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? [1]), 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).
c) Notification of interactive commands
If a program is interactive and contains references to the GPLv2, the exclusion of liability and/or copyright signs, these references also must be in the changed program (see sec. 2 GPLv2).
Note
This FAQ is based on the FAQs of the commentary “Die GPL kommentiert und erklaert” [Discussions and explanations of the GPL] published by ifrOSS at O’Reilly.
Next FAQ: What are the obligations involved in the internal use of software licensed under GPLv2? [2]
[3]
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