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Comment by dramaticus3 | Hacker News Reader

> Fortunately, thanks to the GPLv2, all the significant changes come back to the mainstream kernel.

How exactly, does that work ?

This is a valid questions, because iirc, as long as these companies don't distribute their linux fork outside of their company, they do not need to release the source. GPL takes effect when you distribute binaries, not when you create them.

Exactly. I guess the license doesn't really matter a lot in this case, as long as it's some sort of Open Source license. The benefit the companies have by getting their patches merged back in is that they don't necessarily have to maintain the patches themselves anymore. The GPL, however, should not have any effect on that, as long as the work is used internally only.

If you copy or distribute the derivate work in either object code or executable form, you are obliged to make the source available.

Arguably anyone who has a phone, has had a copy in executable form distributed to them, and can ask for the source.

He was talking about Google's private fork of Linux for their servers to run Google search.

He was talking about companies in general tweaking linux for their particular uses.

Indeed, if you focus on the preceding bit about Google's in-house linux for their own servers, then there would be no distribution and arguably GPL2 could not force those modifications to be made public.

But I would imagine that he's probably quite versed in GPL2 and knows this -- so since he brought it up specifically, it suggests he was probably thinking at that point more about cases where distribution does happen (e.g. Android, embedded etc).

Perhaps he considers it a 'significant change' primarily if there's some sort of distribution ;)

It used to be the case that licenses required you to submit your modifications back to the source. Lucent's first stab at opening Plan 9 From Bell Labs back in '99 had such a clause.

Derivative works of the kernel must also be licensed under the GPL, meaning their source code must be available. So, if the Linux developers like the changes someone else has made, they can merge them in.

No. GPL doesn't mean that derivative works source needs to be available. Thus Google may very well have modifications which are never made public.

The source must be available to those who have access to the program. If Google ever distributed those modifications, they would have to distribute the source as well.

That's the big if. Especially when the paragraph was discussing Googles performance tweaks to their in-house kernel used in their servers.

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