Prevent an upstart / lightdm / gdm service from running at boot on Ubuntu

You can use an override:

    sudo echo "manual" >> /etc/init/lightdm.override  

To start lightdm on command:

    sudo start lightdm  

To restore your system so that lightdm is always started on boot:

    sudo rm /etc/init/lightdm.override  

For more information, the upstart cookbook is your friend:

• http://upstart.ubuntu.com/cookbook/