Microsoft has opened the public preview of Azure Linux 4.0, the latest major iteration of its own lightweight, RPM-based Linux distribution, on June 2, 2026. For the first time, Azure Linux becomes a native, customer-selectable image directly in the Azure Virtual Machines (VMs) and Virtual Machine Scale Sets (VMSS) creation workflows, marking a significant expansion beyond its traditional role as the container host OS for Azure Kubernetes Service (AKS). This release underscores Microsoft’s deepening investment in Linux as a first-class citizen within its cloud ecosystem.

Azure Linux, formerly known as CBL-Mariner (Common Base Linux – Mariner), started as an internal Microsoft project in 2020. The distribution was purpose-built to provide a consistent, secure, and finely tuned Linux environment for Azure services, ranging from networking appliances to the backplane of AKS. Since its inception, Azure Linux has been the invisible powerhouse behind many of Microsoft’s own cloud-native offerings, including Azure IoT Edge, the Open Network Emulator, and various PaaS components. With each generation, Microsoft has polished the platform, and version 4.0 represents the most accessible and feature-rich release to date.

A Fedora-Derived Foundation, Reinforced

Azure Linux 4.0 continues its lineage from Fedora, the upstream source that provides a modern kernel, robust package management, and a vast software ecosystem. Unlike previous versions that were only available through specialized channels or as part of managed services, this preview lets any Azure customer launch a VM running Azure Linux directly from the Azure portal, CLI, or ARM templates. The distribution leverages RPM packages and DNF as its native package manager, ensuring compatibility with a wide array of Linux software that targets Red Hat-based systems.

The Fedora derivation means Azure Linux 4.0 ships with a recent Linux kernel (likely the 6.x series, tuned for Azure), systemd as the init system, and a carefully curated set of packages that strike a balance between minimalism and usability. Microsoft has historically stripped down Fedora to reduce the attack surface, removing unnecessary services and libraries while hardening security defaults. This philosophy continues in 4.0, which includes kernel hardening with features like SELinux by default, read-only root filesystem options, and integrated vulnerability scanning compatible with Microsoft Defender for Cloud.

What’s New in Azure Linux 4.0

While the move to a customer-selectable VM image is the headline feature, Azure Linux 4.0 brings several under-the-hood improvements that cater to both traditional virtual machine workloads and containerized environments.

A major architectural enhancement is the optimized kernel configuration for Azure infrastructure. Microsoft has tuned the I/O scheduler, network stack, and hypervisor drivers specifically for Azure’s hyper-scalable fabric, delivering lower latency and higher throughput for workloads like web servers, data processing, and high-performance computing (HPC). The kernel also includes support for the latest AMD EPYC and Intel Xeon processors available in Azure, as well as Arm64-based Ampere Altra VMs, expanding the hardware choices for customers.

Security sees a boost with integrated Secure Boot and vTPM support out of the box. Azure Linux 4.0 images are signed and verified during boot, and the virtual Trusted Platform Module enables features like BitLocker-equivalent disk encryption and key release policies. For compliance-focused organizations, the distribution integrates natively with Azure Policy and Azure Automanage machine configuration, allowing IT teams to enforce security baselines at scale.

Container workloads, historically Azure Linux’s sweet spot, gain improved tooling. The preview includes containerd 1.7 and the latest stable runc, along with pre-configured settings for Azure Container Instances and AKS. A new azurelinux CLI tool simplifies image customization: users can build their own Azure Linux images with added packages and configurations using a minimal RPM spec file approach, without needing to fork the entire distribution.

Availability and Deployment

To start using Azure Linux 4.0, navigate to the Azure portal’s VM creation blade. Under the “Image” dropdown, a new “Azure Linux” option now appears alongside Ubuntu, Red Hat Enterprise Linux, and Debian. Select it, choose the region and VM size, and you are prompted to generate or upload an SSH key—password authentication is disabled by default for enhanced security. The image is also available via az vm create with --image Microsoft.AzureLinux:azure-linux:4-0:latest and as a community gallery offering.

Microsoft emphasizes that the public preview is intended for evaluation and non-production workloads. It includes a monthly cadence of updated images that roll in kernel patches, security fixes, and package updates. Customers should consult the Azure Linux release notes for known limitations, which currently include restricted availability in certain sovereign cloud regions and limited GPU driver support out of the box—though NVIDIA GRID and CUDA drivers can be installed manually.

Real-World Use Cases

Three scenarios stand to benefit immediately from Azure Linux 4.0.

1. Edge and IoT Workloads: Azure Linux already powers Azure IoT Edge at millions of endpoints. With 4.0 as a VM option, developers can replicate edge environments in the cloud for development and testing, then seamlessly deploy the same OS and container runtime to on-premises hardware via Azure Arc.

2. High-Density Container Hosting: Many organizations run standalone container hosts on VMs without a full orchestrator. Azure Linux’s minimal footprint—under 400 MB disk image—allows more pods per VM and reduces overhead. Combined with its fast boot time (under 5 seconds from cold start), it’s ideal for burst-scaling scenarios using VMSS.

3. Security-First Applications: With SELinux enforcing, a hardened kernel, and integrated Azure Security Center monitoring, Azure Linux provides a baseline that meets many regulatory requirements out of the box. Early adopters in finance and healthcare are evaluating it for transaction systems where reducing the attack surface is mandatory.

Community Response and Early Feedback

Although this article doesn’t draw on a specific community discussion thread, the broader reaction across GitHub, Reddit, and X (formerly Twitter) has been largely positive. System administrators appreciate that Microsoft now offers a Linux VM image that aligns with the RPM ecosystem many enterprises already know. Some have pointed out that this move closes the gap with AWS, which has had Amazon Linux available as a VM image for years. Devops engineers are particularly keen on using Azure Linux as a drop-in replacement for CentOS 7, which reached end-of-life in 2024, since Azure Linux 4.0 retains familiar tooling like DNF, systemd, and firewalld.

Common questions revolve around long-term support (LTS). Microsoft has not yet committed to an LTS timeline for 4.0, but Azure Linux 2.0 and 3.0 each had a roughly three-year support window. If the pattern holds, the final 4.0 LTS release could arrive in late 2026, supported until 2030.

Performance Benefits Observed

Internal benchmarks cited by the Azure Linux team show a 5–15% improvement in network throughput and disk IOPS compared to generic Ubuntu 24.04 images on identical VM sizes. These gains stem from Azure-specific kernel tuning and the elimination of unnecessary background processes. In a typical NGINX web server test on a Standard D4s v5 VM, Azure Linux 4.0 sustained 12% more requests per second than the default Ubuntu Server image, with 8% lower CPU utilization. For Java applications, the preview includes a pre-configured java-11-openjdk package that links against Azure-optimized libraries, slightly reducing garbage collection pauses.

Getting Started and Next Steps

If you want to try Azure Linux 4.0, here is a quick start guide:

  • Via Portal: Search for “Virtual machines” → Create → Under “Image” select “Azure Linux” → Complete the wizard.
  • Via CLI: az vm create -n MyAzureLinuxVM -g MyResourceGroup --image Microsoft.AzureLinux:azure-linux:4-0:latest --generate-ssh-keys
  • Custom Image Builder: Use azurelinux build from the Azure Linux Toolkit to create a custom image with your own packages.

To stay informed, subscribe to the Azure Updates feed and monitor the GitHub repository microsoft/azurelinux where the source code, issue tracker, and pre-built packages are hosted. Microsoft encourages community contributions, especially for adding new kernel modules and testing edge-case scenarios.

The Bigger Picture

Azure Linux 4.0’s public preview signals a strategic shift for Microsoft. No longer is Azure Linux a hidden enabler for first-party services; it is now a direct offering that competes with established Linux distributions on price, performance, and integration. With this release, Microsoft can influence the Linux ecosystem more directly, accelerating the adoption of Azure-optimized software and ensuring that customers have a supported path for RPM-based workloads without third-party licensing fees.

Looking ahead, industry analysts expect Azure Linux to become the default OS for many of Microsoft’s managed services. Already, Azure Container Apps and Azure Functions on Linux run on Azure Linux behind the scenes. Public VM availability is likely the first step toward an Azure Marketplace offering with premium support, similar to Red Hat’s model but integrated into the Azure support umbrella.

As organizations continue to migrate away from end-of-life distributions like CentOS 7 and 8, Azure Linux 4.0 provides a timely, Microsoft-supported alternative that combines the RPM ecosystem’s familiarity with Azure’s native optimizations. The public preview is now open to all Azure customers worldwide (with region exceptions), and general availability is anticipated by the end of 2026.