ioctl(2)                                                       ioctl(2)

  ioctl()

  NAME

    ioctl() - control a socket or file

  SYNOPSIS

    #include 
    #include 

    int ioctl (int fd, int command, ...);

  DESCRIPTION

    The ioctl(2) function manipulates the underlying device parameters. In
    particular, many operating characteristics of terminals and sockets may be
    controlled with ioctl(2) requests. The argument fd must be an open file
    descriptor.

    Encoded in an ioctl(2) request is whether the argument is an in parameter
    or an out parameter, and the size of the remaining arguments in bytes.

    The possible values for command are defined in  and include:

    FIONBIO
        Sets or clears on-blocking I/O. The arg should point to an int. If the
        int is non-zero, the flag is set and non-blocking mode is enabled; if
        it is zero, the flag is cleared, and non-blocking mode is disabled.

    FIONREAD
        Returns in arg the number of bytes available to read from fd; arg
        should point to an int.

    SIOCATMARK
        For sockets; this boolean returns true if the socket's read pointer is
        at the out-of-band mark.

    TIOCEXT
        For pseudo terminals only; when this flag is non-zero (on), external
        processing mode is enabled. When zero, external processing mode is
        disabled. External processing mode places the terminal in a mode where
        characters are never echoed, special characters are never processed,
        and no characters are erased. This mode is often used in programs like
        telnetd(1).

    TIOCSIG
        For pseudo terminals only; the arg should point to an int. Specifies a
        signal that can be applied to the terminal as if the signal were to be
        keyboard-generated. Valid signals are SIGTSTP, SIGINT, and SIGQUIT.

    The call

    ioctl(d, FIONBIO, NULL)

    is equivalent to a call to

    fcntl(d, F_SETFL, O_NONBLOCK)

    except that for each fcntl(2) call, all of the flag values must set, while
    the ioctl(2) call allows you to set only one flag.

  RETURN VALUE

    The return value of the ioctl(2) depends upon the command. If an error
    occurs, it returns -1 and sets errno to indicate the error.

  ERRORS

    The ioctl(2) call will fail if:

    [EAGAIN]
        A device opened for non-blocking i/o is not yet ready.

    [EBADF]
        Fd is not a valid open file descriptor.

    [EINTR]
        The function was interrupted by a signal.

    [EINVAL]
        the data to which arg points is not valid.

  NOTES

    Traditional implementations of ioctl(2) also handle the terminal
    interface. For terminal manipulation (traditionally handled with TIOCGETD,
    TIOCSETD, TIOCGETP, and TIOCSETP or with stty() and gtty()), use the POSIX
    calls tcgetattr(2), tcsetattr(2), cfgetispeed(3), cfsetispeed(3),
    cfgetospeed(3), and cfsetospeed(3) to manipulate the termios structure,
    instead.

  SEE ALSO

    execve(2)

    fcntl(2)

  USAGE NOTES

    The ioctl function is thread safe.

    The ioctl function is not async-signal safe.