Linux has been Azure's most popular server OS for nearly a decade. Now Microsoft is handing customers the ISO to run its own Linux distribution anywhere, and one veteran analyst thinks that spells trouble for Windows Server.
Azure Linux 4.0, previously internal cloud plumbing under the name CBL-Mariner, hit a new milestone this week. The Fedora-derived OS is now available as a downloadable ISO from Microsoft's GitHub, not just through the Azure Marketplace.
Both x86-64 and ARM64 images are live for anyone to install on local servers or virtual machines. The distribution ships with a hardened Linux kernel 6.18 tuned for Hyper-V and Azure VM performance, SELinux-based security defaults, and no graphical interface. It uses dnf5, the same package manager Fedora and Red Hat use, replacing the custom tdnf tool from earlier versions.
The base image weighs roughly 300 MB, stripped to only what cloud and server workloads need. Even basic tools like less are absent by design.
Microsoft's principal program manager for Azure open source, Lachlan Evenson, told ZDNET that the company chose Fedora as its upstream so Azure Linux could tap into the RPM ecosystem while Microsoft curates packages and the supply chain specifically for Azure's infrastructure. The build system uses TOML configuration files to produce signed RPM repos, Virtual Hard Disks, container images, and bootable ISOs.
ZDNET's Steven Vaughan-Nichols, who has covered Microsoft for decades, wrote that he can "see Microsoft eventually retiring Windows Server once and for all in favor of its own Linux server." It is not a fringe take: Linux already dominates Azure more than Windows Server does, and Microsoft is the only major cloud provider without a first-party Linux distro in the market. Amazon has Amazon Linux.
Google has Container-Optimized OS. Now Microsoft has Azure Linux. But running the OS outside Azure comes with a clear catch.
Microsoft's GitHub page states that "support for the ISO is community-based" and that "bare metal, ISO images, on-premises, and other clouds aren't supported." Formal support and SLAs only apply when deploying through the Azure Marketplace.
The preview also ships with OpenSSL 3.5 including post-quantum cryptography support for CRYSTALS-Kyber and CRYSTALS-Dilithium, Python 3.14 with a JIT compiler, and glibc 2.42. FIPS 140-3 certification is still in progress and will not arrive until general availability later in 2026.
Azure Linux is not a general-purpose desktop OS. It is a purpose-built server distribution that has already run production workloads for LinkedIn and Databricks at scale, with Databricks migrating more than 100,000 VMs and over a million CPU cores with zero customer-facing incidents. The ISO release is the first time that infrastructure is available to anyone, not just Microsoft's internal teams.
A companion product, Azure Container Linux, ships as an immutable, read-only image for Kubernetes nodes and is already generally available. The two share the same kernel and security update cadence but target different use cases.
The preview carries a strict not-for-production warning. Microsoft expects general availability later in 2026, with potential long-term support branches modeled on Fedora's release cycle.
