Most Linux systems have what is called a default runlevel. It goes from 1 to 6.
Typically, runlevel 3 means headless. This is the recommendation for Amahi, if you are not going to use the desktop. This is done to conserve resources, because runlevel 3 does not start graphics (X windows and window managers, etc.), and frees memory and CPU.
The typical default is runlevel 5, which does start X as a service.
How to change the runlevel
You can set the default runlevel in
For runlevel 3, it should have a line like this
That means the system is running at runlevel 3 when it reboots next.