There could still exist legal systems, like our modern

  patent system, which could restrict the software in other ways.}.

the domain of the copyright system.  A copyright holder is always

permitted to \defn{disclaim} their copyright.  If copyright is disclaimed,

the software is not governed by copyright law.  Software not governed by

copyright is in the ``public domain''.

\subsection{Public Domain Software}

An author can create public domain software by disclaiming all copyright

interest on the work.  In the USA and other countries that have signed the

Berne convention on copyright, software is copyrighted automatically by

the author when she ``fixes the software into a tangible medium''.  In

the software world, this usually means typing the source code of the

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

stands to reason that putting software into the public domain is the

easiest and most straightforward way to produce Free Software.  Indeed,

some major Free Software projects have chosen this method for making their

software Free.  However, most of the Free Software in existence \emph{is}

copyrighted.  In most cases (particularly in that of FSF and the GNU

Project), this was done due to very careful planning.

Software released into the public domain does grant freedom to those users

who receive the standard versions on which the original author disclaimed

copyright.  However, since the work is not copyrighted, any non-trivial

modification made to the work is fully copyrightable.

Free Software released into the public domain initially is Free, and

perhaps some who modify the software choose to place their work into the

public domain as well.  However, over time, some entities will choose to

proprietarize their modified versions.  The public domain body of software

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.

``Share and share alike'' is a phrase that is often enough to explain the

concept behind copyleft, but to actually make it work in the real world, a

true implementation in legal text must exist.  The GPL is the primary

implementation of copyleft in copyright licensing language.

\section{An Ecosystem of Equality}

The GPL uses copyright law to defend freedom and equally ensure users'

rights.  This ultimately creates an ecosystem of equality for both

business and non-commercial users.

\subsection{The Non-Commercial Ecosystem}

developers fail to address their needs or abandon the project, the GPL

ensures that someone else has the right to pick up development.

Developers know that the users cannot redistribute their software without

passing along the rights granted by GPL, so they are assured that every

one of their users is treated equally.

Because of the symmetry and fairness inherent in GPL'ed distribution,

nearly every GPL'ed package in existence has a vibrant non-commercial user

and developer base.

\subsection{The Commercial Ecosystem}

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

Samba altruistically, but also get work doing it.  Priorities change when a

client is in the mix, but all the code is contributed back to the

standard version.  Meanwhile, many other individuals have gotten involved

non-commercially as developers, because they want to ``cut their teeth on

Free Software'' or because the problems interest them.  When they get good

at it, perhaps they will move on to another project or perhaps they will

become commercial developers of the software themselves.

No party is a threat to another in the GPL software scenario because

everyone is on equal ground.  The GPL protects rights of the commercial

and non-commercial contributors and users equally.  The GPL creates trust,

because it is a level playing field for all.

    License'', version 1.0} or any later version as published by Creative

  Commons.}

\end{quotation}

In essence, lawyers are paid to service the shared commons of legal

infrastructure.  Few citizens defend themselves in court or write their

own briefs (even though they are legally permitted to do so) because

everyone would prefer to have an expert do that job.

The Free Software economy is a market that is ripe for experts.  It

functions similarly to other well established professional fields like the

law.  The GPL, in turn, serves as the legal scaffolding that permits the

creation of this vibrant commercial and non-commercial Free Software

economy.

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\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}

In essence, the license governs \emph{only} those activities and all other

activities are unrestricted, provided that no other agreements trump GPL

(which they cannot; see Sections~\ref{GPLs6} and~\ref{GPLs7}).  This is

very important, because the Free Software community heavily supports

users' rights to ``fair use'' and ``unregulated use'' of copyrighted

material.  GPL asserts through this clause that it supports users' rights

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.

Preservation of copyright notice and license notifications are mentioned

specifically in \S 1.  These are in some ways the most important part of

the redistribution, which is why they are mentioned by name.  The GPL

always strives to make it abundantly clear to anyone who receives the

software what its license is.  The goal is to make sure users know their

rights and freedoms under GPL and to leave no reason that someone would be

surprised that the software she got was licensed under GPL\@.  Thus

throughout the GPL, there are specific reference to the importance of

notifying others down the distribution chain that they have rights under

GPL.

Also mentioned by name is the warranty disclaimer.  Most people today do

adoption), there are little or no implied warranties with software.

However, just to be on the safe side, GPL clearly disclaims them, and the

GPL requires redistributors to keep the disclaimer very visible.  (See

Sections~\ref{GPLs11} and~\ref{GPLs12} of this tutorial for more on GPL's

warranty disclaimers.)

Note finally that \S 1 begins to set forth the important defense of

commercial freedom.  \S 1 clearly states that in the case of verbatim

copies, one may make money.  Redistributors 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.)

\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

of GPL'ed software are required by the license to publish or otherwise

share their changes.  On the contrary, \S 2(b) {\bf does not apply if} the

changes are never distributed.  Indeed, the freedom to make private,

personal, unshared changes to software for personal use only should be

protected and defended\footnote{FSF does maintain that there is an {\bf

    ethical} obligation to redistribute changes that are generally useful,

  and often encourages companies and individuals to do so.  However, there

  is a clear distinction between what one {\bf ought} to do and what one

  {\bf must} do.}.

Next, we again encounter the same matter that appears in \S 0, in the

following text: