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One of the most important, yet least visible, functions of the VMware Tools Service is to send regular ''heartbeat'' messages to VMware Server so that it can detect (via the lack of heartbeats) when a particular virtual machine, or its respective guest operating system, has failed.
Another responsibility of VMware Tools Service involves the handling of communication between the guest and host operating systems. It is not too unrealistic to make the statement that none of today's popular operating systems have been written specifically to run within a VMware Server virtual machine. As such, none of these guest operating systems are designed to accept and respond to any form of communication from the VMware Server environment. Whilst this isn't generally problem, an issue arises when we consider that the VI Web Access management interface provides the ability to power off, restart and suspend guest operating systems at the press of a tool bar button or menu option, avoiding the need to open a VMware Remote Console session, log into the guest operating system and perform an orderly shutdown or reboot. Since there is no mechanism built into most operating systems that would allow VMware Server to request a clean shutdown or restart, this functionality is instead provided by the VMware Tools Service. When a user, for example, restarts a virtual machine from the VI Web Access management interface, VMware Server notifies the VMware Tools Service running on the guest operating system, which in turn executes the commands necessary to perform a clean and orderly shutdown or restart. In addition, VMware Tools Service also provides a mechanism for administrators to configure custom scripts to be executed within the guest operating system when the power state of the underlying virtual machine changes. This particular topic is covered in greater detail in the [[Working with VMware Tools Scripts and Power States]] chapter of this book.
In another example of communication between host and guest operating systems, VMware Tools Service is also responsible for ensuring that the system time of the host and guest operating systems are synchronized.