how to recognize guest hang from host?

[scottgus1]

I have two VM's (XP and SBS2003) on a XP host. Occasionally the VMs hang on a shutdown or restart. Meaning, they go through the entire shutdown process, including the "Windows is shutting down", "Closing Network settings", etc. boxes, and goes to the blue or gray log-off background color, then just sits there with no disk or network activity shown on the Virtualbox bottom status bar. I have searched and found that sound cards might be the cause, but I have a ICH AC97 card in the SBS2003 VM, and no sound card in the XP VM. Both occasionally hang on shutdown, so I'm not sure this is my problem.

Seeing as these hangs may be hard to diagnose, and I do a full shutdown of the VM's for a backup script each night, a hang like this holds up the backup process and leaves these VM's unavailable in the morning, and I have to manually restart them.

Is there any way for the host to tell when the guest has hung, give it a certain time to clear itself, and then kill the VM if it hasn't unhung? My backup script already goes through a loop waiting for the "Vboxmanage showvminfo [VMname]" to return "State Powered Off". shovminfo returns "State running" even whine the VM is in the shutting-down process. Is there something else I could look for to tell if the guest has hung?

[scottgus1]

I should say that I cracked out "Vboxmanage metrics" and figured out how to monitor the CPU/Load numbers. Next time I get a shutdown hang, I'll see what I get.

Meanwhile, does anyone have info on how to determine a hang from a host script of some sort?