Why is Virtualbox start mode not detachable by default

Question

Virtualbox has three start modes:

• normal (with a window for the VM but window cannot be closed)
• headless start (no window for the VM, but you can see a screenshot in VBox UI)
• detachable start (a mix of the above two; window can be closed without turning off VM)

I was wondering, why do they have these three options when the third one satisfies the first and second? Is it possible there are also performance reasons?

In other words, why should I ever need to use the other options?

Answer 1

You can read why in the current version of the user manual for the startvm command:

Starts a VM with detachable UI (technically it is a headless VM with user interface in a separate process). This is an experimental feature as it lacks certain functionality at the moment (e.g. 3D acceleration will not work).

So, yes, this is still a new feature and it is missing some of the features a fully attached GUI provides.

Answer 2

The global or per-VM default value for the VM front end type will be taken if the type is not explicitly specified. If none of these are set, the GUI variant will be started.

The following values are allowed:

gui
Starts a VM showing a GUI window. This is the default.

headless
Starts a VM without a window for remote display only.

separate
Starts a VM with a detachable UI. Technically, it is a headless VM with user interface in a separate process. This is an experimental feature as it lacks certain functionality, such as 3D acceleration.