PTY(4)                               BSD                                PTY(4)



NAME
     pty - pseudo terminal driver

SYNOPSIS
     pseudo-device pty [ count ]

DESCRIPTION
     The pty driver provides support for a device-pair termed a pseudo
     terminal.  A pseudo terminal is a pair of character devices, a "master"
     device and a "slave" device. The slave device provides processes an
     interface identical to that described in tty(4).  However, whereas all
     other devices which provide the interface described in tty(4) 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.

     Use the program /etc/crpty to create pty pairs (see crpty(8)).  If
     invoked with no optional "count," 16 pseudo terminal pairs are
     configured.

     The following ioctl calls apply only to pseudo terminals:

     TIOCSTOP
          Stops output to a terminal (for example like typing ^S). Takes no
          parameter.

     TIOCSTART
          Restarts output (stopped by TIOCSTOP or by typing ^S).  Takes no
          parameter.

     TIOCPKT
          Enable/disable "packet" mode. Packet mode is enabled by specifying
          (by reference) a nonzero parameter and disabled by specifying (by
          reference) a zero parameter. 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 as with a ^S.

          TIOCPKT_START
               whenever output to the terminal is restarted.

          TIOCPKT_DOSTOP
               whenever t_stopc is ^S and t_startc is ^Q.

          TIOCPKT_NOSTOP
               whenever the start and stop characters are not ^S/^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.

          This mode is used by rlogin(1C) and rlogind(8C) to implement a
          remote-echoed, locally ^S/^Q flow-controlled remote login with
          proper back-flushing of output; it can be used by other similar
          programs.

     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.

SEE ALSO
     ioctl(2), rlogin(1C), read(2), write(2), tty(4), crpty(8), rlogind(8C)

FILES
     /dev/ptyp[0-f] master pseudo terminals
     /dev/ttyp[0-f] slave pseudo terminals

DIAGNOSTICS
     None.