Domain0
Xen virtualization environment with domain (Domain) to describe various virtual machines, each domain has its own ID and other properties, thus each virtual machine is often expressed Domain 0 , Domain. 1 and the like, may be used a shorthand way, as the dom0 . Dom0 is a unique virtual machine running on Xen Hypervisor . Its operating system kernel is a specially modified Linux kernel, which can directly access hardware I/O resources and interact with other virtual machines. Other domains do not have direct access to hardware I/O resources and are highly isolated from each other. Therefore, dom0 is also called a privileged domain, and other domains are collectively called DomU (Unprivileged Domain) . It should be noted that DomU implements I/O functions through Dom0 . Therefore, Dom0 must be started before DomU runs
DomainU
DomU is a non-privileged domain, and they have no right to directly access hardware resources. Xen supports two different types of virtualization modes: PV (Paravirtualization) and HVM (Hardware-assisted or Full Virtualization) , which can run on the same Xen Hypervisor at the same time , and can even use PV technology in the HVM environment , which is also called PV on HVM .
Xen Hypervisor is an intermediate software layer that runs between a physical server and an operating system. It allows multiple operating systems and applications to share a set of basic physical hardware, so it can also be regarded as a " meta " operating system in a virtual environment . It can coordinate access to all physical devices and virtual machines on the server, also called Virtual Machine Monitor ( Virtual Machine Monitor ). Hypervisor is the core of all virtualization technologies. The ability to support multi-workload migration non-disruptively is the basic function of Hypervisor . When the server starts and executes the Hypervisor , it allocates an appropriate amount of memory, CPU , network, and disk to each virtual machine, and loads the guest operating system of all virtual machines.