Microsoft has announced something interesting for Windows 10 users that could mean buyers no longer need to decide between a Windows machine and a dedicated Linux machine like Dell's new Ubuntu workstations unveiled a few days ago. Microsoft has announced that starting with Windows 10 Insider Preview builds this summer it will include an in-house custom-built Linux kernel in the OS.
That kernel will be used to underpin the newest version of the Windows Subsystem for Linux or WSL. This is the first time that a Linux kernel will be included as a component in Windows. Microsoft's Jack Hammons, program manager for Linux systems group, wrote that the term "Linux" is often used to refer to both the Linux kernel and the GNU userspace. Hammons notes that as with WSL1 and WSL2, Microsft will provide no userspace binaries with the new integrated Linux kernel.
The Microsoft kernel will interface with userspace selected by the user normally added as an installation via the Windows Store. The userspace can also be sideloaded via a custom distribution package. The exception to that rule is a small init script injected to bootstrap the startup process to form the connections between Windows and Linux. Microsoft's kernel will be based on version 4.19, which Hammons says it the latest long-term stable release of Linux.
He also notes that the kernel will be rebased at the designation of new long-term stable releases to be sure WSL is always on the latest Linux version. Microsoft adds that in addition to the LTS source from Kernel.org, several local patches are being applied to tune the binary for use in WSL2 by improving launch times, reducing memory footprint, and curating a minimal set of supported devices. Microsoft says that all changes go upstream, but it is possible that some patches with new features might only be included in future versions of the kernel and not be back-ported to the current LTS.
The kernel Microsoft uses leverages its CI/CD system and is serviced through Windows Update in an operation transparent to the user. That means the kernel is up to date with new fixes and features in the latest stable branch of Linux. The kernel provided for WSL2 is fully open source. Instructions for creating a custom WSL kernel will be made available on Github when WSL2 is released in Insider Preview builds.