tty(4)                                                           tty(4)

  tty

  NAME

    tty - general terminal interface

  SYNOPSIS

    #include 

  DESCRIPTION

    This section describes the interface to the terminal drivers in the
    system.

  Terminal special files

    Each terminal on the system usually has a terminal special device file
    associated with it in the directory /dev/ (for example, /dev/ttyn02). When
    a user logs into the system on one of these terminals, the system has
    already opened the associated device and prepared the line for normal
    interactive use. There is also a special case of a terminal file that
    connects not to a hardware terminal port, but to another program on the
    other side. These special terminal devices are called ptys and provide the
    mechanism necessary to give users the same interface to the system when
    logging in over a network (using telnet(1) for example.) Even in these
    cases the details of how the terminal file was opened and set up is
    already handled by special software in the system. Thus, users do not
    normally need to worry about the details of how these lines are opened or
    used.

    When an interactive user logs in, the system prepares the line to behave
    in a certain way (called a line discipline the particular details of which
    is described in stty(1) at the command level, and in termios(4) at the
    programming level. A user may be concerned with changing settings
    associated with his particular login terminal and should refer to the
    preceding man pages for the common cases. The remainder of this man page
    is concerned with describing details of using and controlling terminal
    devices at a low level, such as that possibly required by a program
    wishing to provide features similar to those provided by the system.

  Line disciplines

    A terminal file is used like any other file in the system in that it can
    be opened, read, and written to using standard system calls. For each
    existing terminal file, there is a software processing module called a
    line discipline is associated with it. The line discipline essentially
    glues the low level device driver code with the high level generic
    interface routines (such as read(2) and write(2)), and is responsible for
    implementing the semantics associated with the device. When a terminal
    file is first opened by a program, the default line discipline called the
    termios line discipline is associated with the file. This is the primary
    line discipline that is used in most cases and provides the semantics that
    users normally associate with a terminal. When the termios line discipline
    is in effect, the terminal file behaves and is operated according to the
    rules described in termios(4). Please refer to that man page for a full
    description of the terminal semantics. The operations described here
    generally represent features common across all line disciplines however
    some of these calls may not make sense in conjunction with a line
    discipline other than termios, and some may not be supported by the
    underlying hardware (or lack thereof, as in the case of ptys).

  Terminal file operations

    The majority of terminal settings can be handled through the tc family of
    interfaces. Termios(4) defines them as function calls, not ioctl(2)
    requests. The following section lists the available ioctl(2) requests. The
    name of the request, a description of its purpose, and the typed argp
    parameter (if any) are listed. For example, the first entry says

    TIOCGWINSZ

    and would be called on the terminal associated with file descriptor zero
    by the following code fragment:

    struct winsize ws;
    ioctl(0, TIOCGWINSZ, &ws);

  Terminal file request descriptions

    TIOCSETD intldisc
        Change to a new line discipline, indicated by ldisc. Line disciplines
        are define in ; currently only TTYDISC (termios
        interactive line discipline) is supported.
    TIOCGETD intldisc
        Get current line disciple in ldisc.
    TIOCSBRK void
        Set terminal hardware into BREAK condition.
    TIOCCBRK void
        Clear terminal hardware BREAK condition.
    TIOCSDTR void
        Assert data terminal ready (DTR).
    TIOCCDTR void
        Clear data terminal ready (DTR).
    TIOCSRTS void
        Assert request to send (RTS).
    TIOCCRTS void
        Clear request to send (RTS).
    TIOCGPGRP int *tpgrp
        Return current process group associated with the terminal in the
        integer pointed to by tpgrp.
    TIOCSPGRP int *tpgrp
        Associate terminal with process group number in the integer pointed to
        by tpgrp.
    TIOCGETA struct termios *term
        Place current value of termios state associated with device in the
        structure pointed to by term.
    TIOSGETA struct termios *term
        Immediately set termios state associated with device, using data in
        the structure pointed to by term.
    TIOSGETAW struct termios *term
        Wait for output to complete, then set termios state associated with
        device, using data in the structure pointed to by term.
    TIOSGETAF struct termios *term
        Wait for output to complete, clear pending input, then set termios
        state associated with device, using data in the structure pointed to
        by term.
    TIOSGETAR struct termios *term
        Clear pending input, then set termios state associated with device,
        using data in the structure pointed to by term.
    TIOCOUTQ int *num
        Place current number of bytes in the output queue in the integer
        pointed to by num.
    TIOCSTI char *cp
        Simulate typed input. Pretend the terminal received the character
        pointed to by cp.
    TIOCSTOP void
        Stop output on the terminal (like typing ^S at the keyboard).
    TIOCSTART void
        Start output on the terminal (like typing ^Q at the keyboard).
    TIOCSCTTY void
        Make the terminal the controlling terminal for the process (the
        process should not currently have a controlling terminal).
    TIOCDRAIN void
        Wait until all output is drained.
    TIOCEXCL void
        Set exclusive use on the terminal; no further opens are permitted.
    TIOCNXCL void
        Clear exclusive use on the terminal.
    TIOCFLUSH int *what
        Clear input or output queue, depending on value of integer pointed to
        by what. If the integer contains the FREAD bit defined in sys/file.h,
        the input queue is cleared. If it contains the FWRITE bit, the output
        queue is clear. If it is zero, both queues are cleared.
    TIOCGWINSZ struct winsize *ws
        Put the window size information associated with the terminal in the
        winsize structure pointed to by ws. The window size structure contains
        the number of rows and columns (and pixels if appropriate) of the
        devices attached to the terminal. It is set by user software and is
        the means by which most full-screen oriented programs determine the
        screen size. The winsize structure is defined in .
    TIOCSWINSZ struct winsize *ws
        Set the window size associated with the terminal to be the value in
        the winsize structure pointed to by ws (see above).
    TIOCCONS int *on
        Redirect kernel console output depending on the value of the integer
        pointed to by on. If it is non-zero, redirect kernel console output to
        this terminal; if it is zero, redirect kernel console output back to
        the normal console.
    TIOCMSET int *state
        The integer pointed to by state contains bits that correspond to modem
        states. this call sets the terminal modem state to that represented by
        state. The defined variables and modem states are:
        CM_DTR        Data Terminal Ready

        TIOCM_RTS     Request To Send

        TIOCM_CTS     Clear To Send

        TIOCM_CAR     Carrier Detect

        TIOCM_CD      Carrier Detect

        TIOCM_RNG     Ring Indication

        TIOCM_RI      Ring Indication

        TIOCM_DSR     Data Set Ready
    TIOCMGET int *state
        Return current state of the terminal modem lines; see TIOCMSET for a
        description of bits that can be set in state.
    TIOCMBIS int *state
        The bits in the integer pointed to by state represent modem state, but
        they are OR-ed with the current state.
    TIOCMBIC int *state
        The bits in the integer pointed to by state represent modem state, but
        each bit that is on in state is cleared in the terminal.

  SEE ALSO

    stty(1)

    fcntl(2)

    ioctl(2)

    tcgetattr(2)

    tcsetattr(2)

    pty(4)

    termios(4)