vSphere 5.1 introduces the vCenter Single Sign On service as part of the vCenter Server management infrastructure. This change affects vCenter Server installation, upgrading, and operation. As part of this change, vCenter Inventory Service is now installed separately from vCenter Server.

When you install or upgrade vCenter Server 5.1, you must install vCenter Single Sign On and install or upgrade vCenter Inventory Service, in that order, before you install or upgrade vCenter Server.

IMPORTANT VMware does not support command‐line installation and upgrade methods for vCenter Server. However, if the installation or upgrade succeeds, VMware supports the installed or upgraded product.