boot-args, setting a default user, and empty password



I post a message some weeks ago. One told me to try nvram boot-args="-v". It was perfect to solve my problem.

But now I would like to know if anybody can list me the differents arguments it exists. I see there was -s to start as single user. I know -v to set verbose starting up, but no one else.

But my purpose is a little bite different because it happends later in the system starting up : I would like to set a default user. Example : there are four users {Root, Admin, Child, Guest}. I want the MacOS X to start with Child account by default. So if I want to log as Admin I will have to log out (opening by this way the Loggin window that didn't appear at start up), and to type "Admin" log and the right Password.

Can you help me ?

One thing else : do you know a way to dissable passwords ? I mean : is it possible to enter empty ( "" ) as password ?

Thank you very much,
Pierre Grabolosa.
you can control which user gets logged in automatically in the system preferences, users control panel