@fossfreedom I didn't pay attention to the fact it was closed, my bad. Let's say it wasn't closed, are you saying we should reject edits that only improves readability?
To simulate cron's environment run: "sudo su -", "su - seths", "vboxmanage list runningvms", if it fails run "DISPLAY=:0.0" and try "vboxmanage list runningvms" again.
It depends on how vboxmanage comunicates with the virtual machines. I used vboxmanage once, and I had to run it with the same user that runs the vm. You can test it yourself. Become root and try to run some command on a VM.
The cron service runs as root, and root can impersonate any user. For example, run "sudo su -" to become root, you'll have to enter your password. Then run "su - seths", root will become seths without asking for password.
You'll have to put username after the *'s. Like: 0 3 * * * root vboxmanage controlvm virtualpbx acpipowerbutton. Use the same user that runs the virtual machines.