CBL-Mariner

CBL-Mariner (Common Base Linux) is a free and open source cloud infrastructure operating system based on Linux and developed by Microsoft. It is used in Microsoft Azure and in the Windows Subsystem for Linux 2 to provide the ability of running Linux graphical user interface (GUI) apps on Windows 10.
Overview.
CBL-Mariner is being developed by the "Linux Systems Group" at Microsoft for its edge network services and as part of its cloud infrastructure. The company uses it as the base Linux for containers in the Azure Stack HCI implementation of Azure Kubernetes Service. In a similar approach to Container Linux, CBL-Mariner only has the basic packages needed to support and run containers.
Common Linux tools are used to add packages and manage security updates. Updates are offered either as RPM packages or as complete disk images that can be deployed as needed. Using RPM allows adding custom packages to a base CBL-Mariner image to support additional features and services as needed.
Notable features include an iptables-based firewall, support for signed updates, and a hardened kernel.
The system was open sourced by Microsoft in 2020. The source code is licensed under a mix of open-source licenses including the GNU General Public License and the MIT License and available on GitHub.
Prerequisites for building CBL-Mariner include the Go programming language, the QEMU utilities, as well as RPM.