The licenses for most software are designed to take away
your freedom to share and change it. By contrast, the GNU
General Public License is intended to guarantee your
freedom to share and change free software-to make sure the
software is free for all its users. This General Public
License applies to most of the Free Software Foundation’s
software and to any other program whose authors commit to
using it. (Some other Free Software Foundation software
is covered by the GNU Library General Public License
instead.) You can apply it to your programs, too.
When we speak of free software, we are referring to
freedom, not price. Our General Public Licenses are
designed to make sure that you have the freedom to
distribute copies of free software (and charge for this
service if you wish), that you receive source code or can
get it if you want it, that you can change the software or
use pieces of it in new free programs; and that you know
you can do these things.
To protect your rights, we need to make restrictions that
forbid anyone to deny you these rights or to ask you to
surrender the rights. These restrictions translate to
certain responsibilities for you if you distribute copies
of the software, or if you modify it.
For example, if you distribute copies of such a program,
whether gratis or for a fee, you must give the recipients
all the rights that you have. You must make sure that
they, too, receive or can get the source code. And you
must show them these terms so they know their rights.
We protect your rights with two steps: (1) copyright the
software, and (2) offer you this license which gives you
legal permission to copy, distribute and/or modify the
software.
Also, for each author’s protection and ours, we want to
make certain that everyone understands that there is no
warranty for this free software. If the software is
modified by someone else and passed on, we want its
recipients to know that what they have is not the
original, so that any problems introduced by others will
not reflect on the original authors’ reputations.
Finally, any free program is threatened constantly by
software patents. We wish to avoid the danger that
redistributors of a free program will individually obtain
patent licenses, in effect making the program proprietary.
To prevent this, we have made it clear that any patent
must be licensed for everyone’s free use or not licensed
at all.
The precise terms and conditions for copying, distribution
and modification follow.
GNU GENERAL PUBLIC LICENSE
TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND
MODIFICATION
0. This License applies to any program or other work which
contains a notice placed by the copyright holder saying it
may be distributed under the terms of this General Public
License. The "Program", below, refers to any such program
or work, and a "work based on the Program" means either
the Program or any derivative work under copyright law:
that is to say, a work containing the Program or a portion
of it, either verbatim or with modifications and/or
translated into another language. (Hereinafter,
translation is included without limitation in the term
"modification".) Each licensee is addressed as "you".
Activities other than copying, distribution and modification
are not covered by this License; they are outside its scope.
The act of running the Program is not restricted, and the
output from the Program is covered only if its contents
constitute a work based on the Program (independent of
having been made by running the Program). Whether that is
true depends on what the Program does.
1. You may copy and distribute verbatim copies of the
Program’s source code as you receive it, in any medium,
provided that you conspicuously and appropriately publish
on each copy an appropriate copyright notice and
disclaimer of warranty; keep intact all the notices that
refer to this License and to the absence of any warranty;
and give any other recipients of the Program a copy of
this License along with the Program.
You may charge a fee for the physical act of transferring a
copy, and you may at your option offer warranty protection
in exchange for a fee.
2. You may modify your copy or copies of the Program or
any portion of it, thus forming a work based on the
Program, and copy and distribute such modifications or
work under the terms of Section 1 above, provided that you
also meet all of these conditions:
a) You must cause the modified files to carry prominent
notices stating that you changed the files and the date
of any change.
b) You must cause any work that you distribute or
publish, that in whole or in part contains or is derived
from the Program or any part thereof, to be licensed as
a whole at no charge to all third parties under the
terms of this License.
c) If the modified program normally reads commands
interactively when run, you must cause it, when started
running for such interactive use in the most ordinary
way, to print or display an announcement including an
appropriate copyright notice and a notice that there is
no warranty (or else, saying that you provide a
warranty) and that users may redistribute the program
under these conditions, and telling the user how to view
a copy of this License. (Exception: if the Program
itself is interactive but does not normally print such
an announcement, your work based on the Program is not
required to print an announcement.)
These requirements apply to the modified work as a whole.
If identifiable sections of that work are not derived from
the Program, and can be reasonably considered independent
and separate works in themselves, then this License, and its
terms, do not apply to those sections when you distribute
them as separate works. But when you distribute the same
sections as part of a whole which is a work based on the
Program, the distribution of the whole must be on the terms
of this License, whose permissions for other licensees
extend to the entire whole, and thus to each and every part
regardless of who wrote it.
Thus, it is not the intent of this section to claim rights
or contest your rights to work written entirely by you;
rather, the intent is to exercise the right to control the
distribution of derivative or collective works based on the
Program.
In addition, mere aggregation of another work not based on
the Program with the Program (or with a work based on the
Program) on a volume of a storage or distribution medium
does not bring the other work under the scope of this
License.
3. You may copy and distribute the Program (or a work
based on it, under Section 2) in object code or executable
form under the terms of Sections 1 and 2 above provided
that you also do one of the following:
a) Accompany it with the complete corresponding
machine-readable source code, which must be distributed
under the terms of Sections 1 and 2 above on a medium
customarily used for software interchange; or,
b) Accompany it with a written offer, valid for at least
three years, to give any third party, for a charge no
more than your cost of physically performing source
distribution, a complete machine-readable copy of the
corresponding source code, to be distributed under the
terms of Sections 1 and 2 above on a medium customarily
used for software interchange; or,
c) Accompany it with the information you received as to
the offer to distribute corresponding source code.
(This alternative is allowed only for noncommercial
distribution and only if you received the program in
object code or executable form with such an offer, in
accord with Subsection b above.)
The source code for a work means the preferred form of the
work for making modifications to it. For an executable
work, complete source code means all the source code for all
modules it contains, plus any associated interface
definition files, plus the scripts used to control
compilation and installation of the executable. However, as
a special exception, the source code distributed need not
include anything that is normally distributed (in either
source or binary form) with the major components (compiler,
kernel, and so on) of the operating system on which the
executable runs, unless that component itself accompanies
the executable.
If distribution of executable or object code is made by
offering access to copy from a designated place, then
offering equivalent access to copy the source code from the
same place counts as distribution of the source code, even
though third parties are not compelled to copy the source
along with the object code.
4. You may not copy, modify, sublicense, or distribute the
Program except as expressly provided under this License.
Any attempt otherwise to copy, modify, sublicense or
distribute the Program is void, and will automatically
terminate your rights under this License. However, parties
who have received copies, or rights, from you under this
License will not have their licenses terminated so long as
such parties remain in full compliance.
5. You are not required to accept this License, since you
have not signed it. However, nothing else grants you
permission to modify or distribute the Program or its
derivative works. These actions are prohibited by law if
you do not accept this License. Therefore, by modifying
or distributing the Program (or any work based on the
Program), you indicate your acceptance of this License to
do so, and all its terms and conditions for copying,
distributing or modifying the Program or works based on
it.
6. Each time you redistribute the Program (or any work
based on the Program), the recipient automatically
receives a license from the original licensor to copy,
distribute or modify the Program subject to these terms
and conditions. You may not impose any further
restrictions on the recipients’ exercise of the rights
granted herein. You are not responsible for enforcing
compliance by third parties to this License.
7. If, as a consequence of a court judgment or allegation
of patent infringement or for any other reason (not
limited to patent issues), conditions are imposed on you
(whether by court order, agreement or otherwise) that
contradict the conditions of this License, they do not
excuse you from the conditions of this License. If you
cannot distribute so as to satisfy simultaneously your
obligations under this License and any other pertinent
obligations, then as a consequence you may not distribute
the Program at all. For example, if a patent license
would not permit royalty-free redistribution of the
Program by all those who receive copies directly or
indirectly through you, then the only way you could
satisfy both it and this License would be to refrain
entirely from distribution of the Program.
If any portion of this section is held invalid or
unenforceable under any particular circumstance, the balance
of the section is intended to apply and the section as a
whole is intended to apply in other circumstances.
It is not the purpose of this section to induce you to
infringe any patents or other property right claims or to
contest validity of any such claims; this section has the
sole purpose of protecting the integrity of the free
software distribution system, which is implemented by public
license practices. Many people have made generous
contributions to the wide range of software distributed
through that system in reliance on consistent application of
that system; it is up to the author/donor to decide if he or
she is willing to distribute software through any other
system and a licensee cannot impose that choice.
This section is intended to make thoroughly clear what is
believed to be a consequence of the rest of this License.
8. If the distribution and/or use of the Program is
restricted in certain countries either by patents or by
copyrighted interfaces, the original copyright holder who
places the Program under this License may add an explicit
geographical distribution limitation excluding those
countries, so that distribution is permitted only in or
among countries not thus excluded. In such case, this
License incorporates the limitation as if written in the
body of this License.
9. The Free Software Foundation may publish revised and/or
new versions of the General Public License from time to
time. Such new versions will be similar in spirit to the
present version, but may differ in detail to address new
problems or concerns.
Each version is given a distinguishing version number. If
the Program specifies a version number of this License which
applies to it and "any later version", you have the option
of following the terms and conditions either of that version
or of any later version published by the Free Software
Foundation. If the Program does not specify a version
number of this License, you may choose any version ever
published by the Free Software Foundation.
10. If you wish to incorporate parts of the Program into
other free programs whose distribution conditions are
different, write to the author to ask for permission. For
software which is copyrighted by the Free Software
Foundation, write to the Free Software Foundation; we
sometimes make exceptions for this. Our decision will be
guided by the two goals of preserving the free status of
all derivatives of our free software and of promoting the
sharing and reuse of software generally.