What is OpenVZ?

     OpenVZ (Open VirtualiZation) is an operating system-level virtualization technology based on the Linux kernel and operating system. OpenVZ allows a physical server to run multiple isolated operating system instances, known as containers, Virtual Private Servers (VPSs).OpenVZ is limited in that it requires both the host and guest OS to be Linux.

    OpenVZ is a virtualisation technology that was developed by Parallels, and is the basis for their Virtuozzo platform. OpenVZ consists of the open sourced parts of Virtuozzo.

    OpenVZ works somewhat like Solaris Zones or FreeBSD jails, in the aspect that it utilizes a single operating system kernel and creates various user-environments within the single operating system space. The various user-environments are called Virtual Environments, of VE.

    Users in a VE will have their own view on the available resources in the system. They are only able to see and interact with processes running in the same VE, they only have access to files and diskspace assigned to the VE and can only see network-traffic destined to the IP address assigned to the VE.

    Due to the fact that OpenVZ uses a single operating system kernel to provide various Virtual Environments the overhead of OpenVZ is very low. No memory is wasted by loading copies of the kernel for every VE, no translation is needed for I/O going to the storage or network.This allows for very lightweight VE’s, with some environments taking less then 8MB of memory and only a few megabytes of diskspace.

    Another advantage of OpenVZ is that it doesn’t require any hardware-assisted virtualisation on the system and it doesn’t need to ‘emulate’ any cpu or I/O instructions, which would put a large strain on the resources.
     Your files and processes are visible on the host-system, but hidden from other users of the system. Only the root-user on the host can access your resources. This access is also used to make backups of all your files, so System Administers can help you with a restore in case you accidentally erase some files.

     It is possible to mount iso images and use sshfs systems using fuse, but kernel-mode mounting is not available.

    A disadvantage of the OpenVZ VE’s is that only Linux environments are possible, since the kernel is shared between all environments it’s not possible for a VE to make modifications to the kernel. It’s also not allowed for the VE’s to change their IP-configuration, to act as NFS servers or to mount filesystems, as this would have an impact on the host’s security system.

Note:- You can refer the following links to know more about OpenVZ