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ZDNET’s key takeaways
- Microsoft has launched its first complete Linux distribution: Azure Linux 4.0
- Azure Linux has been divided into Azure Container Linux and a new virtual machine edition called Azure Linux.
- Microsoft is essentially acknowledging that it has become a Linux-driven company.
Minneapolis – There I sat at the Open Source Summit North America, listening to Brendan Burns—Kubernetes co-founder and Microsoft’s current Corporate VP of Azure Cloud Native and Management Platform, and Open Source—discuss the shift from open-source to agentic AI. Midway through his talk, he dropped a bombshell: “When I joined Azure a decade ago, Linux wasn’t the dominant operating system powering the Azure cloud. Over the past 10 years, it has become the dominant operating system on Azure. And today, I’m thrilled to announce that Microsoft’s open-source Linux distribution—a Microsoft-supported version of Linux—is now available on Azure for anyone to use.”
I did a double take. Backstage, Jim Zemlin, CEO of the Linux Foundation, looked equally stunned, and every Linux enthusiast in the audience murmured in surprise.
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Microsoft has previously released Linux-based products. The first was the Azure Sphere edge computing device. That was followed by CBL-Mariner, a Linux-based container platform, which was later rebranded as Azure Linux. But until this moment, Microsoft had never offered a general-purpose Linux distribution.
And that was the entire announcement. Zemlin brought Burns back on stage and asked if he had truly just unveiled a Microsoft Linux distro. Burns confirmed he had. Zemlin responded, “When Microsoft joined the Linux Foundation, there were wild conspiracy theories that the Linux Foundation was somehow compromising open source by partnering with Microsoft—and now you’re announcing that you’re shipping a Linux distribution. That’s incredible.”
He’s absolutely right. We’ve traveled a long road since former Microsoft CEO Steve Ballmer famously labeled Linux a cancer. Now, Burns reflected, “It’s been an incredible journey, and it’s been wonderful to see the entire company embrace it.”
So why did this news catch everyone off guard? The announcement was originally scheduled for Microsoft Techcon in two weeks, but at the eleventh hour, they chose to reveal it early.
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Burns departed the conference before I could get additional details, but the Linux Foundation’s PR team quickly arranged a meeting with Lachlan Everson, Microsoft’s Principal Program Manager on Azure’s open-source team. He explained that Microsoft is transforming Azure Linux into a fully capable general-purpose cloud distribution with Azure Linux 4.0, while simultaneously productizing Flatcar Container Linux as a hardened, immutable container host named Azure Container Linux (ACL).
The former serves as a general-purpose virtual machine (VM) image for all Azure customers, not limited to Azure Kubernetes Service (AKS) users. Until now, Everson explained, “Azure Linux was only accessible to third-party customers through AKS specifically, and that was Azure Linux 3.0.” Moving forward, that role will be filled by ACL.
Everson highlighted that Azure Linux 4.0 represents years of internal refinement and the evolution of the earlier Mariner distribution. “We’ve been running Azure Linux internally for many years, and we reached version 3.0, but only permitted it as a container host on AKS. What we’ve done now is make it general-purpose—this incorporates all the knowledge we’ve gained from the Mariner lineage.”
Fedora-based, open source, Azure-optimized
At its core, Azure Linux 4.0 is built on Fedora Linux and is published as an open-source project on GitHub. The code is live right now. Yes, Red Hat is fully aware of what Microsoft has done. Everson added, “We made the decision to use Fedora as our upstream, so it leverages RPMs within the Fedora ecosystem. Microsoft curates the packages and the supply chain to align with Azure’s cloud platform.” Microsoft also engineered it to be “purpose-built for Azure, integrating vertically across all of our infrastructure to deliver the best possible Azure Linux experience on Azure.”
While Azure Linux will be distributed as a VM image, Microsoft is already laying the groundwork for developers on Windows desktops: “As of today, it’s available as a VM image for your VM host on Azure. We’ll also be announcing WSL images.”
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Although developers will be able to run Azure Linux locally via WSL, Microsoft isn’t marketing it as a conventional desktop Linux. When asked whether he could install it on his laptop, Everson replied: “I’ll be able to run it on my laptop, or whatever. Yes, on Windows 11.” However, when questioned about a desktop experience, Everson was firm that there are “no plans” for a graphical interface.
“It’s optimized for server-side cloud workloads,” he said, adding that even on a developer’s machine, users should expect a streamlined setup. “Minimal packages, exactly. The goal is to give you a consistent development experience on your local machine, so you can build your workloads there and run them with VS Code. You can deploy your applications on it and know that the platform matches what you’re running in the cloud—giving you that seamless consistency between environments.”
Azure Container Linux
Flatcar continues to serve as the upstream project, but Microsoft is packaging it specifically for Azure customers. Everson described Flatcar as “a purpose-built, immutable, secure-by-default, production-ready operating system, and Azure Container Linux is the productized version of that. We’re still investing in the upstream Flatcar ecosystem and pulling those improvements downstream into a polished, productized experience tailored for container workloads—specifically container hosting in AKS.”
To emphasize the immutable design, he added, “Everything is pre-baked in, so there’s no package manager. We compile the components into the immutable image, and they remain fixed in that immutable version. Azure Container Linux is that immutable version. You shouldn’t be modifying any system packages or application packages. Any changes you need to make should be handled through customer workloads running in containers.”
Lifecycle, support, and upgrades
For current Azure Linux 3.x users, Microsoft is promising a smooth transition rather than a disruptive migration. When asked about moving from “Azure Linux free,” Everson simply said, “Yes,” confirming that users could “just upgrade” without a full migration. He then detailed the support timeline: “We provide two years of support.”
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Within that support window, Microsoft aims to maintain kernel stability while offering upgrade options. “We select specific kernel versions that we commit to for the duration of the two-year support period for each release, and we also provide an upgrade pathway for customers. So it’s fully supported and upgradable throughout those two years.”
It follows a regular monthly security update schedule.
That said, security is a core focus for Azure Linux, particularly given the rise in kernel vulnerabilities in the AI era. Everson explained Microsoft’s advantage by emphasizing full control over the entire supply chain: “Part of our value is that we manage every component used to build the distribution—minimizing package surface area, using a curated kernel, and customizing it specifically for Azure hardware—all while delivering top-tier security.”
Microsoft commits to monthly patches for Azure Linux—just don’t call it Patch Tuesday. However, if a critical Common Vulnerabilities and Exposures (CVE) emerges, Microsoft pledges to release a patched image “as soon as those fixes are available.”
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The new Azure Linux also allows customers to offload much of the update management if they prefer. When asked whether users must manually stay current, Everson highlighted built-in automation: “Whether they’re VMs or AKS clusters, we offer opt-in automatic upgrades based on security needs.” In large-scale deployments, updates are rolled out gradually to prevent disruptions.
For customers running fragile or highly customized apps, opting out is still an option. “If you opt in, you’ll always be up to date and secure with the latest versions,” Everson noted, then added, “You can definitely opt out if needed.”
He linked this strategy to a proactive approach: “As Jim said, we must ensure customers can keep pace with the speed of disclosures and patches—so we’ve embedded that into the OS core, enabling rapid updates so you’re never left waiting.”
Positioning in the AI-native era and with partners
Everson described Azure Linux as a response to the “AI-native explosion” and Linux’s dominance as the foundation for modern AI workloads. “All AI applications run on Linux,” he said. Microsoft has “learned to build robust Linux images, and we want to give that to our customers so they can thrive in the AI-native era.”
At the same time, he emphasized that Azure Linux is meant to complement—not replace—other distributions in Azure’s catalog. Asked whether Red Hat was aware of the new offering, the answer was clear: “Actually, yes.” Everson added, “We still have a great partner ecosystem. This changes nothing. If you want Red Hat or Ubuntu, that’s absolutely fine. We saw an opportunity to offer a battery-included experience on Azure. We support eight endorsed distros and will continue working with them.”
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As Microsoft announced in a blog post, “Today, over two-thirds of customer cores in Azure run Linux, and platforms like Microsoft 365, GitHub, and OpenAI’s ChatGPT all rely on Linux. When ChatGPT scales across more than 10 million compute cores worldwide and handles a billion queries daily, Linux and Kubernetes make it possible.”
So here we are. Microsoft runs its most critical services on Linux. It only makes sense that Microsoft is now offering a complete, server-focused Linux distribution—while continuing to support multiple other Linux distros. Today, Microsoft has finally acknowledged that, outside the desktop, it is primarily a Linux company.
