The command that controls a lot of automation that comes with VirtualBox software is called: vboxmanage. This article show how to use it in Centos/RHEL to automatically start your VM on boot.

First run:

vboxmanage list vms

This will list the names of all VMs you have.

If you have many VMs and want to list just the one you're currently running, use:

vboxmanage list runningvms

Capture the name of your VM.

Following is the command to start VM of your choice from the Linux shell, in a headless state:

vboxmanage startvm NAMEOFYOURVM --type headless

Result from the terminal would look something like this:

Now you can create your own SH script to run your VM on boot.

Btw. command to shutdown VM is this:

VBoxManage controlvm NAMEOFYOURVM savestate

This will stop your VM by "hibernating" it. This is a recommended way of turning off the VM machine, as hibernating prevents the data loss.