Proper way to detach from control terminal?

[Guy Harris]

>	/*
>	 * TIOCNOTTY will get rid of my tty & set my pgrp to 0
>	 */
>	ioctl(0, TIOCNOTTY, 0);

RU sure?  I think TIOCNOTTY only works on "/dev/tty" - it's caught not
by the standard line discipline, say, but by the "/dev/tty" driver.

>The problem comes when you don't want a ctty but you do want to talk to a tty.
>Open() has the unfortunate side effect of handing out cttys' even when you
>don't want one.  You can do the following in the specified environment:

Note that you have to do those operations *after* you've opened the tty
in question, and gotten it as a controlling tty; doing it before won't
help. 

>POSIX:
>	Do a setsid().

Or use the O_NOCTTY flag when opening the tty, which prevents "open"
from making it a controlling tty in the first place.