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Institute for Legal Questions on Free and Open Source Software

III. The GNU General Public License (GPL), Version 2

What kind of source code do I have to publish under the GNU GPL?

This FAQ originates from and is published with consent of Harald Welte. It contains some more detailed information on the requirements and best current practise of providing corresponding source code for GPL licensed executable code. It was compiled as a result of the numerous shortcomings and mistakes of more than sixty successful GPL enforcements.


The GNU GPL demands that as soon as you distribute GPL licensed software in executable format you make available the "complete corresponding source code". The GNU GPL also contains a definition of this term: » Weiter

When does independently developed software have to be licensed under the GPL?

Whether code distributed together with GPL software (especially independently developed software) has to be subject to the GPL depends on how the LGPL software and independent code interact.  sec. 2 GPLv2 describes the necessary criteria.  The basic rule is found under sec. 2b) GPLv2:

"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 that license." » Weiter

What are the obligations involved in the internal use of software licensed under GPLv2?

If software is merely used or run, there are no associated obligations (see sec. 0 GPLv2). The right to run the software is not expressly granted by the GPLv2. This is also not necessary. The legal acquiring party is already generally entitled to do this by law: sec. 69d Para. 1 UrhG (German Copyright Law) stipulates that, in the absence of any special contractual provisions governing this matter, the actions required to properly use the computer program do not require the approval of the right holder. The actions required to run the software are therefore already legally permissible.  This legal regulation ensures that no copies of the program in economic circulation with the understanding of the rights holder may be used without entitlement.  The provision ensures that each entitled user can exploit the provided software in the provided manner.  The fact that GPLv2 does not restrict these legal rights is clearly stated in sec. 0 Para. 2 GPL: » Weiter

What obligations are involved in distributing changed versions of software licensed under the GPLv2?

a)    Licensing your own software under GPLv2 (Copyleft)
If a program licensed under GPLv2 was changed enough to yield a "derivative work" in accordance with sec. 2 GPLv2   (→ When does independently developed software have to be licensed under the GPL?), the changed software in its entirety may only be given to third parties under the license conditions of GPLv2 (see sec. 2 GPLv2).
b)    Notification of change
Changed software files must contain a reference that changes were made, as well as the date of such changes (see sec. 2 GPLv2).
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What obligations are involved in distributing software licensed under the GPLv2?

The licensee has the following obligations when distributing software under the GPLv2:
a) Delivery of the license text
According to sec. 1 GPLv2, a copy of the license text must be provided with the copy of the program. This can be a physical copy printed on paper, or a nonphysical copy in the form of a corresponding text file. This duty ensures that each acquiring party can learn about how to acquire rights from GPL and will receive an offer to conclude a license agreement.
b) Copyright sign
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What rights can be acquired by the GPL?

Like all open source licenses, the GPLv2 grants the right to copy the program, modify it, and distribute it in an unchanged or changed version (→ How can I use open source software?). This includes both the online offer and the offline distribution. In terms of copyright, this involves the granting of simple (“non-exclusive”) rights of use unrestricted by time or place.
Next FAQ: What obligations are involved in distributing software licensed under the GPLv2?

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What is the GPL?

The GNU General Public License (GPL) is the most well-known license for "free software."  Version 1 of this license was used for the first time in 1989. The second version of the GPL (→ GNU General Public License, Version 2) appeared in 1991, and the new Version 3 (→ GNU General Public License, Version 3) appeared in 2007. The GPLv2 is essentially the work of Richard Stallman, the founder of the GNU project. Large sections of the Linux kernel as well as numerous other successful Open Source programs are licensed under the GPLv2.
  » Weiter

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