This is a fairly simply cron which will create snapshots for all running virtualbox guest VMS, for all user accounts on the system with home directories in /home. It is not needed to back up stopped VMs because (a) they don't change and (b), normal file system backups of the images will result in consistent images which can be restarted.
Assuming you need this because you are using Virtualbox, simply drop the script into /etc/cron.daily.