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).
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).


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.
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