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

       tty_ioctl - ioctls for terminals and serial lines

       #include <termios.h>

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

       The  ioctl(2) 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 nonportable 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 terminal can be locked.  The lock is	itself
       a  termios  structure,  with nonzero bits or fields indicating a locked

       TIOCGLCKTRMIOS struct termios *argp
	      Gets the locking status of the termios structure of  the	termi‐

       TIOCSLCKTRMIOS const struct termios *argp
	      Sets  the	 locking status of the termios structure of the termi‐
	      nal.   Only  root	 (more	 precisely:   a	  process   with   the
	      CAP_SYS_ADMIN capability) 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, for example, by
       loading a new font).

       The following constants and structure are defined in <sys/ioctl.h>.

       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
	      asynchronous 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 time interval
	      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,

   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,

   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 terminal.  If that was a pseudoterminal
	      master, send it to the slave.  In Linux before  version  2.6.10,
	      anybody  can  do	this  as long as the output was not redirected
	      yet; since  version  2.6.10,  only  root	(a  process  with  the
	      CAP_SYS_ADMIN capability) may do this.  If output was redirected
	      already EBUSY is returned, but redirection  can  be  stopped  by
	      using this ioctl with fd pointing at /dev/console or /dev/tty0.

   Controlling terminal
       TIOCSCTTY int arg
	      Make  the given terminal the controlling terminal of the calling
	      process.	The calling process must be a session leader  and  not
	      have  a  controlling  terminal  already.	 If  this  terminal is
	      already the controlling terminal of a  different	session	 group
	      then the ioctl fails with EPERM, unless the caller is root (more
	      precisely: has the CAP_SYS_ADMIN capability) and arg  equals  1,
	      in which case the terminal is stolen, and all processes that had
	      it as controlling terminal lose it.

       TIOCNOTTY void
	      If the given terminal was the controlling terminal of the	 call‐
	      ing  process, give up this controlling terminal.	If the process
	      was session leader, then send SIGHUP and SIGCONT	to  the	 fore‐
	      ground  process  group  and all processes in the current session
	      lose their controlling terminal.

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

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

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

   Exclusive mode
       TIOCEXCL	 void
	      Put the terminal into exclusive mode.  No further open(2) opera‐
	      tions on the terminal  are  permitted.   (They  will  fail  with
	      EBUSY,   except	for   root,   that  is,	 a  process  with  the
	      CAP_SYS_ADMIN capability.)

       TIOCNXCL	 void
	      Disable exclusive mode.

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

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

   Pseudoterminal ioctls
       TIOCPKT	 const int *argp
	      Enable (when *argp is nonzero) or disable packet mode.   Can  be
	      applied  to  the	master side of a pseudoterminal 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 byte containing zero (' ')
	      followed	by  data written on the slave side of the pseudotermi‐
	      nal.  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	  The start and stop characters are ^S/^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.

	      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  terminal
       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.

       For the TIOCLINUX ioctl, see console_ioctl(4).

   Kernel debugging
       #include <linux/tty.h>

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

       The ioctl(2) system call returns 0 on success.  On error it returns  -1
       and sets errno appropriately.

       EINVAL Invalid command parameter.

	      Unknown command.

       ENOTTY Inappropriate fd.

       EPERM  Insufficient permission.

       Check the condition of DTR on the serial port.

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

	   int fd, serial;

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

       ioctl(2), termios(3), console_ioctl(4), pty(7)

       This  page  is  part of release 3.53 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at

Linux				  2008-10-29			  TTY_IOCTL(4)

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