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TTY_IOCTL(4)               Linux Programmer's Manual              TTY_IOCTL(4)



NAME
       tty ioctl - ioctls for terminals and serial lines

SYNOPSIS
       #include <&lt;termios.h>&gt;

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


DESCRIPTION
       The  ioctl()  call for terminals and serial ports accepts many possible
       command arguments.  Most require a third  argument,  of  varying  type,
       here called argp or arg.

       Use  of  ioctl makes for non-portable programs. Use the POSIX interface
       described in termios(3) whenever possible.


   Get and Set Terminal Attributes
       TCGETS    struct termios *argp
              Equivalent to tcgetattr(fd, argp).
              Get the current serial port settings.

       TCSETS    const struct termios *argp
              Equivalent to tcsetattr(fd, TCSANOW, argp).
              Set the current serial port settings.

       TCSETSW   const struct termios *argp
              Equivalent to tcsetattr(fd, TCSADRAIN, argp).
              Allow the output buffer to drain, and  set  the  current  serial
              port settings.

       TCSETSF   const struct termios *argp
              Equivalent to tcsetattr(fd, TCSAFLUSH, argp).
              Allow the output buffer to drain, discard pending input, and set
              the current serial port settings.

       The following four  ioctls  are  just  like  TCGETS,  TCSETS,  TCSETSW,
       TCSETSF,  except  that  they take a struct termio * instead of a struct
       termios *.

       TCGETA    struct termio *argp

       TCSETA    const struct termio *argp

       TCSETAW   const struct termio *argp

       TCSETAF   const struct termio *argp


   Locking the termios structure
       The termios structure of a tty can be locked.  The  lock  is  itself  a
       termios  structure,  with  nonzero  bits  or fields indicating a locked
       value.

       TIOCGLCKTRMIOS struct termios *argp
              Gets the locking status of the termios structure of  the  termi-
              nal.

       TIOCSLCKTRMIOS const struct termios *argp
              Sets  the  locking status of the termios structure of the termi-
              nal. Only root can do this.


   Get and Set Window Size
       Window sizes are kept in the kernel, but not used by the kernel (except
       in  the case of virtual consoles, where the kernel will update the win-
       dow size when the size of the virtual console changes, e.g. by  loading
       a new font).

       TIOCGWINSZ     struct winsize *argp
              Get window size.

       TIOCSWINSZ     const struct winsize *argp
              Set window size.

       The struct used by these ioctls is defined as

       struct winsize {
               unsigned short ws_row;
               unsigned short ws_col;
               unsigned short ws_xpixel;   /* unused */
               unsigned short ws_ypixel;   /* unused */
       };

       When  the  window  size changes, a SIGWINCH signal is sent to the fore-
       ground process group.


   Sending a Break
       TCSBRK    int arg
              Equivalent to tcsendbreak(fd, arg).
              If the terminal is using asynchronous serial data  transmission,
              and  arg  is zero, then send a break (a stream of zero bits) for
              between 0.25 and 0.5 seconds. If the terminal is not using asyn-
              chronous  serial data transmission, then either a break is sent,
              or the function returns without doing  anything.   When  arg  is
              nonzero, nobody knows what will happen.

              (SVR4,  UnixWare,  Solaris, Linux treat tcsendbreak(fd,arg) with
              nonzero arg like tcdrain(fd).  SunOS treats arg as a multiplier,
              and  sends  a  stream of bits arg times as long as done for zero
              arg.  DG-UX and AIX treat arg (when nonzero) as  a  timeinterval
              measured in milliseconds.  HP-UX ignores arg.)

       TCSBRKP   int arg
              So-called  "POSIX version" of TCSBRK. It treats nonzero arg as a
              timeinterval measured in deciseconds, and does nothing when  the
              driver does not support breaks.

       TIOCSBRK  void
              Turn break on, that is, start sending zero bits.

       TIOCCBRK  void
              Turn break off, that is, stop sending zero bits.


   Software flow control
       TCXONC    int arg
              Equivalent to tcflow(fd, arg).
              See  tcflow(3)  for  the  argument values TCOOFF, TCOON, TCIOFF,
              TCION.


   Buffer count and flushing
       FIONREAD  int *argp
              Get the number of bytes in the input buffer.

       TIOCINQ   int *argp
              Same as FIONREAD.

       TIOCOUTQ  int *argp
              Get the number of bytes in the output buffer.

       TCFLSH    int arg
              Equivalent to tcflush(fd, arg).
              See tcflush(3)  for  the  argument  values  TCIFLUSH,  TCOFLUSH,
              TCIOFLUSH.


   Faking input
       TIOCSTI   const char *argp
              Insert the given byte in the input queue.


   Redirecting console output
       TIOCCONS  void
              Redirect   output  that  would  have  gone  to  /dev/console  or
              /dev/tty0 to the given tty. If that was a pty master, send it to
              the  slave.   Anybody  can do this as long as the output was not
              redirected yet.  If it was redirected already EBUSY is returned,
              but root may stop redirection by using this ioctl with fd point-
              ing at /dev/console or /dev/tty0.


   Controlling tty
       TIOCSCTTY int arg
              Make the given tty the controlling tty of the  current  process.
              The current process must be a session leader and not have a con-
              trolling tty already. If this tty is already the controlling tty
              of  a  different  session group then the ioctl fails with EPERM,
              unless the caller is root and arg equals 1, in  which  case  the
              tty  is stolen, and all processes that had it as controlling tty
              lose it.

       TIOCNOTTY void
              If the given tty was the controlling tty of the current process,
              give up this controlling tty. If the process was session leader,
              then send SIGHUP and SIGCONT to the foreground process group and
              all processes in the current session lose their controlling tty.


   Process group and session ID
       TIOCGPGRP pid_t *argp
              When successful, equivalent to *argp = tcgetpgrp(fd).
              Get  the process group ID of the foreground proces group on this
              tty.

       TIOCSPGRP const pid_t *argp
              Equivalent to tcsetpgrp(fd, *argp).
              Set the foreground process group id of this tty.

       TIOCGSID  pid_t *argp
              Get the session ID of the given tty. This will fail with  ENOTTY
              in case the tty is not a master pty and not our controlling tty.
              Strange.


   Exclusive mode
       TIOCEXCL  void
              Put the tty into exclusive mode.  No further open(2)  operations
              on  the  terminal  are  permitted.   (They will fail with EBUSY,
              except for root.)

       TIOCNXCL  void
              Disable exclusive mode.


   Line discipline
       TIOCGETD  int *argp
              Get the line discipline of the tty.

       TIOCSETD  const int *argp
              Set the line discipline of the tty.


   Pseudo-tty ioctls
       TIOCPKT   const int *argp
              Enable (when *argp is nonzero) or disable packet mode.   Can  be
              applied  to the master side of a pseudotty only (and will return
              ENOTTY otherwise). In packet mode, each subsequent read(2)  will
              return  a  packet  that either contains a single nonzero control
              byte, or has a single zero byte followed by data written on  the
              slave  side  of  the  pty. If the first byte is not TIOCPKT_DATA
              (0), it is an OR of one or more of the following bits:

              TIOCPKT_FLUSHREAD   The read queue for the terminal is flushed.
              TIOCPKT_FLUSHWRITE  The write queue for the terminal is flushed.
              TIOCPKT_STOP        Output to the terminal is stopped.
              TIOCPKT_START       Output to the terminal is restarted.
              TIOCPKT_DOSTOP      t_stopc is `^S' and t_startc is `^Q'.
              TIOCPKT_NOSTOP      the start and stop characters are not `^S/^Q'.

              While this mode is in use, the presence of control status infor-
              mation  to  be  read  from  the master side may be detected by a
              select(2) for exceptional conditions.

              This mode is used by rlogin(1) and  rlogind(8)  to  implement  a
              remote-echoed, locally `^S/^Q' flow-controlled remote login.

              The  BSD  ioctls TIOCSTOP, TIOCSTART, TIOCUCNTL, TIOCREMOTE have
              not been implemented under Linux.


   Modem control
       TIOCMGET  int *argp
              get the status of modem bits.

       TIOCMSET  const int *argp
              set the status of modem bits.

       TIOCMBIC  const int *argp
              clear the indicated modem bits.

       TIOCMBIS  const int *argp
              set the indicated modem bits.

       Bits used by these four ioctls:

       TIOCM_LE        DSR (data set ready/line enable)
       TIOCM_DTR       DTR (data terminal ready)
       TIOCM_RTS       RTS (request to send)
       TIOCM_ST        Secondary TXD (transmit)
       TIOCM_SR        Secondary RXD (receive)
       TIOCM_CTS       CTS (clear to send)
       TIOCM_CAR       DCD (data carrier detect)
       TIOCM_CD         see TIOCM_CAR
       TIOCM_RNG       RNG (ring)
       TIOCM_RI         see TIOCM_RNG
       TIOCM_DSR       DSR (data set ready)


   Marking a line as local
       TIOCGSOFTCAR   int *argp
              ("Get software carrier flag") Get the status of the CLOCAL  flag
              in the c_cflag field of the termios structure.

       TIOCSSOFTCAR   const int *argp
              ("Set software carrier flag") Set the CLOCAL flag in the termios
              structure when *argp is nonzero, and clear it otherwise.

       If the CLOCAL flag for a line is off, the hardware carrier detect (DCD)
       signal  is  significant,  and  an open(2) of the corresponding tty will
       block until DCD is asserted, unless the O_NONBLOCK flag is  given.   If
       CLOCAL  is  set,  the  line  behaves as if DCD is always asserted.  The
       software carrier flag is usually turned on for local  devices,  and  is
       off for lines with modems.


   Linux specific
       For the TIOCLINUX ioctl, see console_ioctl(4).


   Kernel debugging
       #include <&lt;linux/tty.h>&gt;


       TIOCTTYGSTRUCT struct tty_struct *argp
              Get the tty_struct corresponding to fd.


RETURN VALUE
       The  ioctl()  system  call returns 0 on success. On error it returns -1
       and sets errno appropriately.


ERRORS
       ENOIOCTLCMD
              Unknown command.

       EINVAL Invalid command parameter.

       EPERM  Insufficient permission.

       ENOTTY Inappropriate fd.

EXAMPLE
       Check the condition of DTR on the serial port.

       #include <termios.h>
       #include <fcntl.h>
       #include <sys/ioctl.h>

       main() {
           int fd, serial;

           fd = open("/dev/ttyS0", O_RDONLY);
           ioctl(fd, TIOCMGET, &serial);
           if (serial & TIOCM_DTR)
               puts("TIOCM_DTR is not set");
           else
               puts("TIOCM_DTR is set");
           close(fd);
       }


SEE ALSO
       ioctl(2), termios(3), console_ioctl(4)




Linux                             2002-12-29                      TTY_IOCTL(4)