The memory ballooning service, formerly known as VBoxBalloonCtrl, was renamed to VBoxWatchdog. This service now incorporates the following host services that are meant to be run in a server environment:

• Memory ballooning control. This service automatically takes care of a VM's configured memory balloon. See Memory Ballooning. This service is useful for server environments where VMs may dynamically require more or less memory during runtime.

  The service periodically checks a VM's current memory balloon and its free guest RAM and automatically adjusts the current memory balloon by inflating or deflating it accordingly. This handling only applies to running VMs having recent Guest Additions installed.

• Host isolation detection. This service provides a way to detect whether the host cannot reach the specific server instance anymore and take appropriate actions, such as shutting down, saving the current state or even powering down certain VMs.

All configuration values can be either specified using the command line or global extradata, whereas command line values always have a higher priority when set. Some of the configuration values also be specified on a per-VM basis. So the overall lookup order is: command line, per-VM basis extradata if available, global extradata.