OpenVZ- Concept of Container, Hardware Node and CT0


    A container (otherwise known as CT, Virtual Environment (VE), Virtual Private Server (VPS) etc.) is one of the main concepts of OpenVZ.
    Container is an isolated entity which performs and executes exactly like a stand-alone server. Container can be rebooted independently and have root access, users/groups, IP address(es), memory, processes, files, applications, system libraries and configuration files.

    OpenVZ allows to have multiple CTs on a single Hardware Node. Every container has a ConTainer's IDentifer (CTID) which is used to manage the container.
     The OpenVZ software reserves the IDs ranging from 0 to 100. Though OpenVZ uses only ID 0, future versions might use additional Container IDs for internal needs. Do not create Containers with IDs below 101.

Hardware Node:-

    Hardware Node (otherwise known as host system) is a term used in OpenVZ. Basically it means the physical server on which OpenVZ is installed and running. Sometimes Hardware Node is abbreviated as HW or HN.


    In OpenVZ, you have multiple CTs, as well as the host system  itself, which is otherwise known as CT0 or VE0. In other words, CT0 means the server itself. From CT0, we can use vzctl and other tools to manage containers. From CT0, all the containers' processes, files, etc. are accessible. From CT0, we manage the hardware, install a new kernel, etc.
CT0 - Container Zero
Container ID Zero is given to the Hardware Node itself.