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

features (beyond mere porting and bug-fixing) to GPL'd software (and

thereby invoking these requirements) are already well aware of their

more complex obligations under the license.\footnote{While, there has been much legal

  discussion regarding copyleft and derivative works.  In practical

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

  distributing GPL'd software.  Those interested in this issue should study

  \tutorialpartsplit{\textit{Detailed Analysis of the GNU GPL and Related

      Licenses}'s Section on derivative works}{\S~\ref{derivative-works} of

    this tutorial}.}

However, experienced  GPL enforcers find that few redistributors'

compliance challenges relate directly to the copyleft provisions; this is

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

systems most often encountered 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, derive from, or otherwise

create a combined work with

the GPL'd components.\footnote{However, these programs do often combine

  with LGPL'd libraries. This is discussed in detail in \S~\ref{lgpl}.}

In the latter case, where the work is unquestionably a separate work of

creative expression, no copyleft provisions are invoked.

Admittedly, a tiny

minority of situations which lie outside these two categories, and thus

do involve close questions about derivative and combined works.  Those

situations admittedly do require a highly

fact-dependent analysis and cannot be addressed in a general-purpose

document, anyway.

\medskip

Most companies accused of violations lack a basic understanding

of how to comply even in the former straightforward scenario.  This document

provides those companies with the fundamental and generally applicable prerequisite knowledge.

For answers to rarer and more complicated legal questions, such as whether

your software is a derivative or combined work of some copylefted software, consult

with an attorney.\footnote{If you would like more information on the

  application of derivative works doctrine to software, a detailed legal

  discussion is presented in our colleague Dan Ravicher's article,

  \textit{Software Derivative Work: A Circuit Dependent Determination} and in

  \tutorialpartsplit{\textit{Detailed Analysis of the GNU GPL and Related

      Licenses}'s Section on derivative works}{\S~\ref{derivative-works} of

    this tutorial}.}

This discussion thus assumes that you have already identified the

``work'' covered by the license, and that any components not under the GPL

(e.g., applications written entirely by your developers that merely happen

to run on a Linux-based operating system) distributed in conjunction with

those works are separate works within the meaning of copyright law and the GPL\@.  In

such a case, the GPL requires you to provide complete corresponding

source (CCS)\footnote{For more on CCS,  see

\tutorialpartsplit{\textit{Detailed Analysis of the GNU GPL and Related

      Licenses}'s Section on GPLv2~\S2 and GPLv3~\S1.}{\S~\ref{GPLv2s2} and \S~\ref{GPLv3s1} of

    this tutorial}.}

for the GPL'd components and your modifications thereto, but not

for independent proprietary applications.  The procedures described in

this document address this typical scenario.

\section{Monitor Software Acquisition}

Software engineers deserve the freedom to innovate and import useful

software components to improve products.  However, along with that

freedom should come rules and reporting procedures to make sure that you

are aware of what software that you include with your product.

The most typical response to an initial enforcement action is: ``We

didn't know there was GPL'd stuff in there''.  This answer indicates

failure in the software acquisition and procurement process.  Integration

of third-party proprietary software typically requires a formal

arrangement and management/legal oversight before the developers

incorporate the software.  By contrast, developers often obtain and

integrate Free Software without intervention nor oversight. That ease of acquisition, however,

does not mean the oversight is any less necessary.  Just as your legal

and/or management team negotiates terms for inclusion of any proprietary

software, they should gently facilitate all decisions to bring Free Software into your

product.

Simple, engineering-oriented rules help provide a stable foundation for

Free Software integration.  For example, simply ask your software developers to send an email to a

standard place describing each new Free Software component they add to the system,

and have them include a brief description of how they will incorporate it

into the product.  Further, make sure developers use a revision control

system (such as Git or Mercurial), and have

store the upstream versions of all software in a ``vendor branch'' or

similar mechanism, whereby they can easily track and find the main version

of the software and, separately, any local changes.

Such procedures are best instituted at your project's launch.  Once 

chaotic and poorly-sourced development processes begin, cataloging the

presence of GPL'd components  becomes challenging.

Such a situation often requires use of a tool to ``catch up'' your knowledge

about what software your product includes.  Most commonly, companies choose

some software licensing scanning tool to inspect the codebase.  However,

there are few tools that are themselves Free Software.  Thus, GPL enforcers

usually recommend the GPL'd

\href{http://fossology.org/}{Fossology system}, which analyzes a

source code base and produces a list of Free Software licenses that may apply to

the code.  Fossology can help you build a catalog of the sources you have

already used to build your product.  You can then expand that into a more

structured inventory and process.

\section{Track Your Changes and Releases}

As explained in further detail below, the most important component of GPL

compliance is the one most often ignored: proper inclusion of CCS in all

distributions  of GPL'd

software.  To comply with GPL's CCS requirements, the distributor

\textit{must} always know precisely what sources generated a given binary

distribution.

In an unfortunately large number of our enforcement cases, the violating

company's engineering team had difficulty reconstructing the CCS

for binaries distributed by the company.  Here are three simple rules to

\begin{itemize}

\item Ensure that your

developers are using revision control systems properly.

\item Have developers mark or ``tag'' the full source tree corresponding to

  builds distributed to customers

\item Check that your developers store all parts of the software

development in the revision control system, including {\sc readme}s, build

scripts, engineers' notes, and documentation.

\end{itemize}

Your developers will benefit anyway from these rules.  Developers will be

happier in their jobs if their tools already track the precise version of

source that corresponds to any deployed binary.

\section{Avoid the ``Build Guru''}

Too many software projects rely on only one or a very few team members who

know how to build and assemble the final released product.  Such knowledge

centralization not only creates engineering redundancy issues, but also

thwarts GPL compliance.  Specifically, CCS does not just require source code,

but scripts and other material that explain how to control compilation and

installation of the executable and object code.

Thus, avoid relying on a ``build guru'', a single developer who is the only one

who knows how to produce your final product. Make sure the build process

is well defined.  Train every developer on the build process for the final

binary distribution, including (in the case of embedded software)

generating a final firmware image suitable for distribution to the

customer.  Require developers to use revision control for build processes.

Make a rule that adding new components to the system without adequate

build instructions (or better yet, scripts) is unacceptable engineering

practice.

\chapter{Details of Compliant Distribution}

This section explains the specific requirements placed upon

distributors of GPL'd software.  Note that this section refers heavily to

specific provisions and language in

\href{http://www.gnu.org/licenses/old-licenses/gpl-2.0.html#section3}{GPLv2}

and \href{http://www.fsf.org/licensing/licenses/gpl.html#section6}{GPLv3}.

It may be helpful to have a copy of each license open while reading this

section.

\section{Binary Distribution Permission}

\label{binary-distribution-permission}

% be careful below, you cannot refill the \if section, so don't refill

% this paragraph without care.

The various versions of the GPL are copyright licenses that grant

permission to make certain uses of software that are otherwise restricted

by copyright law.  This permission is conditioned upon compliance with the

GPL's requirements.

This section walks through the requirements (of both GPLv2 and GPLv3) that

apply when you distribute GPL'd programs in binary (i.e., executable or

object code) form, which is typical for embedded applications.  Because a

binary application derives from a program's original sources, you need

permission from the copyright holder to distribute it.  \S~3 of GPLv2 and

\S~6 of GPLv3 contain the permissions and conditions related to binary

distributions of GPL'd programs.\footnote{These sections cannot be fully

  understood in isolation; read the entire license thoroughly before

  focusing on any particular provision.  However, once you have read and

  understood the entire license, look to these sections to guide

  compliance for binary distributions.}

GPL's binary distribution sections offer a choice of compliance methods,

each of which we consider in turn.  Each option refers to the

``Corresponding Source'' code for the binary distribution, which includes

the source code from which the binary was produced.  This abbreviated and

simplified definition is sufficient for the binary distribution discussion

in this section, but you may wish to refer back to this section after

reading the thorough discussion of ``Corresponding Source'' that appears

in \S~\ref{corresponding-source}.

\subsection{Option (a): Source Alongside Binary}

GPLv2~\S~3(a) and v3~\S~6(a) embody the easiest option for providing

source code: including Corresponding Source with every binary

distribution.  While other options appear initially less onerous, this

option invariably minimizes potential compliance problems, because when

you distribute Corresponding Source with the binary, \emph{your GPL

  obligations are satisfied at the time of distribution}.  This is not

true of other options, and for this reason, we urge you to seriously

consider this option.  If you do not, you may extend the duration of your

obligations far beyond your last binary distribution.

Compliance under this option is straightforward.  If you ship a product

that includes binary copies of GPL'd software (e.g., in firmware, or on a

hard drive, CD, or other permanent storage medium), you can store the

Corresponding Source alongside the binaries.  Alternatively, you can

include the source on a CD or other removable storage medium in the box

containing the product.

GPLv2 refers to the various storage mechanisms as ``medi[a] customarily

used for software interchange''.  While the Internet has attained primacy

as a means of software distribution where super-fast Internet connections

are available, GPLv2 was written at a time when downloading software was

not practical (and was often impossible).  For much of the world, this

condition has not changed since GPLv2's publication, and the Internet

still cannot be considered ``a medium customary for software

interchange''.  GPLv3 clarifies this matter, requiring that source be

``fixed on a durable physical medium customarily used for software

interchange''.  This language affirms that option (a) requires binary

redistributors to provide source on a physical medium.

Please note that while selection of option (a) requires distribution on a

physical medium, voluntary distribution via the Internet is very useful.  This

is discussed in detail in \S~\ref{offer-with-internet}.

\subsection{Option (b): The Offer}

\label{offer-for-source}

Many distributors prefer to ship only an offer for source with the binary

distribution, rather than the complete source package.  This

option has value when the cost of source distribution is a true

per-unit cost.  For example, this option might be a good choice for

embedded products with permanent storage too small to fit the source, and

which are not otherwise shipped with a CD but \emph{are} shipped with a

manual or other printed material.

However, this option increases the duration of your obligations

dramatically.  An offer for source must be good for three full years from

your last binary distribution (under GPLv2), or your last binary or spare

\tutorialpartsplit{as discussed in \textit{A Practical Guide to GPL

    Compliance}, there are }{Chapter~\ref{compliance-understanding-whos-enforcing}

  explains further} key differences between these two very different uses of GPL.

\section{GPLv2~\S5: Acceptance, Copyright Style}

\label{GPLv2s5}

GPLv2~\S5 brings us to perhaps the most fundamental misconception and common

confusion about GPLv2\@. Because of the prevalence of proprietary software,

most users, programmers, and lawyers alike tend to be more familiar with

EULAs. EULAs are believed by their authors to be contracts, requiring

formal agreement between the licensee and the software distributor to be

valid. This has led to mechanisms like ``shrink-wrap'' and ``click-wrap''

as mechanisms to perform acceptance ceremonies with EULAs.

The GPL does not need contract law to ``transfer rights.''  Usually, no rights

are transferred between parties.  By contrast, the GPL is primarily a permission

slip to undertake activities that would otherwise have been prohibited

by copyright law.  As such, GPL needs no acceptance ceremony; the

licensee is not even required to accept the license.

However, without the GPL, the activities of copying, modifying and

distributing the software would have otherwise been prohibited.  So, the

GPL says that you only accepted the license by undertaking activities that

you would have otherwise been prohibited without your license under GPL\@.

This is a certainly subtle point, and requires a mindset quite different

from the contractual approach taken by EULA authors.

An interesting side benefit to GPLv2~\S5 is that the bulk of users of Free

Software are not required to accept the license.  Undertaking fair and

unregulated use of the work, for example, does not bind you to the GPL,

since you are not engaging in activity that is otherwise controlled by

copyright law.  Only when you engage in those activities that might have an

impact on the freedom of others does license acceptance occur, and the

terms begin to bind you to fair and equitable sharing of the software.  In

other words, the GPL only kicks in when it needs to for the sake of

freedom.

While GPL is by default a copyright license, it is certainly still possible

to consider GPL as a contract as well.  For example, some distributors chose

to ``wrap'' their software in an acceptance ceremony to the GPL, and nothing in

the GPL prohibits that use.  Furthermore, the ruling in \textit{Jacobsen

  v. Katzer, 535 F.3d 1373, 1380 (Fed.Cir.2008)} indicates that \textbf{both}

copyright and contractual remedies may be sought by a copyright holder

seeking to enforce a license designed to uphold software freedom.

% FIXME-LATER: Write this

%\section{Using GPL Both as a Contract and Copyright License}

\section{GPLv2~\S6: GPL, My One and Only}

\label{GPLv2s6}

A point that was glossed over in Section~\ref{GPLv2s4}'s discussion of GPLv2~\S4

was the irrevocable nature of the GPL\@. The GPLv2 is indeed irrevocable,

and it is made so formally by GPLv2~\S6.

The first sentence in GPLv2~\S6 ensures that as software propagates down the

distribution chain, that each licensor can pass along the license to each

new licensee.  Under GPLv2~\S6, the act of distributing automatically grants a

license from the original licensor to the next recipient.  This creates a

chain of grants that ensure that everyone in the distribution has rights

under the GPLv2\@.  In a mathematical sense, this bounds the bottom ---

making sure that future licensees get no fewer rights than the licensee before.

The second sentence of GPLv2~\S6 does the opposite; it bounds from the top.  It

prohibits any licensor along the distribution chain from placing

additional restrictions on the user.  In other words, no additional

requirements may trump the rights and freedoms given by GPLv2\@.

The final sentence of GPLv2~\S6 makes it abundantly clear that no individual

entity in the distribution chain is responsible for the compliance of any

other.  This is particularly important for noncommercial users who have

passed along a source offer under GPLv2~\S3(c), as they cannot be assured that

the issuer of the offer will honor their GPLv2~\S3 obligations.

In short, GPLv2~\S6 says that your license for the software is your one and

only copyright license allowing you to copy, modify and distribute the

software.

\section{GPLv2~\S7: ``Give Software Liberty or Give It Death!''}

\label{GPLv2s7}

In essence, GPLv2~\S7 is a verbosely worded way of saying for non-copyright

systems what GPLv2~\S6 says for copyright.  If there exists any reason that a

distributor knows of that would prohibit later licensees from exercising

their full rights under GPL, then distribution is prohibited.

Originally, this was designed as the title of this section suggests --- as

a last ditch effort to make sure that freedom was upheld.  However, in

modern times, it has come to give much more.  Now that the body of GPL'd

software is so large, patent holders who would want to be distributors of

GPL'd software have a tough choice.  They must choose between avoiding

distribution of GPL'd software that exercises the teachings of their

patents, or grant a royalty-free, irrevocable, non-exclusive license to

those patents.  Many companies have chosen the latter.

Thus, GPLv2~\S7 rarely gives software death by stopping its distribution.

Instead, it is inspiring patent holders to share their patents in the same

freedom-defending way that they share their copyrighted works.

\section{GPLv2~\S8: Excluding Problematic Jurisdictions}

\label{GPLv2s8}

GPLv2~\S8 is rarely used by copyright holders.  Its intention is that if a

particular country, say Unfreedonia, grants particular patents or allows

copyrighted interfaces (no country to our knowledge even permits those

yet), that the GPLv2'd software can continue in free and unabated

distribution in the countries where such controls do not exist.

As far as is currently known, GPLv2~\S8 has very rarely been formally used by

copyright holders.  Admittedly, some have used GPLv2~\S8 to explain various

odd special topics of distribution (usually related in some way to

GPLv2~\S7).  However, generally speaking, this section is not proven

particularly useful in the more than two decades of GPLv2 history.

Meanwhile, despite many calls by the FSF (and others) for those licensors who

explicitly use this section to come forward and explain their reasoning, no

one ever did.  Furthermore, research conducted during the GPLv3 drafting

process found exactly one licensor who had invoked this section to add an

explicit geographical distribution limitation, and the reasoning for that one

invocation was not fitting with FSF's intended spirit of GPLv2~\S8.  As such,

GPLv2~\S8 was not included at all in GPLv3.

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

\chapter{Odds, Ends, and Absolutely No Warranty}

GPLv2~\S\S0--7 constitute the freedom-defending terms of the GPLv2.  The remainder

liability.

\section{GPLv2~\S9: FSF as Stewards of GPL}

\label{GPLv2s9}

FSF reserves the exclusive right to publish future versions of the GPL\@;

GPLv2~\S9 expresses this.  While the stewardship of the copyrights on the body

of GPL'd software around the world is shared among thousands of

individuals and organizations, the license itself needs a single steward.

Forking of the code is often regrettable but basically innocuous.  Forking

of licensing is disastrous.

(Chapter~\ref{tale-of-two-copylefts} discusses more about the various

versions of GPL.)

\section{GPLv2~\S10: Relicensing Permitted}

\label{GPLv2s10}

GPLv2~\S10 reminds the licensee of what is already implied by the nature of

copyright law.  Namely, the copyright holder of a particular software

program has the prerogative to grant alternative agreements under separate

copyright licenses.

\section{GPLv2~\S11: No Warranty}

\label{GPLv2s11}

Most warranty disclaimer language shout at you.  The

\href{http://www.law.cornell.edu/ucc/2/2-316}{Uniform Commercial

  Code~\S2-316} requires that disclaimers of warranty be ``conspicuous''.

There is apparently general acceptance that \textsc{all caps} is the

preferred way to make something conspicuous, and that has over decades worked

its way into the voodoo tradition of warranty disclaimer writing.

That said, there is admittedly some authority under USA law suggesting that

effective warranty disclaimers that conspicuousness can be established by

capitalization and is absent when a disclaimer has the same typeface as the

terms surrounding it (see \textit{Stevenson v.~TRW, Inc.}, 987 F.2d 288, 296

(5th Cir.~1993)).  While GPLv3's drafters doubted that such authority would

apply to copyright licenses like the GPL, the FSF has nevertheless left

warranty and related disclaimers in \textsc{all caps} throughout all versions

of GPL\@\footnote{One of the authors of this tutorial, Bradley M.~Kuhn, has

  often suggested the aesthetically preferable compromise of a

  \textsc{specifically designed ``small caps'' font, such as this one, as an

    alternative to} WRITING IN ALL CAPS IN THE DEFAULT FONT (LIKE THIS),

  since the latter adds more ugliness than conspicuousness.  Kuhn once

  engaged in reversion war with a lawyer who disagreed, but that lawyer never

  answered Kuhn's requests for case law that argues THIS IS INHERENTLY MORE

  CONSPICUOUS \textsc{Than this is}.}.

Some have argued the GPL is unenforceable in some jurisdictions because

its disclaimer of warranties is impermissibly broad.  However, GPLv2~\S11

contains a jurisdictional savings provision, which states that it is to be

interpreted only as broadly as allowed by applicable law.  Such a

provision ensures that both it, and the entire GPL, is enforceable in any

jurisdiction, regardless of any particular law regarding the

permissibility of certain warranty disclaimers.

Finally, one important point to remember when reading GPLv2~\S11 is that GPLv2~\S1

permits the sale of warranty as an additional service, which GPLv2~\S11 affirms.

\section{GPLv2~\S12: Limitation of Liability}

\label{GPLv2s12}

There are many types of warranties, and in some jurisdictions some of them

cannot be disclaimed.  Therefore, usually agreements will have both a

warranty disclaimer and a limitation of liability, as we have in GPLv2~\S12.

GPLv2~\S11 thus gets rid of all implied warranties that can legally be

disavowed. GPLv2~\S12, in turn, limits the liability of the actor for any

warranties that cannot legally be disclaimed in a particular jurisdiction.

Again, some have argued the GPL is unenforceable in some jurisdictions

because its limitation of liability is impermissibly broad. However, \S

12, just like its sister, GPLv2~\S11, contains a jurisdictional savings

provision, which states that it is to be interpreted only as broadly as

allowed by applicable law.  As stated above, such a provision ensures that

both GPLv2~\S12, and the entire GPL, is enforceable in any jurisdiction,

regardless of any particular law regarding the permissibility of limiting

liability.

So end the terms and conditions of the GNU General Public License.

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

\chapter{GPL Version 3}

\label{GPLv3}

This chapter discusses the text of GPLv3.  Much of this material herein

includes text that was adapted (with permission) from text that FSF

originally published as part of the so-called ``rationale documents'' for the

various discussion drafts of GPLv3.

The FSF ran a somewhat public process to develop GPLv3, and it was the first

attempt of its kind to develop a Free Software license this way.  Ultimately,

RMS was the primary author of GPLv3, but he listened to feedback from all

sorts of individuals and even for-profit companies.  Nevertheless, in

attempting to understand GPLv3 after the fact, the materials available from

the GPLv3 process have a somewhat ``drinking from the firehose'' effect.

This chapter seeks to explain GPLv3 to newcomers, who perhaps are familiar

with GPLv2 and who did not participate in the GPLv3 process.

Those who wish to drink from the firehose and take a diachronic approach to

GPLv3 study by reading the step-by-step public drafting process of the GPLv3 (which

occurred from Monday 16 January 2006 through Monday 19 November 2007) should

visit \url{http://gplv3.fsf.org/}.

\section{Understanding GPLv3 As An Upgraded GPLv2}

Ultimately, GPLv2 and GPLv3 co-exist as active licenses in regular use.  As

discussed in Chapter~\ref{tale-of-two-copylefts}, GPLv1 was never regularly

used alongside GPLv2.  However, given GPLv2's widespread popularity and

existing longevity by the time GPLv3 was published, it is not surprising that

some licensors still prefer GPLv2-only or GPLv2-or-later.  GPLv3 gained major

adoption by many projects, old and new, but many projects have not upgraded

due to (in some cases) mere laziness and (in other cases) policy preference

for some of GPLv2's terms and/or policy opposition to GPLv3's terms.

Given this ``two GPLs world'' is reality, it makes sense to consider GPLv3 in

terms of how it differs from GPLv2.  Also, most of the best GPL experts in

the world must deal regularly with both licenses, and admittedly have decades

of experience with GPLv2 while the most experience with GPLv3 that's possible

is by default less than a decade.  These two factors usually cause even new

students of GPL to start with GPLv2 and move on to GPLv3, and this tutorial

follows that pattern.

Overall, the changes made in GPLv3 admittedly \textit{increased} the

complexity of the license.  The FSF stated at the start of the GPLv3 process

that they would have liked to oblige those who have asked for a simpler and

shorter GPL\@.  Ultimately, the FSF gave priority to making GPLv3 a better

copyleft license in the spirit of past GPL's.  Obsession for concision should

policy requires each such patent holder to provide appropriate levels of

patent assurance to users, according to the nature of the patent holder's

relationship to the program.

\subsection{The Contributor's Explicit Patent License}

Specifically, the ideal might have been for GPLv3 to feature a patent license

grant triggered by all acts of distribution of GPLv3-covered works.  The FSF

considered it during the GPLv3 drafting process, but many patent-holding

companies objected to this policy.  They have made two objections: (1) the

far-reaching impact of the patent license grant on the patent holder is

disproportionate to the act of merely distributing code without modification

or transformation, and (2) it is unreasonable to expect an owner of vast

patent assets to exercise requisite diligence in reviewing all the

GPL-covered software that it provides to others.  Some expressed particular

concern about the consequences of ``inadvertent'' distribution.

The argument that the impact of the patent license grant would be

``disproportionate'',  that is to say unfair, is not valid. Since

software patents are weapons that no one should have, and using them for

aggression against free software developers is an egregious act (thus

preventing that act cannot be unfair). 

However, the second argument seems valid in a practical sense.  A

typical GNU/Linux distribution includes thousands of programs.  It would

be quite difficult for a re-distributor with a large patent portfolio to

review all those programs against that portfolio every time it receives

and passes on a new version of the distribution.  Moreover, this question

raises a strategic issue. If the GPLv3 patent license requirements

convince patent-holding companies to remain outside the distribution

path of all GPL-covered software, then these requirements, no matter how

strong, will cover few patents. 

GPLv3 therefore makes a partial concession

which would lead these companies to feel secure in doing the

distribution themselves. GPLv3~\S11

applies only to those distributors that have

modified the program.  The other changes we have made in sections 10 and

11 provide strengthened defenses against patent assertion and compensate

partly for this concession. 

Therefore, GPLv3~\S11 introduces the terms ``contributor'', ``contributor version'', and

``essential patent claims'', which are

used in the GPLv3~\S11\P3.   Viewed from the perspective of a recipient of the

Program, contributors include all the copyright holders for the Program,

other than copyright holders of material originally licensed under non-GPL

terms and later incorporated into a GPL-covered work.  The contributors are

therefore the initial GPLv3 licensors of the Program and all subsequent

upstream licensors who convey, under the terms of GPLv3~\S5, modified covered

works.

Thus, the ``contributor version'' includes the material the contributor has copied from the

upstream version that the contributor has modified.  GPLv3~\S11\P3

 does not apply to those that redistribute the program

without change.\footnote{An implied patent license from the distributor,

however, often arises.  See \S~\ref{gpl-implied-patent-grant} in this tutorial}

In other words, the ``contributor version'' includes not just

the material added or altered by the contributor, but also the pre-existing

material the contributor copied from the upstream version and retained in the

modified version.  (GPLv3's usage of ``contributor'' and ``contribution'' should

not be confused with the various other ways in which those terms are used in

certain other free software licenses\footnote{Cf., e.g., Apache License,

  version 2.0, section 1; Eclipse Public License, version 1.0, section 1;

  Mozilla Public License, version 1.1, section 1.1.}.)

Some details of the ``essential patent claims'' definition deserve special

mention.  ``Essential patent claims'', for a given party, are a subset of the

claims ``owned or controlled'' by the party.  They do include sublicensable

claims that have been licensed to the contributor by a third

party.\footnote{This issue is typically handled in other software freedom

  licenses having patent licensing provisions by use of the unhelpful term

  ``licensable,'' which is either left undefined or is given an ambiguous

  definition.}  Most commercial patent license agreements that permit

sublicensing do so under restrictive terms that are inconsistent with the

requirements of the GPL\@.  For example, some patent licenses allow the

patent licensee to sublicense but require collection of royalties from any

sublicensees.  The patent licensee could not distribute a GPL-covered program

and grant the recipient a patent sublicense for the program without violating

section 12 of GPLv3.\footnote{GPLv3 also provides an example in section 12

  that makes this point clear.}  In rare cases, however, a conveying party

can freely grant patent sublicenses to downstream recipients without

violating the GPL\@.

Additionally, ``essential patent claims'' are those patents ``that would be

infringed by some manner, permitted by this License, of making, using, or

selling the work''.  This intends to make clear that a patent claim is

``essential'' if some mode of usage would infringe that claim, even if there

are other modes of usage that would not infringe.

Finally, ``essential patent claims \ldots do not include

claims that would be infringed only as a consequence of further

modification of the work.''  The set of essential patent

claims licensed  is fixed by the

particular version of the work that was contributed.  The claim set

cannot expand as a work is further modified downstream.  (If it could,

then any software patent claim would be included, since any software

patent claim can be infringed by some further modification of the

work.)\footnote{However, ``the work'' should not be understood to be

restricted to a particular mechanical affixation of, or medium for

distributing, a program, where the same program might be provided in

other forms or in other ways that may be captured by other patent claims

held by the contributor.}

\medskip

Ideally, this contributor patent policy will result in fairly frequent licensing of patent

claims by contributors.  A contributor is charged with awareness of the fact

that it has modified a work and provided it to others; no act of contribution

should be treated as inadvertent.  GPLv3's rule also requires no more work, for a

contributor, than the weaker rule proposed by the patent holders.  Under

their rule, the contributor must always compare the entire work against its

patent portfolio to determine whether the combination of the modifications

with the remainder of the work cause it to read on any of the contributor's

patent claims.

\subsection{Conveyors' Patent Licensing}

The remaining patent licensing in GPLv3 deals with patent licenses that are

granted by conveyance.  The licensing is not as complete or far reaching as

the contributor patent licenses discussed in the preceding section.

The term ``patent license,'' as used in GPLv3~\S11\P4--6, is not meant to be

confined to agreements formally identified or classified as patent licenses.

GPLv3~\S11\P3  makes this clear by defining ``patent

license,'' for purposes of the subsequent three paragraphs, as ``any express

agreement or commitment, however denominated, not to enforce a patent

(such as an express permission to practice a patent or covenant not to

sue for patent infringement)''

% The definition does not include patent licenses that arise by

% implication or operation of law, because the third through fifth paragraphs

% of section 11 are specifically concerned with explicit promises that purport

% to be legally enforceable.

GPLv3~\S11\P5 is commonly called GPLv3's downstream shielding provision.  It

responds particularly to the problem of exclusive deals between patent

holders and distributors, which threaten to distort the free software

distribution system in a manner adverse to developers and users.  The

fundamental idea is to make a trade-off between assuring a patent license for

downstream and making  (possibly patent-encumbered) CCS publicly available.

Simply put, in nearly all cases in which the ``knowingly relying'' test is

met, the patent license will indeed not be sublicensable or generally

available to all on free terms.  If, on the other hand, the patent license is

generally available under terms consistent with the requirements of the GPL,

the distributor is automatically in compliance, because the patent license

has already been extended to all downstream recipients.  Finally, if the

patent license is sublicensable on GPL-consistent terms, the distributor may

choose to grant sublicenses to downstream recipients instead of causing the

CCS to be publicly available.  (In such a case, if the distributor is also a

contributor, it will already have granted a patent sublicense anyway, and so

it need not do anything further to comply with the third paragraph.)

Admittedly, public disclosure of CCS is not necessarily required by other

sections of the GPL, and the FSF in drafting GPLv3 did not necessarily wish

to impose a general requirement to make source code available to all, which

has never been a GPL condition.  However, many vendors who produce products

that include copylefted software, and who are most likely to be affected by the

downstream shielding provision, lobbied for the addition of the source code

availability option, so it remains.

Meanwhile, two specific alternatives to the source code availability option

are also available. The distributor may comply by disclaiming the patent

license it has been granted for the conveyed work, or by arranging to extend

the patent license to downstream recipients\footnote{The latter option, if

  chosen, must be done ``in a manner consistent with the requirements of this

  License''; for example, it is unavailable if extension of the patent

  license would result in a violation of GPLv3~\S 12.}.  The GPL is intended

to permit private distribution as well as public distribution, and the

addition of these options ensures that this remains the case, even though it

remains likely that distributors in this situation will usually choose the

source code availability option.

Note that GPLv3~\S11\P5 is activated only if the CCS is not already otherwise

publicly available.  (Most often it will, in fact, already be available on

some network server operated by a third party.)  Even if it is not already

available, the option to ``cause the Corresponding Source to be so

available'' can then be satisfied by verifying that a third party has acted

to make it available.  That is to say, the affected distributor need not

itself host the CCS to take advantage of the source code availability option.

This subtlety may help the distributor avoid certain peculiar assumptions of

liability.

Note that GPLv3~\S11\P6--7 are designed to stop distributors from colluding with

third parties to offer selective patent protection.  GPLv3 is designed to

ensure that all users receive the same rights; arrangements that circumvent

this make a mockery of free software, and we must do everything in our power

to stop them.

First, GPLv3~\S11\P6 states that any license that protects some recipients of

GPL'd software must be extended to all recipients of the software.  

If conveyors arrange to provide patent

protection to some of the people who get the software from you, that

protection is automatically extended to everyone who receives the software,

no matter how they get it. 

Second, GPLv3~\S11\P7

prohibit anyone who made such an agreement from distributing software

released under GPLv3.    Conveyors are prohibited from

distributing software under GPLv3 if the conveyor makes an agreement of that

nature in the future.

The date in GPLv3~\S11\P7 likely seems arbitrary to those who did not follow

the GPLv3 drafting process.  This issue was hotly debated during the drafting of

GPLv3, but ultimately one specific deal of this type --- a deal between Microsoft

and Novell for Microsoft to provide so-called ``coupons'' to Microsoft customers to redeem

for copies of Novell's GNU/Linux distribution with a Microsoft patent license -- was

designed to be excluded.

The main reason for this was a tactical decision by the FSF.  FSF believed they can do more to

protect the community by allowing Novell to use software under GPLv3

than by forbidding it to do so.  This is because of

paragraph 6 of section 11 (corresponding to paragraph 4 in Draft 3).

It will apply, under the Microsoft/Novell deal, because of the coupons

that Microsoft has acquired that essentially commit it to participate

in the distribution of the Novell SLES GNU/Linux system.

The FSF also gave a secondary reason:  to avoid affecting other kinds of agreements for

other kinds of activities.  While GPLv3 sought to 

distinguish pernicious deals of the Microsoft/Novell type from

business conduct that is not particularly harmful, the FSF also did not

assume success in that drafting, and thus there remained some risk that other

unchangeable past agreements could fall within the  scope of GPLv3~\S11\P7.

In future deals, distributors engaging in ordinary business practices

can structure the agreements so that they do not fall under GPLv3~\S11\P7.

\section{GPLv3~\S12: Familiar as GPLv2~\S7}

GPLv2~\S12 remains almost completely unchanged from the text that appears in

GPLv2~\S7.  This is an important provision that ensures a catch-all to ensure

that nothing ``surprising'' interferes with the continued conveyance safely

under copyleft.

The wording in the first sentence of GPLv3~\S12 has been revised slightly to

clarify that an agreement -- such as a litigation settlement agreement or a

patent license agreement -- is one of the ways in which conditions may be

``imposed'' on a GPL licensee that may contradict the conditions of the GPL,

but which do not excuse the licensee from compliance with those conditions.

This change codifies the historical interpretation of GPLv2.

GPLv3 removed the limited severability clause of GPLv2~\S7 as a

matter of tactical judgment, believing that this is the best way to ensure

that all provisions of the GPL will be upheld in court. GPLv3 also removed

the final sentence of GPLv2 section 7, which the FSF consider to be unnecessary.

\section{GPLv3~\S13: The Great Affero Compromise}

The Affero GPL was written with the expectation that its

additional requirement would be incorporated into the terms of GPLv3

itself.  Many software freedom advocates, including some authors of this

tutorial, advocated heavily for that, and fully expected it to happen.

The FSF, however, chose not to include the Affero clause in GPLv3, due to

what it called  ``irreconcilable views from

different parts of the community''.  Many

commercial users of Free Software were opposed to the inclusion of a