My virtual machine is called centos.
$ vboxmanage list vms
$ vboxmanage startvm centos --type headless
$ vboxmanage snapshot centos list
Stop the machine if it's running, then restore a snapshot identified
either by its name or its ID. You can get both from issuing
vboxmanage snapshot centos list:
$ vboxmanage controlvm centos poweroff
$ vboxmanage snapshot centos restore a927529c-60fd-47c2-af98-4a0d38eea642