Microsoft Launches Azure Linux 4.0 Server OS

MINNEAPOLIS – Microsoft has officially launched Azure Linux 4.0, marking a significant step in the company's embrace of open-source technology. The new distribution, based on Fedora Linux, is now available as a general-purpose virtual machine image for all Azure cloud customers. This release effectively transforms what was previously an internal and limited-use operating system into a widely accessible cloud platform.

The announcement came during Open Source Summit North America, where Brendan Burns, corporate vice president of Azure Cloud Native and Management Platform and Open Source at Microsoft, revealed the news. "We're going to be having Microsoft's open-source Linux distribution, a supported version of Linux supported by Microsoft, available on Azure, out for anybody to use," Burns stated. This declaration surprised many in the tech community, given Microsoft's historical stance on Linux.

Azure Linux 4.0 is built upon the Fedora ecosystem, leveraging its RPM package management. Microsoft curates the packages and manages the supply chain to ensure they are optimized for its Azure cloud platform. This ensures a purpose-built operating system that integrates vertically into Microsoft's infrastructure for a tailored Azure Linux experience.

A Shift from Container Focus to General Purpose

Previously, Microsoft's efforts in Linux distributions for Azure were more focused on specific use cases. CBL-Mariner, later renamed Azure Linux, served as a container software platform. More recently, Flatcar Container Linux has been productized as Azure Container Linux (ACL), a hardened, immutable container host specifically for Azure Kubernetes Service (AKS) users. Lachlan Everson, Microsoft's principal program manager on Azure's open-source team, explained the evolution. "We've been running Azure Linux for many years internally, and we got through to 3.0, and we only allowed it on as a container host on AKS. What we've done is make it a general-purpose," Everson said, highlighting that this latest version incorporates learnings from the heritage of Mariner.

While Azure Linux 4.0 is primarily offered as a VM image for cloud deployments, Microsoft is also developing support for Windows Subsystem for Linux (WSL). This will enable developers to run Azure Linux locally on their Windows 11 machines, providing a consistent development environment that mirrors the cloud platform. However, Everson clarified that there are "no plans" for a graphical desktop environment, emphasizing its optimization for server-side cloud operations with minimal packages.

Azure Container Linux, meanwhile, continues to build on the Flatcar project. It remains an immutable, secure-by-default operating system designed for container workloads within AKS. The immutable nature means there's no traditional package manager; system modifications are not permitted, with customer workloads running exclusively in containers. This approach enhances security and stability for containerized applications.

For existing users of Azure Linux 3.x, Microsoft has promised a smooth transition. "Yes," Everson confirmed when asked if users could simply upgrade without a full migration. The company is offering two years of support for each version, aiming to keep kernel choices stable throughout that period while providing upgrade pathways. Monthly security updates are also part of the support lifecycle, reinforcing Microsoft's commitment to security in an era of increasing cloud threats. The company emphasizes its control over the entire supply chain, from kernel selection to package curation, as a key security advantage.