Servicing the Windows Subsystem for Linux (WSL) 2 Linux kernel

Craig Loewen

Note: This blog post is co-authored by the awesome WSL dev Pierre Boulay. Thanks Pierre! 😊

We’ve just shipped the 5.10.16.3 WSL 2 Linux kernel version to Windows Insiders which brings exciting new changes: Support for the LUKS disk encryption, and some long-awaited bug fixes. We’d like to seize this opportunity to highlight these improvements and show you how these changes land on your Windows machine no matter your Windows version.

New feature addition: Support for LUKS disk encryption

This kernel update adds support for LUKS disk format. Such disks can now we accessed using wsl –mount.

LUKS disks can be mounted through the following steps: (Refer to distro specific instructions to install cryptsetup if needed).

$ wsl --mount [disk-id] --bare
$ wsl cryptsetup luksOpen /dev/sdX my-device # Replace /dev/sdX with the block device path in WSL.
$ wsl mkdir /mnt/wsl/my-mountpoint
$ wsl mount /dev/mapper/my-device /mnt/wsl/my-mountpoint

The disk content can then be accessed by navigating to \\wsl$\<yourDistroName>\mnt\wsl (Replace with the name of your distro, any disto works). Please check the wsl –mount docs page for full instructions on how to mount a disk in WSL.

Bug fix: Clock sync

This new kernel version also contains a bug fix for a clock sync issue (Github Issue #5324). This issue causes the clock inside of your WSL 2 instances to be different than the actual time on your host machine. This bug was fixed entirely by changes inside of the Linux kernel itself that are present in this latest version.

Our kernel servicing process

These changes are very easy to get onto your machine, in fact it’s likely you won’t even notice that you are put onto the latest kernel version! We leverage Microsoft Update to ship this to you, and by hitting ‘Check for Updates’ in your settings, or just letting your computer update like normal, you’ll be kept up to date.

Microsoft Update delivers general updates to your operating system that don’t rely on giving a full update to your Windows build. These updates include things such as the latest virus definitions for Windows Defender, new graphics or sound card drivers, and now updates to your WSL 2 Linux kernel.

At Microsoft, the Linux Systems Group is responsible for creating the WSL 2 Linux kernel. You can read about this process at the ‘Shipping a Linux Kernel with Windows’ blog post. Once they have a kernel version ready, we test it internally to make sure it works on WSL 2 scenarios, and then ship it to Windows Insiders. The Windows Insiders audience is an invaluable group of people who use early preview versions of Windows, and so we recruit their help as well to get the first preview of new WSL 2 Linux kernels. Our release process is data driven, and once we’ve gained enough confidence on the quality of the new kernel, we expand its audience to further Windows Insider rings and then eventually to retail.

We publish our kernel version history to the Linux kernel release notes page on the WSL docs, and since the WSL 2 Linux kernel is fully open source we make sure to link to its source code as well.

Where to learn more and give feedback

For any WSL issues please file them at the WSL Github repo. If you’d like to learn more about WSL please check out the WSL docs, and if you have general questions you can follow me on Twitter @craigaloewen and WSL team members at this list. Happy coding!

Craig Loewen Senior Product Manager, Windows Developer Platform

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