Microsoft open sources Windows Subsystem for Linux - well, most of it

Microsoft has open-sourced the Windows Subsystem for Linux, years after the platform's debut.

The Windows Subsystem for Linux was first announced in 2016 and shipped with the Windows 10 Anniversary Update that year. It was based on a pico process provider, lxcore.sys, which enabled Windows to run ELF executables natively via a compatibility layer.

It was (and is) a helpful tool. However, there were compatibility issues that could only be overcome by implementing a real Linux kernel and running everything in a managed virtual machine. An update, dubbed Windows Subsystem for Linux 2, did just that, and was rolled out to testers in 2019. In 2021, Microsoft pulled the code from Windows. After all, having things tied to the Windows release cadence sat at odds with the pace of updates in the Linux world.

By 2024 and the debut of Windows 11 24H2, Microsoft said it had finished transitioning users to its new WSL package, "and away from the WSL component that shipped with Windows."

Components of WSL2 have always been open source due to its use of a Linux kernel. However, according to Microsoft, almost everything closed is now open. "That means that the code that powers WSL is now available on GitHub at Microsoft/WSL and open sourced to the community!" the company said.

"You can download WSL and build it from source, add new fixes and features, and participate in WSL's active development."

For anyone hoping that the decision might mean access to the Windows kernel is on the cards, sorry - lxcore.sys, the kernel-side driver that powers WSL1, is still considered part of the Windows images, and "not open sourced at this time."

The same applies to 9rdr.sys and p9np.dll, which run the \\wsl.localhost file system redirection (from Windows to Linux).

Although Microsoft said "WSL could never have been what it is today without its community," it did not provide details regarding how the project would be managed going forward. It's all well and good to welcome direct code contributions, but it's also important to know they won't disappear into a black hole if they don't fit with the direction the project is to be steered.

The Register asked Microsoft if the newly open sourced WSL would have its own steering committee or be directed by the hand of Redmond. We also wondered what this might mean for Windows Server workloads.

We will update this piece if the company responds. ®