Microsoft has released the public preview of Azure Linux 4.0, bringing significant updates to its RPM-based distribution derived from Fedora, on June 2, 2026. The new version is now available for evaluation on Azure virtual machines, Virtual Machine Scale Sets, and other Azure compute services. This release marks the first major version increment since Azure Linux 3.0, promising enhanced performance, tighter Azure integration, and a refreshed software stack.

Azure Linux—formerly known as CBL-Mariner—is Microsoft's own Linux distribution, purpose-built to provide a consistent, secure, and lightweight foundation for cloud and edge workloads. It serves as the base operating system for many internal Microsoft services, including Azure Kubernetes Service (AKS) infrastructure, and is increasingly positioned as the recommended Linux environment for Azure customers. The distribution adheres to an RPM-based packaging model and draws heavily from Fedora, incorporating a curated set of packages optimized for cloud scenarios.

What’s New in Azure Linux 4.0

The jump to version 4.0 introduces a rebased system on a recent Fedora release, bringing thousands of updated packages and the latest long-term support (LTS) Linux kernel 6.x. While Microsoft has not disclosed the exact Fedora version, the move ensures compatibility with modern hardware, improved filesystem support, and better energy efficiency for scale-out deployments.

Kernel and Core System Updates
- Linux kernel 6.x LTS, providing enhanced security mitigations, improved I/O schedulers, and support for newer Azure VM types.
- Updated systemd, glibc, and OpenSSL for better performance and compliance.
- Faster boot times and reduced memory footprint, critical for containerized and ephemeral workloads.

Azure-Optimized Enhancements
Azure Linux 4.0 deepens its direct integration with Azure services:
- Preconfigured with Azure Instance Metadata Service (IMDS) optimizations.
- Supports Azure Boost networking and storage acceleration out of the box.
- Integrated Azure Monitor Agent for seamless observability.
- Faster disk encryption with Azure Disk Encryption using new encryption algorithms.

Security by Default
Security remains the cornerstone of Azure Linux. The 4.0 preview ships with:
- Signed packages and repository metadata by default, preventing tampering.
- SELinux enforcing mode enabled for all critical services.
- Strict firewall policies limiting inbound connections.
- Automated vulnerability scanning and patch delivery through Azure Update Manager.
- Support for Confidential Computing VMs with protected memory regions.

Installation and Availability

The public preview can be deployed directly from the Azure Marketplace or via Azure CLI templates. It is available for all current Azure VM families, including general-purpose (Dv5, Ev5), memory-optimized (Mv3), and GPU-enabled (NCasT4_v3) series, as well as Azure Kubernetes Service node pools.

To get started, navigate to the Azure Marketplace and search for "Azure Linux 4.0 Preview." Alternatively, use the following CLI command to create a VM:

az vm create \
  --name my-azure-linux-vm \
  --resource-group myResourceGroup \
  --image AzureLinux:azure-linux:4.0:latest \
  --generate-ssh-keys

For Virtual Machine Scale Sets, the process is similar, enabling rapid scaling with consistent configuration. Image-based deployments also support cloud-init customization for initial provisioning.

Performance and Compatibility

Azure Linux 4.0 is engineered for minimal disk and memory usage, making it ideal for high-density hosting. In internal benchmarks, the preview demonstrates up to 15% faster boot times compared to version 3.0 on the same VM types, largely due to kernel improvements and a slimmer initrd. The distribution retains compatibility with standard Linux tooling, so existing scripts, configuration management systems (Ansible, Chef), and monitoring solutions work without modification.

Compatibility highlights:
- Full RPM compatibility—users can install packages from official repositories or bring their own.
- Support for live migration and Azure Site Recovery, ensuring high availability.
- Works with all Azure storage types, including Premium SSD v2 and Ultra Disk.
- Container-optimized: includes runc, containerd, and CRI-O runtimes for seamless Kubernetes operation.

The Fedora Advantage

Azure Linux’s Fedora lineage means it inherits a modern, modular base while Microsoft applies its own hardening and tuning. Unlike raw Fedora, Azure Linux strips away unnecessary components, replaces standard kernels with Azure-tuned builds, and enforces compliance with Microsoft’s supply chain security requirements. This approach balances innovation with operational stability—critical for enterprises running 24/7 services.

The distribution follows a fixed lifecycle policy: each major release receives 3 years of critical and security updates, with an option for extended support via Microsoft’s Unified Support. Preview builds like 4.0 are intended for testing and feedback, not production use, but they offer a glimpse of the final experience.

Community and Ecosystem Feedback

Early testers on the Azure Linux GitHub repository have noted smoother package management with updated DNF and improved dependency resolution. While the public preview only launched hours ago, the response on technical forums has been cautiously optimistic. Windowsforum discussions reflect curiosity about long-term support for desktop-like workloads, though Microsoft has consistently emphasized that Azure Linux is a server- and container-oriented OS—not a general-purpose desktop replacement.

Feedback channels include the project’s GitHub issues page and the Azure Linux Q&A on Microsoft Learn. Microsoft encourages users to report bugs, particularly around driver compatibility and package conflicts, to refine the image before general availability.

What This Means for Azure Customers

Azure Linux 4.0 aligns Microsoft’s cloud infrastructure more closely with the open-source Fedora ecosystem, providing a familiar yet optimized stack for developers and operators. For organizations already running Fedora-based workloads, migration to Azure Linux can reduce licensing uncertainty and improve compliance with Microsoft’s security baseline.

Competing distributions like Ubuntu and Red Hat Enterprise Linux continue to dominate Azure’s Linux market, but Azure Linux offers unique advantages: no external licensing costs, deep Azure integration, and first-party support directly from Microsoft. As more Azure services adopt Azure Linux internally, customers who mirror that environment gain consistent performance and reduced troubleshooting overhead.

Looking Ahead

The public preview phase is expected to last several months, with a general availability release tentatively scheduled for late 2026. Microsoft will use this period to gather telemetry, refine kernel parameters, and ensure all Azure regions are fully supported. Subsequent updates will focus on container-native features, such as integrated support for Kata Containers and Wasm runtimes, positioning Azure Linux as the premier operating system for next-generation cloud-native applications.

For Windows enthusiasts invested in the Microsoft ecosystem, Azure Linux 4.0 represents the company’s ongoing commitment to hybrid computing—where Linux and Windows coexist seamlessly, each playing to its strengths. The preview is a practical step toward a unified cloud platform that transcends operating system boundaries.