of legal issues to consider, the more mundane ways to create a new work

covered by GPL are much more common.  For example, copyright statutes

generally require permission from the copyright holder to grant explicit

permission to modify a work in any manner.  As discussed in the next chapter,

the GPL {\em does} grants such permission, but requires the modified work must

also be licensed under the terms of the GPL (and only GPL:

see\S~\label{GPLv2s6} in this tutorial).  Determining whether software was

modified is a substantially easier analysis than the derivative work

discussions and considerations in this chapter.

The question of derivative works, when and how they are made, is undoubtedly

an essential discussion in the interpretation and consideration of copyleft.

That is why this chapter was included in this tutorial.  However, as we

return from this digression and resume discussion of the detailed text of the

GPLv2, we must gain a sense of perspective: most GPL questions center around

questions of modification and distribution, not preparation of derivative

works.  Derivative work preparation is ultimately a small subset of the types

of modified versions of the software a developer might create, thus, while an

excessive focus on derivative works indulges us in the more exciting areas of

copyleft, we must keep a sense of perspective regarding their relative

importance.

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

\chapter{Modified Source and Binary Distribution}

\label{source-and-binary}

In this chapter, we discuss the two core sections that define the rights

and obligations for those who modify, improve, and/or redistribute GPL'd

software. These sections, GPLv2~\S\S2--3, define the central core rights and

requirements of GPLv2\@.

\section{GPLv2~\S2: Share and Share Alike}

\label{GPLv2s2}

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

freedom upon redistribution.  GPLv2~\S2 is the only place in GPLv2

that governs the modification controls of copyright law.  If users

distribute modified versions a GPLv2'd program, they must follow the terms of GPLv2~\S2 in making

those changes.  Thus, this sections ensures that the body of GPL'd software, as it

continues and develops, remains Free as in freedom.

To achieve that goal, GPLv2~\S2 first sets forth that the rights of

redistribution of modified versions are the same as those for verbatim

copying, as presented in GPLv2~\S1.  Therefore, the details of charging money,

keeping copyright notices intact, and other GPLv2~\S1 provisions are intact

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

The first (GPLv2~\S2(a)) requires that modified files carry ``prominent

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

changes. This section does not prescribe some specific way of

marking changes nor does it control the process of how changes are made.

Primarily, GPLv2~\S2(a) seeks to ensure that those receiving modified

versions know the history of changes to the software.  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 about the

historical context of the software version they use, so that they can

make proper support choices.  Finally, GPLv2~\S2(a) serves an academic

purpose --- ensuring that future developers can use a diachronic

approach to understand the software.

GPLv2~\S2(c), a relatively simple section, requires that any program which

(before modification) ``normally reads commands interactively when run'' and

displays or prints legal information also display all copyright notices,

warranty disclaimer, modification indications and a pointer to the license,

even in modified versions.  The requirement is relatively simple, and relates

to an important policy goal of copyleft: downstream users should be informed

of their rights.  Its implications and details are straightforward and

simple.

Meanwhile, GPLv2~\S2(b) requires careful and extensive study.  Its four short lines embody

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

considered by some to be the most worthy of careful scrutiny because

GPLv2~\S2(b), and they

can be a source of great confusion when not properly understood.

In considering GPLv2~\S2(b), first note the qualifier: it \textit{only} applies to

derivative, combined and/or modified works that ``you distribute or publish''.  Despite years of

education efforts on this matter, many still believe that modifiers

of GPL'd software \textit{must} publish or otherwise

share their changes.  On the contrary, GPLv2~\S2(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{Most Free Software enthusiasts believe there is a {\bf

    moral} obligation to redistribute changes that are generally useful,

  and they often encourage 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 GPLv2~\S0, in the

following text:

\begin{quote}

``...that in whole or part contains or is derived from the Program or any part thereof.''

\end{quote}

Again, the GPL relies here on copyright law.

If, under copyright law, the modified version ``contains or is

derived from'' the GPL'd software, then the requirements of GPLv2~\S2(b)

apply.  The GPL invokes its control as a copyright license over the

modification of the work in combination with its control over distribution

of the work.

The final clause of GPLv2~\S2(b) describes what the licensee must do if she

distributes or publishes a modified version of the work --- namely, the following:

\begin{quote}

[The work must] be licensed as a whole at no charge to all third parties

under the terms of this License.

\end{quote}

That is probably the most tightly-packed phrase in all of the GPL\@.

Consider each subpart carefully.

The work ``as a whole'' is what is to be licensed. This is an important

point that GPLv2~\S2 spends an entire paragraph explaining; thus this phrase is

worthy of a lengthy discussion here.  As a programmer modifies a software

program, she generates new copyrighted material --- fixing expressions of

ideas into the tangible medium of electronic file storage.  That

programmer is indeed the copyright holder of those new changes.  However,

those changes are part and parcel to the original work distributed to