Dom0

Dom0, short for domain 0, is the privileged domain in the Xen hypervisor architecture. It is the initial domain started by the Xen hypervisor at boot and has direct access to hardware resources and to the Xen management interfaces. Dom0 holds the control plane for the host, including the hypervisor’s management tasks and the I/O infrastructure that serves other domains.

In typical deployments, Dom0 runs a general-purpose operating system such as Linux and provides the kernel and userland necessary to manage the virtualization environment. It hosts the device drivers that interact with physical hardware and expose virtualized devices to other domains through backend drivers. The front-end drivers in user domains (DomUs) communicate with these backends in Dom0 to access virtual block devices, network interfaces, consoles, and other I/O resources.

Dom0 is responsible for creating, starting, stopping, and migrating other domains (DomUs), allocating memory, and coordinating scheduling and resource management across the host. It also maintains configuration data and state via the XenStore and Xenbus, which DomUs read to discover available devices and services. Management tools and interfaces, such as command-line utilities and APIs, typically run in Dom0 and communicate with the Xen hypervisor to perform administrative tasks.

Security and isolation considerations note that Dom0 represents a high-security risk surface because it has privileged access to hardware and the hypervisor. Some Xen deployments mitigate this risk by using driver domains or alternative architectures that place device drivers in separate domains, reducing the amount of trust placed in Dom0. Nevertheless, Dom0 remains the conventional hub for management and I/O in many Xen systems.