If I were to make deep modifications to the Linux kernel, virtually make a 'new' kernel in a way, for my project, which is building my own operating system, (yes, I know, a lot of work, but hey, I'm quite a dedicated guy when it comes it working on projects of any kind.) and if I don't want the source disclosed, is this even possible with Linux's license?
Would I have to include the 'new' kernel's source code if I decide or even manage to release the operating system? What about if it's closed source, but not paid-for software?
What if you change it or add to it, but you don't want to make the code you added open source? Must I also open source that code I made that I would wish to keep closed?