OpenVZ supports VM guest initialization via cloud-init, so you can perform some of the initial configuration tasks described further in this section on stopped virtual machines. The supported tasks are: mounting the guest tools image, setting user names and passwords, and configuring network settings.
The changes resulting from performing the above tasks are not applied to the VM immediately but rather saved as instructions to be carried out when the guest OS with cloud-init is loading. So when you run a corresponding command (e.g., prlctl set --userpasswd), the following happens: the bundled image with cloud-init instructions is copied to the VM home path, a CD-ROM device is added to the VM, and the image is mounted to said CD-ROM. However, the changes (e.g., to the user name and password) will only be applied after you install and start loading the guest OS.
As mentioned above, you will need cloud-init installed in a guest OS for the feature to work. For Linux guests, the easiest way to get cloud-init is to install a "cloud-enabled" distribution that already comes with it. You can also install cloud-init manually (e.g., by running yum install cloud-init on CentOS 7). For Windows guests, you can create your own distributions with cloud-init or install it manually. The Windows version is available at https://cloudbase.it/cloudbase-init/.
