Software-defined vehicles are those whose functionalities and features are primarily governed by software, thus allowing continuous updates, upgrades, and the introduction of new capabilities throughout their lifecycle. This shift from hardware-centric to software-driven architectures is a major transformation that reshapes not only product development and operational strategies but also business models in the automotive industry. An SDV operating system provides the base platform to manage vehicle software and enable those advanced functionalities. Unlike traditional embedded or general-purpose operating systems, it is designed to meet the particular demands of modern automotive architectures. Reliability, safety, and security become crucial because even minor faults may have serious consequences. Key challenges to be handled by the SDV OS include how to handle software bugs, perform real-time processing, address functional safety and SOTIF compliance, adhere to regulations, minimize attack surface exposure, and protect against remote access and data breaches. This is achieved via sound architectural principles, including a CSM for fine-grained access control, a lean and minimal kernel to reduce vulnerabilities, secure and efficient inter-process communication, and user-level drivers to provide better fault isolation. The key novelty of this approach rests on the fact that it uses open-source kernels, libraries, and tools that guarantee flexibility, clarity, and community-driven innovation. It provides a flexible runtime environment and OS-level isolation using virtualization, safe hardware sharing, and adherence to safety standards to set up the SDV OS as a resounding, secure, and future-ready base for next-generation automotive systems.