You can cause a virtual machine to execute its shutdown sequence, as if you'd pressed its power button, by typing: (e.g. for a VM called 'matt1'):

$ bigv vm shutdown matt1

CD URL:              
CPUs:                4
Discs:               
Management address:  213.138.98.28
Name:                matt1
Network interfaces:  
Power on:            no
RAM (MB):            4000

Currently, the dump of various statistics shows that the shutdown signal was sent successfully.

Most sensibly-configured operating systems will react to the shutdown signal unconditionally, and should stop running within a minute or two after ensuring that they have tidied up before they exit.

It is possible, however, that nothing will happen, or that the VM will prompt you on its console for confirmation. If that's the case you may need to use vm connect to see what's going on and initiate a shutdown from within the system.

A shut down system will not start up again until you run vm start, and will be billed at the full rate for the duration it is stopped.