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       tty - controlling terminal


       The  file  /dev/tty  is  a character file with major number 5 and minor
       number 0, usually of mode 0666  and  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.

       Detach the calling 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(2)  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.




       chown(1),  mknod(1),  ioctl(2),  termios(3),  console(4), tty_ioctl(4),
       ttyS(4), agetty(8), mingetty(8)


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