Over the past few years, Microsoft has been increasingly endorsing the Linux Kernel. They allow running a stripped down version of GNU/Linux distros in Windows, and Microsoft Azure uses Linux nowadays.

What if Microsoft decides to make a version of Windows with the Linux Kernel, and continue to release it as a proprietary operating system (and only release their kernel under GPL2)?

Suppose they say, "Our kernel is free and open source (you can look up here for the source), but the rest of the OS is non-free (and we won't allow you to modify or redistribute it)". Can they legally do that?

  • That's basically how macOS works, only with a different open-source kernel.
    – jwodder
    Feb 11 '21 at 22:37

Yes, they can.

Firstly, the kernel is licensed under GPLv2 with a syscall exception, which says that the kernel's "copyright does not cover user programs that use kernel services by normal system calls - this is merely considered normal use of the kernel, and does not fall under the heading of "derived work"". So Microsoft could certainly found a new proprietary OS on the Linux kernel.

Secondly, this is already routinely done on Android phones: the kernel is Linux (or, at the very least, a derivative of the Linux kernel, and thus must also be covered by GPLv2) but user-space is packed with proprietary programs running on a partially-proprietary OS (think of all the Google-specific bits).

I don't think there's chance in a million of this happening, but I can't see any licensing bar to it.

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