tty(4) -- Linux man page
NAMEtty - controlling terminal
DESCRIPTIONThe file /dev/tty is a character file with major number 5 and minor number 0, usually of mode 0666 and owner.group root.tty. It is a synonym for the controlling terminal of a process, if any.
TIOCNOTTYDetach the current process from its controlling terminal.
If the process is the session leader, then SIGHUP and SIGCONT signals are sent to the foreground process group and all processes in the current session lose their controlling tty.
This ioctl() call only works on file descriptors connected to /dev/tty. It is used by daemon processes when they are invoked by a user at a terminal. The process attempts to open /dev/tty. If the open succeeds, it detaches itself from the terminal by using TIOCNOTTY, while if the open fails, it is obviously not attached to a terminal and does not need to detach itself.
SEE ALSOmknod(1), chown(1), getty(1), ioctl(2), termios(3), console(4), ttys(4)