Azure Linux "Desktop": A Build 2026 mashup of wslc, WinUI Reactor, and Azure Linux 4.0
I made a thing...
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I wanted to try out some of the cool stuff that came out of Microsoft Build 2026.<br>Azure Linux "Desktop" is a small Windows app that boots a full Linux desktop in a window. It opens, starts an embedded Linux container, and a few seconds later you are looking at a themed XFCE desktop running on Azure Linux 4.0, with working audio, GPU acceleration, copy and paste, and a display that resizes with the window. No buttons, no setup wizard, no terminal. You launch the app and you are at a Linux desktop.<br>I was inspired in part by Craig Loewen's Herbert demo. I had to take it a bit further because I have a problem.<br>I will say this up front. It is a toy. The build steps require compiling unstable WSL from main to get the container runtime early, it shoves Fedora desktop packages onto a server distribution that was never meant to have them, and it leans on an early source build of a WinUI experiment.<br>GitHub - sirredbeard/azurelinux-desktop: Azure Linux. In a container. On WSL. In a .NET app. With some whimsical desktop goodness.<br>Azure Linux. In a container. On WSL. In a .NET app. With some whimsical desktop goodness. - sirredbeard/azurelinux-desktop<br>GitHubsirredbeard
The four pieces<br>Four things from Build 2026 do the work here. Each one is interesting on its own. Together they make the demo.<br>The wslc container API<br>wslc is the new Linux container runtime for Windows. I wrote about it separately, but tl;dr it runs OCI containers natively in Windows, with a CLI and an API. This app uses the API directly: it creates a session, loads an image, creates a container with a port mapping, and starts it.<br>wslc has not landed in WSL yet. It will, in a few weeks. through wsl.exe --update --pre-release before it goes stable in WSL. The code is already in WSL though, which is open source, so you can build it from main and use it early if you want. YMMV.<br>WinUI Reactor, and no XAML<br>The app is a Microsoft UI Reactor app. Reactor is new a code-first way to build WinUI 3 interfaces: you write the UI as composable functions and state hooks in C#, the way you would in React, instead of authoring XAML and code-behind. There is not a single .xaml file in this project. Thankfully.<br>The whole interface is built in App.cs from Reactor factories: a title bar, a boot page, and the desktop surface, switched by state. The boot screen and the embedded desktop are both Reactor elements.<br>Azure Linux 4.0<br>Azure Linux 4.0 is the base image. It is Microsoft's Linux distribution, and version 4.0 is built from a snapshot of Fedora Linux 43. That detail matters for this project, because Azure Linux ships no desktop or GUI packages. It is a general purpose server and container distribution.<br>Because it is a Fedora 43 snapshot under the hood, you can point at Fedora 43 repositories and pull XFCE in from there, and...it mostly works. This is a bad hack and I would not do it in anything real, but it is a good illustration of what a shared package lineage buys you. Yay open source, again.<br>.NET 10<br>The app targets .NET 10 and WinUI 3, packaged through the Windows App SDK. dotnet run launches it with package identity, ReadyToRun precompiles for a faster cold start, and a single publish command produces an x64 or ARM64 build. The whole thing is one .slnx you build with dotnet build.<br>How it works<br>The flow is short. The app opens to a boot screen with the Azure Linux logo and a spinner. Behind that page it makes sure the desktop image exists, building it on first run, then asks wslc to start the container. The container runs XFCE behind an XRDP server. The app connects to that server over loopback, parks the Windows RDP client over the window, and when the session is on screen it unmounts the boot page. The window becomes the desktop.<br>The RDP client signs in automatically and fills everything below the title bar. From the outside it looks like the app simply is a Linux desktop. There is no visible container, no visible RDP prompt, no visible plumbing.<br>Some neat hacks<br>The interesting parts are where these pieces did not fit together cleanly. A few of my favorites.<br>The boot spinner is real composition, not a GIF<br>The Windows-style boot circle on the loading page is six dots orbiting a center, and they bunch and spread the way the real OS boot spinner does. It is built as raw composition visuals: each dot is a sprite shape whose offset runs a looping Vector3 keyframe animation sampled from an eased sweep, with each dot lagged in time so they trail. It starts on mount, loops forever on the compositor, and runs no managed code per frame.<br>Hosting the RDP control under WinUI<br>The desktop surface is the Windows RDP client ActiveX control, mstscax.dll. Really. Getting it to paint inside a WinUI window took...work. Its DirectX presenter never paints when the control is reparented under a WinUI DesktopChildSiteBridge, and the control crashes outright if you...