Windows 10 to Include a Linux Kernel for WSL

Posted on May 6, 2019 by Paul Thurrott in Windows 10 with 62 Comments

Future versions of Windows 10 will ship with a real Linux kernel that offers dramatically better WSL performance.

“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),” Microsoft’s Jack Hammons announced. “This marks the first time that the Linux kernel will be included as a component in Windows. This is an exciting day for all of us on the Linux team at Microsoft and we are thrilled to be able to tell you a little bit about it.”

The inclusion of a Linux kernel in Windows 10 came as a bit of a surprise, even for those of us, like me, who had been pre-briefed by Microsoft about what to expect at Build this year. Consider the following description of WSL 2, which Microsoft provided to the press ahead of the show:

“The next generation of the Windows Subsystem for Linux (WSL) will offer technology built for Microsoft Azure to the Windows Desktop to address the top customer requests for improved performance and compatibility … developers will experience up to twice as much speed for file-system heavy operations, such as Node Package Manager install.”

That doesn’t say anything about a Linux kernel, and current versions of WSL utilize an emulator, not a real Linux kernel. And based on that documentation, I wrote what I wrote earlier about this and other changes that will impact Windows 10 this year.

But a Microsoft blog post that includes a reference to this new feature explicitly mentions the new kernel, and the press didn’t see it until this morning, like everyone else.

“Windows Subsystem for Linux 2 (WSL 2) is the next version of WSL and is based on a Linux 4.19 kernel shipping in Windows … WSL 2 also improves filesystem I/O performance [and] Linux compatibility,” the post notes.

Hammons’ post goes into greater detail about the kernel. It will initially be based on version Linux 4.19, the latest long-term stable release of the platform, and it will be updated to each new long-term stable release to ensure that it’s always up-to-date. Microsoft says it is a “drop-in replacement” for the current emulator. It will also be fully open source.

“This is the culmination of years of effort from the Linux Systems Group as well as multiple other teams across Microsoft,” Hammons notes. “We are excited to be able to share the result and look forward to the new and interesting ways in which you will use WSL.”

It’s a brave new world, people. This is also probably one of the reasons that Microsoft hasn’t begun testing Windows 10 19H2 yet: This will likely be where WSL 2 is first tested and then released, and I suspect that Microsoft wanted to keep news of the Linux kernel a secret until Build.

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