Linux has already been re-licensed: when Linus removed the "or later" language.
It's sufficient to post a public notice that you're going to make the change, and wait an appropriate amount of time for any copyright holders to object. There's no need to contact, individually, every possible copyright holder.
Posted Aug 20, 2009 14:21 UTC (Thu) by mjg59 (subscriber, #23239)
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That's not re-licensing - it's choosing to only distribute further versions under GPLv2, as is expressly permitted in the "or later" boilerplate. Anyone can take any GPL code with that language and redistribute it without.
Difficult, but first there has to be a will
Posted Aug 20, 2009 15:47 UTC (Thu) by fb (subscriber, #53265)
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Linus never removed the "or later" language, as he never had the "or later" thing in his code. The license in the kernel has always been a verbatim copy of GPLv2.
What happened is that the wording "only" was added at some point for clarification.