[BRLTTY] brlapi_enterTttyMode(BRLAPI_TTY_DEFAULT, buf) result in brlapi_error Can't determine tty number

[Quartel, Eric de]

Hello,

My developed software works well when i start it from command line.
The computer (a raspberry pi) had already booted.

But, when i want to start the program during boot (/etc/rc.local) I get the message that it can't determine the tty number.
This is after the brlapi_enterTttyMode(BRLAPI_TTY_DEFAULT,buf) buf is a string "Voyager".

What happens?
Can anybody please give me an answer or a way to get around this problem?

Kind regards,
Eric de Quartel