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My OpenVZ (debian) host environment has only the minimal packages installed. Now I was irritated to see a mysqld process in top when the mysql package is installed and running only in one container. So I killed it and saw the service down in the container. I can start it there again and everything is fine. But - was it not the idea of a virtual environment to separate the OS instances and their processes between host and clients?

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OpenVZ is not a virtualization solution - it's a container solution. There's only a single kernel instance, and that kernel knows about all processes running on the system, regardless of whether or not they're in a container.

For this reason and many others, OpenVZ is not well-liked among professional sysadmins - it's a lowest-common-denominator solution that is tailored to webhosting companies.

If you want true virtualization, look into something like KVM, VMware ESXi, Xen, etc.

  • Ok, thanks. I think it's still helpful in isolating the clients against one another. What happens if there are different versions of a package installed in different containers? Do their processes coexist on the host peacefully? – BeBuschka Apr 28 '15 at 16:03
  • @BeBuschka yes. Different version will live happily together, as long as they are not compiled for different kernel versions, because as EEAA wrote above, only one kernel is running. Think of OpenVZ as a kind of hacky chroot container. – Craig Watson Apr 28 '15 at 16:19
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Think about OpenVZ is not a fully virtualization solution but a container virtualization one http://en.wikipedia.org/wiki/OpenVZ#OpenVZ_compared_to_other_virtualization_technologies. Its aim is to run lightweiht virtual servers with less overhead than an hypervisor.

The processes are fully separated from different OS instances (Guests) but the Host itself is a special one. You can think (simplifying really a lot) of OpenVZ as a sort of advanced chroot, rather than an alternative to VMWare, Virtualbox or Xen.

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