Microsoft, at its recent BUILD event, has announced that Windows Subsystem for Linux (WSL) is now open source after almost a decade of development.
The Microsoft team has closed issue #1 in its GitHub issue tracker. What was the issue? "Will this (WSL) be Open Source?" – an issue that has been open since April 6, 2016. WSL is now open source, meaning that anyone can download the WSL code, build it from source, and then add features and fixes before pushing the code for review and possible integration into the main project.
WSL was first announced at BUILD back in 2016, so it is fitting that the news of WSL going open source was announced at the recent BUILD event taking place in Seattle.
"Windows Subsystem for Linux (WSL) is a powerful way for you to run your Linux command-line tools, utilities and applications, all unmodified and directly on Windows without the overhead of a traditional virtual machine or dual boot setup." - WSL GitHub readme.
WSL is a virtualization setup for Windows users to run Linux distributions inside the Windows host OS with integration between the guest Linux OS and the Windows host.
WSL 1 was initially based on a pico process provider, lxcore.sys. This provided Windows with a native means to run ELF executables, and Linux syscalls all inside the Windows kernel. In 2019, in an effort to provide "optimal compatibility with native Linux", a Linux kernel, provided and maintained by Microsoft, was introduced.
WSL gained more features, including GPU support, graphical applications via wslg (which is already open source) and support for systemd (a system and service manager for many Linux distros).
In 2021, Microsoft separated WSL from the Windows codebase as a means to move faster and to keep up with the community requests. The new standalone WSL was available via the Microsoft Store, starting with version 0.47.1. At that time, only Windows 11 was supported, and only recommended for users eager to run bleeding edge software. With WSL 2, major improvements were introduced, such as mirrored networking, DNS tunnelling, firewall support, and proxy support.
In 2025, WSL improved how Linux distros were installed, enabling local images to be used away from the store.
"WSL could never have been what it is today without its community. Even without access to WSL’s source code, people have been able to make major contributions that lead to what WSL is now," says Senior Software Engineer Pierre Boulay in the blog post.
