IOCTL_TTY(2)                                                 Linux Programmer's Manual                                                IOCTL_TTY(2)

NAME

       ioctl_tty - ioctls for terminals and serial lines

SYNOPSIS

       #include <termios.h>

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

DESCRIPTION

       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
       value.

       TIOCGLCKTRMIOS struct termios *argp
              Gets the locking status of the termios structure of the terminal.

       TIOCSLCKTRMIOS const struct termios *argp
              Sets the locking status of the termios structure of the terminal.  Only 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
       window 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 foreground 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, 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 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 a process with the CAP_SYS_ADMIN capability may do this.  If output was redirected already EBUSY is returned, but redi-
              rection 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.  For this case, arg should be specified as zero.

              If this terminal is already the controlling terminal of a different session group, then the ioctl fails with EPERM, unless the call-
              er  has  the  CAP_SYS_ADMIN capability and arg equals 1, in which case the terminal is stolen, and all processes that had it as con-
              trolling terminal lose it.

       TIOCNOTTY void
              If the given terminal was the controlling terminal of the calling process, give up this controlling terminal.  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 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 terminal.

       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 fails with the error ENOTTY if 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) operations on the terminal are permitted.  (They fail with EBUSY, except
              for a process with the CAP_SYS_ADMIN capability.)

       TIOCGEXCL int *argp
              (since Linux 3.8) If the terminal is currently in exclusive mode, place a nonzero value in the location pointed to by  argp;  other-
              wise, place zero in *argp.

       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 pseudoterminal.  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 information to be read from the master side may be detected by a select(2)
              for exceptional conditions or a poll(2) for the POLLPRI event.

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

       TIOCGPKT  const int *argp
              (since Linux 3.8) Return the current packet mode setting in the integer pointed to by argp.

       TIOCSPTLCK     int *argp
              Set (if *argp is nonzero) or remove (if *argp is zero) the pseudoterminal slave device.  (See also unlockpt(3).)

       TIOCGPTLCK     int *argp
              (since Linux 3.8) Place the current lock state of the pseudoterminal slave device in the location pointed to by argp.

       TIOCGPTPEER    int flags
              (since  Linux  4.13) Given a file descriptor in fd that refers to a pseudoterminal master, open (with the given open(2)-style flags)
              and return a new file descriptor that refers to the peer pseudoterminal slave device.  This operation can be performed regardless of
              whether the pathname of the slave device is accessible through the calling process's mount namespace.

              Security-conscious  programs  interacting  with  namespaces  may  wish  to  use this operation rather than open(2) with the pathname
              returned by ptsname(3), and similar library functions that have insecure APIs.  (For example, confusion  can  occur  in  some  cases
              using ptsname(3) with a pathname where a devpts filesystem has been mounted in a different mount namespace.)

       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.

       The following bits are used by the above 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)

       TIOCMIWAIT     int arg
              Wait  for  any of the 4 modem bits (DCD, RI, DSR, CTS) to change.  The bits of interest are specified as a bit mask in arg, by ORing
              together any of the bit values, TIOCM_RNG, TIOCM_DSR, TIOCM_CD, and TIOCM_CTS.  The caller should use TIOCGICOUNT to see  which  bit
              has changed.

       TIOCGICOUNT    struct serial_icounter_struct *argp
              Get  counts  of  input  serial  line interrupts (DCD, RI, DSR, CTS).  The counts are written to the serial_icounter_struct structure
              pointed to by argp.

              Note: both 1->0 and 0->1 transitions are counted, except for RI, where only 0->1 transitions are counted.

   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.

   Linux-specific
       For the TIOCLINUX ioctl, see ioctl_console(2).

   Kernel debugging
       #include <linux/tty.h>

       TIOCTTYGSTRUCT struct tty_struct *argp
              Get the tty_struct corresponding to fd.  This command was removed in Linux 2.5.67.

RETURN VALUE

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

ERRORS

       EINVAL Invalid command parameter.

       ENOIOCTLCMD
              Unknown command.

       ENOTTY Inappropriate fd.

       EPERM  Insufficient permission.

EXAMPLE

       Check the condition of DTR on the serial port.

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

       int
       main(void)
       {
           int fd, serial;

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

SEE ALSO

       ldattach(1), ioctl(2), ioctl_console(2), termios(3), pty(7)

COLOPHON

       This page is part of release 4.15 of the Linux man-pages project.  A description of the project, information about reporting bugs, and  the
       latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.

Linux                                                               2017-09-15                                                        IOCTL_TTY(2)