devtty(7)                  DG/UX 4.30                   devtty(7)



     NAME
          devtty - control terminal pseudo-device

     DESCRIPTION
          The file /dev/tty is, in each process, a synonym for the
          control terminal associated with that process.  The file is
          useful if you want a program to write messages on the
          terminal no matter how output has been redirected.  You can
          also use it when a program needs a filename for output and
          you do not want to find out which terminal is currently in
          use.

          If a process that has no control terminal opens a terminal
          file, the terminal becomes the control terminal for that
          process.  The control terminal is thereafter inherited by a
          child process during a fork(2) system call, even if the
          control terminal is closed.

          All operations on /dev/tty behave like operations on the
          actual control terminal special file (/dev/tty*), except for
          the special ioctl TIOCNOTTY, which is recognized only on the
          /dev/tty device:

                    ioctl(fildes, TIOCNOTTY, 0);

          TIOCNOTTY breaks the association of a process with its
          control terminal, and also sets the process group of the
          calling process to the process id of that process.  Further
          I/O requests to the file will fail with the external
          variable errno set to ENXIO.  Subsequent opens of /dev/tty
          will also fail with errno set to ENXIO.

     FILES
          /dev/tty

     SEE ALSO
          termio(7), tty(7).


















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