man > tty(4)

tty(4)                                Kernel Interfaces Manual                                tty(4)

NAME
       tty - controlling terminal

DESCRIPTION
       The  file  /dev/tty  is a character file with major number 5 and minor number 0, usually with
       mode 0666 and ownership root:tty.  It is a synonym for the controlling terminal of a process,
       if any.

       In addition to the ioctl(2) requests supported by the device that tty refers to, the ioctl(2)
       request TIOCNOTTY is supported.

   TIOCNOTTY
       Detach the calling process from its controlling terminal.

       If the process is the session leader, then SIGHUP and SIGCONT signals are sent to  the  fore‐
       ground process group and all processes in the current session lose their controlling tty.

       This  ioctl(2) call works only on file descriptors connected to /dev/tty.  It is used by dae‐
       mon 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  de‐
       tach itself.

FILES
       /dev/tty

SEE ALSO
       chown(1),  mknod(1),  ioctl(2),  ioctl_console(2), ioctl_tty(2), termios(3), ttyS(4), vcs(4),
       pty(7), agetty(8), mingetty(8)

Linux man-pages 6.7                          2023-10-31                                       tty(4)