Articulos de referencia
[https://www.virtualbox.org/manual/ch09.html#autostart]

[http://www.vionblog.com/virtualbox-4-3-autostart-debian-wheezy/]

Before this autostart script the virtual machines ware started usually from rc.local, now you can do it with VirtualBox autostart config. Do the following to enable the autostart service:

As root:

vi /etc/default/virtualbox

add this lines:

VBOXAUTOSTART_DB=/etc/vbox
VBOXAUTOSTART_CONFIG=/etc/vbox/autostart.conf

Now change the permissions to the folder for vboxusers

chgrp vboxusers /etc/vbox
chmod 1775 /etc/vbox

Create the /etc/vbox/autostart.conf and add this users that you want autostart to be enabled, my users for running the virtual machines is vbox

vi /etc/vbox/autostart.conf

# Default policy is to deny starting a VM, the other option is "allow".
default_policy = deny

# user vbox is allowed to start virtual machines but starting them
# will be delayed for 10 seconds
vbox = {
 allow = true
 startup_delay = 10
}

Now login as vbox and enable autostart on the machines you want to start automatically, i will do  it for two machines called VirtualMachine1 and VirtualMachine2

VBoxManage setproperty autostartdbpath /etc/vbox
VBoxManage modifyvm VirtualMachine1 --autostart-enabled on
VBoxManage modifyvm VirtualMachine2 --autostart-enabled on

Now, as root run this command, or reboot your server:

/etc/init.d/vboxautostart-service start