Microsoft took a tough stance on the open source community 25 years ago, when then-CEO Steve Ballmer once described Linux as "a cancer that clings to everything in an intellectual property sense." Now, at the 2026 Build conference, Microsoft has not only become one of the important contributors to open source software, but also officially released its own Linux distribution Azure Linux 4.0 to the public. This change has attracted widespread attention in the industry.
Azure Linux 4.0 is a true open source Linux distribution fully maintained by Microsoft, built on Fedora 43, and has long been running at scale in Azure virtual machines and Microsoft internal infrastructure.
The so-called Linux distribution is based on the Linux kernel and integrates components such as package managers, system tools, default configurations, support systems, and graphical interfaces to form a complete operating system that can be actually deployed and used. Ubuntu, Fedora, Debian, Red Hat Enterprise Linux (RHEL), Arch Linux, etc. all share the same Linux kernel, but target different usage scenarios and user groups. Azure Linux 4.0 is a product that Microsoft has added to this list. It is based on Fedora 43 and follows the RPM package format and Red Hat ecosystem. However, Microsoft filters the package set, maintains security patches, and performs special optimization for Azure cloud workloads.
The predecessor of Azure Linux is the internal project CBL‑Mariner launched in 2019, which stands for Common Base Linux Mariner. The goal is to provide a lightweight and secure operating system in Azure infrastructure. By 2022, Azure Linux has been deployed at scale in production-grade services such as AKS (Azure Kubernetes Service), Azure SQL, Azure Cosmos DB, etc. LinkedIn also completed an overall migration to Azure Linux 3, while Databricks switched more than 100,000 virtual machines and more than one million CPU cores to the system without any major customer-facing failures. In March 2024, Microsoft officially renamed the system Azure Linux, and officially announced Azure Linux 4.0 at the North American Open Source Summit in May 2026, and then opened it for public preview during the Build 2026 conference in June.
Unlike general-purpose distributions like Ubuntu, Fedora, or RHEL, Azure Linux 4.0 is not an operating system for desktop or everyday use. It has no graphical interface, audio stack or desktop environment, and the base image doesn't even come pre-installed with common text paging tools like less, containing only the minimal components required for cloud and server workloads. After the installation is completed, the system directly enters a plain text console, with Bash as the default shell, and does not provide a graphical installer or desktop environment similar to the desktop version of Fedora or Ubuntu. The goal of this design is to reduce the overall size of the package as much as possible, thereby reducing the attack surface, reducing potential vulnerabilities that need to be patched every month, and making server and container environments run more predictably and efficiently.
In terms of deployment scenarios, Azure Linux is also significantly different from other distributions. Ubuntu Server, Fedora Server and RHEL have been streamlined compared to the desktop version, but still retain a lot of common components, and are officially supported to run on local data centers, other cloud platforms and physical servers. In contrast, Azure Linux 4.0 is positioned as a "cloud-specific distribution", mainly for Azure cloud servers and virtual machine workloads; although running outside Azure is technically feasible, it is not within the scope of Microsoft's official support. Its base image size is around 300 MB, while base images for Ubuntu, Fedora, or RHEL are typically 500–600 MB or more. Azure Linux 4.0 is free to use, with no operating system license fees. It is maintained by Microsoft and focuses on hardened security default configurations and rapid response to CVE vulnerabilities.
From the perspective of the technology stack, the current public preview version of Azure Linux 4.0 is equipped with the Linux 6.18 LTS kernel optimized for Azure, strengthens Hyper‑V integration, and supports GPU and AI accelerators. The package manager uses dnf5 instead - this is a new version of DNF rewritten in C++. Compared with the DNF implemented by the old version of Python, it is better in dependency parsing speed and resource consumption. The system uses glibc 2.42 as the C standard library, and the initialization system uses systemd 258. The distribution has built-in Python 3.14 and enables a new JIT compiler. It is also equipped with OpenSSL 3.5 that supports post-quantum cryptographic algorithms, covering the CRYSTALS-Kyber and CRYSTALS-Dilithium algorithms that have been standardized by NIST, which is of practical significance to enterprise users with compliance needs. The FIPS 140‑3 certification for Azure Linux 4.0 is still in progress and is expected to be completed before the general release (GA) in 2026.
Also unveiled at the same time as Azure Linux 4.0 is Azure Container Linux, the second Linux product launched by Microsoft at Build 2026. Although the two share the same kernel and security update cadence, there are fundamental differences in positioning: Azure Container Linux is an immutable system. The operating system is provided as a read-only image, and users cannot install new packages or modify system configurations at runtime. When an update is released, the platform will replace the system image as a whole and automatically roll back when an exception occurs. Azure Container Linux has been running silently under Azure Kubernetes Service (AKS) since 2023, and with the launch of version 4.0, it is available as a standalone product for the first time. In contrast, Azure Linux 4.0 is aimed at general cloud servers and virtual machines, allowing free installation of software packages. Updates are completed one by one through dnf5 by package. It is currently in the public preview stage, while Azure Container Linux has reached the mature state of "generally available".
From a business and strategic perspective, it's not surprising that Microsoft would create its own Linux distribution. Currently, the number of Linux instances among the operating systems running on the Azure cloud has exceeded that of Windows Server, and most of these Linux systems come from third-party vendors such as Ubuntu, RHEL, SUSE, and Debian. When customers run these systems on Azure, they often purchase support subscriptions from their respective distribution vendors; Microsoft provides the underlying infrastructure, but needs to share operating system-level revenue with these vendors. By driving customers to standardize the use of Azure Linux on Azure, Microsoft can achieve end-to-end unified control across the supply chain and technology stack, with every software package signed by Microsoft and a detailed software bill of materials (SBOM) published for each release. For enterprise teams in regulated industries, concentrating the entire operating system level responsibility on a single vendor is an important selling point.
This strategy is in line with other cloud giants: Amazon launched Amazon Linux, Google launched Container‑Optimized OS, and Microsoft followed this trend with Azure Linux. Microsoft has also made it clear that Azure Linux will be a consistent solution for development and production environments - develop using Azure Linux through WSL on local Windows, and then directly deploy the same environment to the Azure production environment to reduce the environmental difference problem of "it can run locally, but errors occur in the cloud". With the launch of WSL Containers in Windows 11, developers can build, run, and test Linux containers through WSL locally, and deploy them to Azure Linux with one click without leaving the Windows ecosystem.
For ordinary users, whether they need to pay attention to Azure Linux 4.0 can be viewed more realistically. Currently, Azure Linux 4.0 is still in public preview and is clearly marked "not for use in production environments." The target users are mainly developers and enterprise teams for Azure cloud servers and container workloads. If you use Ubuntu on your personal computer every day, or deploy distributions such as RHEL and Fedora in an enterprise environment, Azure Linux will not replace these mature products at this stage. More importantly, it shows that Microsoft has become a vendor that maintains a true production-grade Linux distribution that already hosts critical workloads in large Internet services such as LinkedIn and Databricks, and is starting to open it up to a wider user base as a first-class citizen option on the Azure platform.