Steve Ballmer, then chief executive of Microsoft, once called Linux a cancer on his company’s business. Two decades later, the same firm ships its own Linux distribution, runs more than 60 percent of its Azure customer compute cores on Linux, and tells its own customers how to install Linux from its own website. The reversal is now part of Microsoft’s product copy, not a marketing experiment.
The shift is visible on Microsoft’s own Azure landing pages. Microsoft’s Linux VM product page opens with the line that “more than 60% of customer cores in Azure run Linux workloads,” and follows it with the concession that, “according to the Linux Foundation, Microsoft is a significant contributor to the Linux kernel.” The piece used to be competitors’ fight for the desktop. Today the fight is for cloud workloads, and Microsoft’s own product pages acknowledge that the workloads land on Linux.
WSL and the Linux Layer Inside Windows
The most public piece of the pivot is the Windows Subsystem for Linux, or WSL. According to the WSL documentation on Microsoft Learn, “Windows Subsystem for Linux (WSL) lets developers run a GNU/Linux environment” on Windows, “unmodified, without the overhead of a traditional virtual machine or dual-boot setup.”
The version Microsoft calls WSL 2 ships a real Linux kernel inside a lightweight virtual machine, instead of translating Linux calls into Windows calls the way WSL 1 did. A second component, WSLg, adds the desktop plumbing. Per Microsoft’s own project repository, “WSLg is short for Windows Subsystem for Linux GUI and the purpose of the project is to enable support for running Linux GUI applications (X11 and Wayland) on Windows.”
Linux graphical apps, audio, cut and paste between Windows and Linux windows, and a Linux terminal that sits inside Windows Terminal are now part of Microsoft’s default developer story on Windows. WSL itself is listed in Microsoft’s open-source project catalog, meaning the subsystem that runs Linux inside Windows is itself an open-source project built by Microsoft. The Azure VM page also bundles WSL into its pitch to Linux customers alongside bare-metal and virtual-machine installs.
| Attribute | WSL 1 | WSL 2 |
|---|---|---|
| Kernel | Translates Linux system calls into Windows calls | Runs a full Linux kernel inside a lightweight VM |
| GUI apps | Not supported | X11 and Wayland support via WSLg |
| Install path | Built into earlier Windows builds | Shipped via in-box component and Microsoft Store |
Azure Linux, the Distribution Microsoft Builds Itself
Microsoft no longer just runs Linux inside Windows or hosts other people’s Linux in the cloud. It builds a distribution. According to Microsoft’s Azure Linux 4.0 public-preview announcement at Microsoft Build in May 2026, “Azure Linux is a Fedora-derived, RPM-based Linux distribution built and maintained by Microsoft. It is open source, free to use, and optimized specifically for Azure.”
The same announcement lists internal scale the company is putting behind the build. “Azure Linux already powers millions of cores across Azure’s internal services, including AKS, Azure SQL, Azure Cosmos DB,” and customer migration numbers attached to it. Databricks, per the Microsoft post, “migrated over 100,000 VMs and more than 1 million CPU cores to Azure Linux with zero customer-facing incidents,” a figure the announcement cites alongside claimed improvements in image-pull speed and query execution. Microsoft also commits to bringing Azure Linux into Windows via WSL, so a developer can run the same OS locally that production runs on Azure.
Sixty Percent of Azure Customer Cores Run Linux
The headline number behind the pivot is the workload split inside Azure. Microsoft’s own Azure VM product page states it flatly: “More than 60% of customer cores in Azure run Linux workloads.” A separate Microsoft Mechanics blog post on running Linux on Azure repeats the figure and adds that “the vast majority of compute workloads, virtual machines and containers run Linux. It’s on more than 60% of all active customer compute cores.”
The same post notes that Microsoft itself runs a similar mix internally. “Microsoft has thousands of employees that use Linux as their primary OS,” the post says, and shows a workplace-provisioned Ubuntu laptop signed into Microsoft Intune. Microsoft’s own highest-profile services, including Azure OpenAI Service, Azure Kubernetes Service, the App Service, Cosmos DB, and Azure Database for PostgreSQL, the post states, “all run on Linux.”
- More than 60% of customer cores in Azure run Linux workloads (Microsoft Azure VM page).
- Azure Linux 4.0 entered public preview at Microsoft Build (May 2026).
- Databricks migrated more than 1 million CPU cores to Azure Linux with zero customer-facing incidents.
- Databricks also migrated more than 100,000 VMs to Azure Linux.
- Microsoft hosts thousands of internal employees on workplace-provisioned Linux machines.
SONiC, the Network Operating System Microsoft Gave the Linux Foundation
The pivot runs one layer deeper than the workload story: it touches the network itself. SONiC, Software for Open Networking in the Cloud, is the Linux-based network operating system Microsoft originally wrote for its own Azure data centers. In April 2022, SONiC’s move to the Linux Foundation (April 2022) was announced by the Foundation: “Created by Microsoft for its Azure data centers, SONiC is an open source network operating system (NOS) based on Linux that runs on over 100 different switches from multiple vendors and ASICs.”
Microsoft founded SONiC to bring high reliability and fast innovation to the routers in Azure cloud data centers. We created it as open source so the entire networking ecosystem would grow stronger. SONiC already runs on millions of ports in the networks of cloud scalers, enterprises, and fintechs.
Those are the words of Dave Maltz, Technical Fellow and Corporate Vice President of Microsoft Azure Networking, in the Foundation’s release. The Linux Foundation version of the project now counts Alibaba, Broadcom, Dell, Google, Intel, Microsoft, and NVIDIA as premier members, which is a long way from the company’s old position that open-source software undercut commercial software.
The Open-Source Catalog Spreads to Windows
Microsoft’s open-source footprint now reaches into Windows itself, not just into the Linux side of the company. The Microsoft open-source project catalog lists .NET as “Microsoft’s open-source, general-purpose development framework for building cross-platform apps,” and lists Windows Calculator as a Microsoft open-source project written in C++ and C# that ships pre-installed with Windows. TypeScript, another flagship Microsoft language, is hosted at typescriptlang.org and listed in the same catalog.
Other projects Microsoft ships as open source reveal how broad the line has become:
- .NET, the cross-platform application framework.
- Windows Calculator, the default Windows calculator app.
- Windows Terminal, the shell Microsoft bundles on Windows.
- SONiC, the Linux-based network operating system.
- TypeScript, the JavaScript superset language.
GitHub, the host of these and many more, is also a Microsoft property, and it is the platform where most of the open-source world ships code in the first place. The company whose 1976 founder wrote an open letter to hobbyists complaining about unpaid-for Altair BASIC now hosts much of the world’s unpaid collaboration on its own servers.
Why the Cloud Forced the Pivot
The driver sits underneath the product changes. Enterprise IT spends moved to subscription models and, more importantly, to cloud workloads, and Linux became the default operating layer for those workloads. Microsoft’s own marketing now treats Linux support as a cloud requirement, not a concession.
Azure’s Linux VM page lists engineering alliances with three of the biggest commercial distributions. “Microsoft has close engineering partnerships with SUSE, Ubuntu and Red Hat, three of the most popular distros,” the Microsoft Mechanics post states, and the Azure product page advertises that customers get “co-located technical support from Azure, Red Hat, and SUSE with just one ticket.” Microsoft’s Build 2026 surface hardware story, including a Linux-tuned developer box aimed at Linux AI work, ran in the same keynote where Azure Linux 4.0 was unveiled. The pattern is the same in both directions: customers want Linux where their workloads live, and Microsoft has decided to be the one who carries that Linux.
What Remains of the Old Rivalry
The pivot is real, but it is also partial. Azure Linux, per its Microsoft announcement, is “built exclusively for cloud and server workloads, it is not intended to support desktop usage or GUI applications.” WSL, in turn, is positioned by Microsoft’s Linux install guide as the recommended entry path, with bare-metal installs framed as the more complicated route for the curious.
Linux is no longer the rival. It is the substrate Microsoft builds part of its own business on, and the company says so in its own copy. The fight that defined personal computing for two decades has, for now, been settled by the cloud economy rather than by either side winning the desktop.
Frequently Asked Questions
Why did Microsoft start supporting Linux?
Microsoft’s own product copy frames Linux support as a response to where customer workloads now run. The Azure VM page says more than 60% of customer cores on Azure run Linux and credits the Linux Foundation with calling Microsoft a significant contributor to the Linux kernel.
What is the Windows Subsystem for Linux (WSL)?
Per Microsoft’s documentation, WSL lets developers run a GNU/Linux environment on Windows, unmodified, without the overhead of a traditional virtual machine or dual-boot setup. WSL 2 ships a real Linux kernel, and WSLg adds support for X11 and Wayland graphical apps.
What is Azure Linux?
Azure Linux is Microsoft’s own Linux distribution. Microsoft’s announcement describes it as a Fedora-derived, RPM-based distribution, open source and free to use, optimized for Azure, and built to power millions of cores inside Azure’s internal services.
How much of Microsoft Azure runs on Linux?
Microsoft’s Azure VM page states the figure directly: more than 60% of customer cores in Azure run Linux workloads. A separate Microsoft Mechanics post puts the number at more than 60% of all active customer compute cores.
Did Microsoft ever call Linux a ‘cancer’?
Yes. Then-CEO Steve Ballmer publicly called Linux a cancer on Microsoft’s business in the 2000s. The same company now ships its own Linux distribution and publishes customer-facing guidance on how to install Linux.
What is SONiC?
SONiC is Software for Open Networking in the Cloud, an open-source network operating system based on Linux that runs on switches from multiple vendors. Microsoft originally built SONiC for its Azure data centers and moved it to the Linux Foundation in April 2022.
What Windows components has Microsoft open-sourced?
Microsoft’s open-source project catalog lists Windows Calculator, Windows Terminal (parent app of WSL shells), and WSL itself. Microsoft’s general-purpose open-source projects include .NET and TypeScript.
