pty(7)                     DG/UX 4.30                      pty(7)



     NAME
          pty, pts, ptc - pseudo-terminal master/slave pseudo-device
          pair

     DESCRIPTION
          A pseudo-terminal (pty) is a pair of character devices, a
          master device and a slave device.  The master device is
          supported by the ptc driver and the slave device is
          supported by the pts driver.

          The slave device provides processes a standard tty interface
          as described in termio(7) and tty(7).  However, whereas
          other devices which provide the tty interface have a
          hardware device of some sort behind them, the slave device
          has, instead, another process manipulating it through the
          master half of the pseudo terminal.  That is, anything
          written on the master device is given to the slave device as
          input and anything written on the slave device is presented
          as input on the master device.

          The following ioctl calls apply only to pseudo terminals:

          TIOCSTOP
               Stops output to a terminal (e.g. like typing <Ctrl-S).
               Takes no parameter.

          TIOCSTART
               Restarts output (stopped by TIOCSTOP or by typing
               <Ctrl-S>).  Takes no parameter.

          TIOCPKT
               Enable/disable packet mode.  The ioctl parameter is the
               address of an int, whose value determines whether
               packet mode is to be enabled (non-zero value) or
               disabled (zero value).  When applied to the master side
               of a pseudo terminal, each subsequent read from the
               terminal will return data written on the slave part of
               the pseudo terminal preceded by a zero byte
               (symbolically defined as TIOCPKT_DATA), or a single
               byte reflecting control status information.  In the
               latter case, the byte is an inclusive-or of zero or
               more of the bits:

          TIOCPKT_FLUSHREAD
               whenever the read queue for the terminal is flushed.

          TIOCPKT_FLUSHWRITE
               whenever the write queue for the terminal is flushed.

          TIOCPKT_STOP
               whenever output to the terminal is stopped with <Ctrl-
               S>.



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     pty(7)                     DG/UX 4.30                      pty(7)



          TIOCPKT_START
               whenever output to the terminal is restarted.

          TIOCPKT_DOSTOP
               whenever t_stopc is <Ctrl-C> and t_startc is <Ctrl-Q>.

          TIOCPKT_NOSTOP
               whenever the start and stop characters are not <Ctrl-
               S/Ctrl-^Q>.

               While this mode is in use, the presence of control
               status information to be read from the master side may
               be detected by a select for exceptional conditions.

          TIOCUCNTL
               Enable/disable a mode that allows a small number of
               simple user ioctl commands to be passed through the
               pseudo-terminal, using a protocol similar to that of
               TIOCPKT.  The TIOCUCNTL and TIOCPKT modes are mutually
               exclusive.  This mode is enabled from the master side
               of a pseudo terminal by specifying (by reference) a
               nonzero parameter and disabled by specifying (by
               reference) a zero parameter.  Each subsequent read from
               the master side will return data written on the slave
               part of the pseudo terminal preceded by a zero byte, or
               a single byte reflecting a user control operation on
               the slave side.  A user control command consists of a
               special ioctl operation with no data; the command is
               given as UIOCCMD(n), where n is a number in the range
               1-255.  The operation value n will be received as a
               single byte on the next read from the master side.  The
               ioctl UIOCCMD(0) is a no-op that may be used to probe
               for the existence of this facility.  As with TIOCPKT
               mode, command operations may be detected with a select
               for exceptional conditions.

          TIOCREMOTE
               A mode for the master half of a pseudo terminal,
               independent of TIOCPKT.  This mode causes input to the
               pseudo terminal to be flow controlled and not input
               edited (regardless of the terminal mode).  Each write
               to the control terminal produces a record boundary for
               the process reading the terminal.  In normal usage, a
               write of data is like the data typed as a line on the
               terminal; a write of 0 bytes is like typing an end-of-
               file character.  TIOCREMOTE can be used when doing
               remote line editing in a window manager, or whenever
               flow controlled input is required.

          TIOCCONS
               Enable/disable console output redirection.  This
               slave-side ioctl call causes all output to /dev/syscon



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     pty(7)                     DG/UX 4.30                      pty(7)



               to go to the pty output instead.  Note that input is
               not redirected.  The command parameter is the address
               of an integer.  If this integer is zero, the call
               cancels redirection; if non-zero, it establishes
               redirection.

     FILES
          /dev/ttyp* /dev/ptyp*

     SEE ALSO
          termio(7), tty(7)












































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