pty(4)                                                           pty(4)

  pty

  NAME

    pty, ptmx - pseudo terminal driver

  DESCRIPTION

    The pty(4) 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 subordinate (slave) device. The subordinate device provides
    to a process an interface identical to that described in tty(4). Where all
    other devices that provide the interface described in tty(4) have a
    hardware device of some sort behind them, the subordinate device has,
    another process instead that manipulates it through the master half of the
    pseudo terminal. That is, anything written on the master device is given
    to the subordinate device as input and anything written on the subordinate
    device is presented as input on the master device.

    INTERIX is configured with 256 pseudo terminals.

    The quick way to open a master pseudo terminal is to use open(2) with a
    path of /dev/ptmx. The name of the subordinate side can found with
    ptsname(2) or ptsname_r(2).

    The following ioctl(2) calls apply only to pseudo terminals:

    TIOCSTOP
        Stops output to a terminal (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 is 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 subordinate 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 or emptied.

        TIOCPKT_FLUSHWRITE
            Whenever the write queue for the terminal is flushed or emptied.

        TIOCPKT_STOP
            Whenever output to the terminal is stopped by using ^S.

        TIOCPKT_START
            Whenever output to the terminal is restarted.

        TIOCPKT_DOSTOP
            Whenever c_cc[VSTART] is ^S and c_cc[VSTOP] 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 can be detected by a
            select(2) for exceptional conditions.

        TIOCPKT_IOCTL
            Whenever one of the members of the termios structure for the
            terminal changes. Only the new content of the termios structure is
            returned. Other TIOCPKT control information (except for
            TIOCPKT_DATA) can be combined using the exclusive-OR operation
            with this control bit. A select(2) on the master side of the
            terminal will return true for read, in addition to exception.
            While in packet mode, if a read(2) request is for fewer than
            sizeof(struct termios) +1 bytes and TIOCPKT_IOCTL control
            information is available, the TIOCPKT_IOCTL information will
            remain pending until a sufficiently large read(2) request is
            performed. All other packet mode control bits will be delivered,
            and select(2) will continue to return true for read and exception
            until the TIOCPKT_IOCTL information is retrieved.

    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 subordinate part
        of the pseudo terminal preceded by a zero byte, or a single byte
        reflecting a user control operation on the subordinate side. A user
        control command consists of a special ioctl() operation with no data;
        the command is given as UIOCCMD 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 is a no-op that
        can be used to probe for the existence of this facility. As with
        TIOCPKT mode, command operations can be detected with a select() for
        exceptional conditions.

    TIOCREMOTE
        A mode for the master half of a pseudo terminal, independent of
        TIOCPKT. This is not enabled in the current version of Interix. This
        mode causes input to the pseudo terminal to be flow controlled and not
        input edited (regardless of the terminal mode). Each write operation
        to the control terminal produces a record boundary for the process
        reading the terminal. In normal usage, a write operation 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.

  FILES

    /dev/pty[p-zA-E][0-9a-f]
    /dev/ptmx
        Master pseudo terminals

    /dev/tty[p-zA-E][0-9a-f]
        Subordinate (slave) pseudo terminals

  SEE ALSO

    ioctl(2)

    termios(4)

    tty(4)