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Believe it or not, Jack Hammons, Microsoft Program Manager, recently wrote, "Beginning with Windows Insiders builds this Summer, we will include an in-house custom-built Linux kernel to underpin the newest version of the Windows Subsystem for Linux (WSL)." Yes, that's right, Microsoft is releasing its own Linux kernel.

I don't know if Hell is freezing over, but it is getting a mite chilly down there.

A few months ago I said, Microsoft might release its own MS-Linux or Lindows. Now, Microsoft is not doing that. Not yet anyway. But this is another step in that direction.

As Hammons wrote, "This marks the first time that the Linux kernel will be included as a component in Windows."

It will not be running under Windows per se. Instead it provides a Microsoft homebrew kernel for WSL. This includes Microsoft patches so WSL will work better with Windows. "These patches tune the resulting binary for use in WSL2 by improving launch times, reducing the memory footprint and curating a minimal set of supported devices. The result is a small, lightweight kernel that is purpose built for WSL2 to be a drop-in replacement" for WSL's original emulation architecture.

This fully open-source Linux "will initially be based on version 4.19, the latest long-term stable release of Linux. The kernel will be rebased at the designation of new long-term stable releases to ensure that the WSL kernel always has the latest Linux goodness."

All WSL's changes will go upstream to the main Linux kernel. But, "during development it is necessary to work with local patches that enable new features or address issues in upstream. In these cases, we either create, or find patches that fulfill our product requirements and then work with the community to get that code integrated as soon as possible."

Before you get up in arms, this kind of thing happens all the time in Linux circles. Features often first appear in Linux distros from Red Hat, SUSE, or Ubuntu before being merged into mainline Linux.

The only potential problem is if Microsoft follows Android's early missteps of building Linux distributions that don't work and play well with mainline Linux. The Android vendors eventually got back into step with Linux. I can't see Microsoft making that blunder.

WSL2 is here, you'll still be able to run your Linux distro of choice on top of Microsoft's Linux kernel. This includes Debian GNU/Linux, Kali Linux, OpenSUSE, and SUSE Linux Enterprise Server (SLES), and Ubuntu.

That's because Microsoft is just building a Linux kernel designed to make the most of its Windows environment. It's not even the first to optimize a Linux kernel for Windows. That honor goes to Pengwin.

Microsoft will release the WSL kernel source as links to a set of patches to the long-term stable Linux source. When WSL2 is released in Windows Insider builds, Microsoft will provide instructions for creating your own WSL kernel on GitHub. This GitHub repository is not available yet.

But, with Microsoft looking for Linux software engineers today, you may be able to help put the code out tomorrow.

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