.\" Copyright 2002 Walter Harms .\" and Andries Brouwer . .\" .\" %%%LICENSE_START(GPL_NOVERSION_ONELINE) .\" Distributed under GPL .\" %%%LICENSE_END .\" .TH IOCTL_TTY 2 2017-09-15 "Linux" "Linux Programmer's Manual" .SH NAME ioctl_tty \- ioctls for terminals and serial lines .SH SYNOPSIS .B "#include " .PP .BI "int ioctl(int " fd ", int " cmd ", ...);" .SH DESCRIPTION The .BR ioctl (2) call for terminals and serial ports accepts many possible command arguments. Most require a third argument, of varying type, here called .I argp or .IR arg . .PP Use of .I ioctl makes for nonportable programs. Use the POSIX interface described in .BR termios (3) whenever possible. .SS Get and set terminal attributes .TP .BI "TCGETS struct termios *" argp Equivalent to .IR "tcgetattr(fd, argp)" . .br Get the current serial port settings. .TP .BI "TCSETS const struct termios *" argp Equivalent to .IR "tcsetattr(fd, TCSANOW, argp)" . .br Set the current serial port settings. .TP .BI "TCSETSW const struct termios *" argp Equivalent to .IR "tcsetattr(fd, TCSADRAIN, argp)" . .br Allow the output buffer to drain, and set the current serial port settings. .TP .BI "TCSETSF const struct termios *" argp Equivalent to .IR "tcsetattr(fd, TCSAFLUSH, argp)" . .br Allow the output buffer to drain, discard pending input, and set the current serial port settings. .PP The following four ioctls are just like .BR TCGETS , .BR TCSETS , .BR TCSETSW , .BR TCSETSF , except that they take a .I "struct termio\ *" instead of a .IR "struct termios\ *" . .IP .BI "TCGETA struct termio *" argp .IP .BI "TCSETA const struct termio *" argp .IP .BI "TCSETAW const struct termio *" argp .IP .BI "TCSETAF const struct termio *" argp .SS Locking the termios structure The .I termios structure of a terminal can be locked. The lock is itself a .I termios structure, with nonzero bits or fields indicating a locked value. .TP .BI "TIOCGLCKTRMIOS struct termios *" argp Gets the locking status of the .I termios structure of the terminal. .TP .BI "TIOCSLCKTRMIOS const struct termios *" argp Sets the locking status of the .I termios structure of the terminal. Only a process with the .BR CAP_SYS_ADMIN capability can do this. .SS 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). .PP The following constants and structure are defined in .IR . .TP .BI "TIOCGWINSZ struct winsize *" argp Get window size. .TP .BI "TIOCSWINSZ const struct winsize *" argp Set window size. .PP The struct used by these ioctls is defined as .PP .in +4n .EX struct winsize { unsigned short ws_row; unsigned short ws_col; unsigned short ws_xpixel; /* unused */ unsigned short ws_ypixel; /* unused */ }; .EE .in .PP When the window size changes, a .B SIGWINCH signal is sent to the foreground process group. .SS Sending a break .TP .BI "TCSBRK int " arg Equivalent to .IR "tcsendbreak(fd, arg)" . .br If the terminal is using asynchronous serial data transmission, and .I 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 .I arg is nonzero, nobody knows what will happen. .IP (SVr4, UnixWare, Solaris, Linux treat .I "tcsendbreak(fd,arg)" with nonzero .I arg like .IR "tcdrain(fd)" . SunOS treats .I arg as a multiplier, and sends a stream of bits .I arg times as long as done for zero .IR arg . DG/UX and AIX treat .I arg (when nonzero) as a time interval measured in milliseconds. HP-UX ignores .IR arg .) .TP .BI "TCSBRKP int " arg So-called "POSIX version" of .BR TCSBRK . It treats nonzero .I arg as a timeinterval measured in deciseconds, and does nothing when the driver does not support breaks. .TP .B "TIOCSBRK void" Turn break on, that is, start sending zero bits. .TP .B "TIOCCBRK void" Turn break off, that is, stop sending zero bits. .SS Software flow control .TP .BI "TCXONC int " arg Equivalent to .IR "tcflow(fd, arg)" . .br See .BR tcflow (3) for the argument values .BR TCOOFF , .BR TCOON , .BR TCIOFF , .BR TCION . .SS Buffer count and flushing .TP .BI "FIONREAD int *" argp Get the number of bytes in the input buffer. .TP .BI "TIOCINQ int *" argp Same as .BR FIONREAD . .TP .BI "TIOCOUTQ int *" argp Get the number of bytes in the output buffer. .TP .BI "TCFLSH int " arg Equivalent to .IR "tcflush(fd, arg)" . .br See .BR tcflush (3) for the argument values .BR TCIFLUSH , .BR TCOFLUSH , .BR TCIOFLUSH . .SS Faking input .TP .BI "TIOCSTI const char *" argp Insert the given byte in the input queue. .SS Redirecting console output .TP .B "TIOCCONS void" Redirect output that would have gone to .I /dev/console or .I /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 .BR CAP_SYS_ADMIN capability may do this. If output was redirected already .B EBUSY is returned, but redirection can be stopped by using this ioctl with .I fd pointing at .I /dev/console or .IR /dev/tty0 . .SS Controlling terminal .TP .BI "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, .I arg should be specified as zero. .IP If this terminal is already the controlling terminal of a different session group, then the ioctl fails with .BR EPERM , unless the caller has the .BR CAP_SYS_ADMIN capability and .I arg equals 1, in which case the terminal is stolen, and all processes that had it as controlling terminal lose it. .TP .B "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 .B SIGHUP and .B SIGCONT to the foreground process group and all processes in the current session lose their controlling terminal. .SS Process group and session ID .TP .BI "TIOCGPGRP pid_t *" argp When successful, equivalent to .IR "*argp = tcgetpgrp(fd)" . .br Get the process group ID of the foreground process group on this terminal. .TP .BI "TIOCSPGRP const pid_t *" argp Equivalent to .IR "tcsetpgrp(fd, *argp)" . .br Set the foreground process group ID of this terminal. .TP .BI "TIOCGSID pid_t *" argp Get the session ID of the given terminal. This fails with the error .B ENOTTY if the terminal is not a master pseudoterminal and not our controlling terminal. Strange. .SS Exclusive mode .TP .B "TIOCEXCL void" Put the terminal into exclusive mode. No further .BR open (2) operations on the terminal are permitted. (They fail with .BR EBUSY , except for a process with the .BR CAP_SYS_ADMIN capability.) .TP .BI "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 .IR argp ; otherwise, place zero in .IR *argp . .TP .B "TIOCNXCL void" Disable exclusive mode. .SS Line discipline .TP .BI "TIOCGETD int *" argp Get the line discipline of the terminal. .TP .BI "TIOCSETD const int *" argp Set the line discipline of the terminal. .SS Pseudoterminal ioctls .TP .BI "TIOCPKT const int *" argp Enable (when .RI * argp is nonzero) or disable packet mode. Can be applied to the master side of a pseudoterminal only (and will return .B ENOTTY otherwise). In packet mode, each subsequent .BR read (2) will return a packet that either contains a single nonzero control byte, or has a single byte containing zero (\(aq\0\(aq) followed by data written on the slave side of the pseudoterminal. If the first byte is not .B TIOCPKT_DATA (0), it is an OR of one or more of the following bits: .IP .nf 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 \fB^S\fP/\fB^Q\fP. TIOCPKT_NOSTOP The start and stop characters are not \fB^S\fP/\fB^Q\fP. .fi .IP While this mode is in use, the presence of control status information to be read from the master side may be detected by a .BR select (2) for exceptional conditions or a .BR poll (2) for the .I POLLPRI event. .IP This mode is used by .BR rlogin (1) and .BR rlogind (8) to implement a remote-echoed, locally \fB^S\fP/\fB^Q\fP flow-controlled remote login. .TP .BI "TIOCGPKT const int *" argp (since Linux 3.8) Return the current packet mode setting in the integer pointed to by .IR argp . .TP .BI "TIOCSPTLCK int *" argp Set (if .IR *argp is nonzero) or remove (if .IR *argp is zero) the pseudoterminal slave device. (See also .BR unlockpt (3).) .TP .BI "TIOCGPTLCK int *" argp (since Linux 3.8) Place the current lock state of the pseudoterminal slave device in the location pointed to by .IR argp . .TP .BI "TIOCGPTPEER int " flags .\" commit 54ebbfb1603415d9953c150535850d30609ef077 (since Linux 4.13) Given a file descriptor in .I fd that refers to a pseudoterminal master, open (with the given .BR open (2)-style .IR 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. .IP Security-conscious programs interacting with namespaces may wish to use this operation rather than .BR open (2) with the pathname returned by .BR ptsname (3), and similar library functions that have insecure APIs. (For example, confusion can occur in some cases using .BR ptsname (3) with a pathname where a devpts filesystem has been mounted in a different mount namespace.) .PP The BSD ioctls .BR TIOCSTOP , .BR TIOCSTART , .BR TIOCUCNTL , .B TIOCREMOTE have not been implemented under Linux. .SS Modem control .TP .BI "TIOCMGET int *" argp Get the status of modem bits. .TP .BI "TIOCMSET const int *" argp Set the status of modem bits. .TP .BI "TIOCMBIC const int *" argp Clear the indicated modem bits. .TP .BI "TIOCMBIS const int *" argp Set the indicated modem bits. .PP The following bits are used by the above ioctls: .PP .nf 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) .fi .TP .BI "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 .IR arg , by ORing together any of the bit values, .BR TIOCM_RNG , .BR TIOCM_DSR , .BR TIOCM_CD , and .BR TIOCM_CTS . The caller should use .B TIOCGICOUNT to see which bit has changed. .TP .BI "TIOCGICOUNT struct serial_icounter_struct *" argp Get counts of input serial line interrupts (DCD, RI, DSR, CTS). The counts are written to the .I serial_icounter_struct structure pointed to by .IR argp . .IP Note: both 1->0 and 0->1 transitions are counted, except for RI, where only 0->1 transitions are counted. .SS Marking a line as local .TP .BI "TIOCGSOFTCAR int *" argp ("Get software carrier flag") Get the status of the CLOCAL flag in the c_cflag field of the .I termios structure. .TP .BI "TIOCSSOFTCAR const int *" argp ("Set software carrier flag") Set the CLOCAL flag in the .I termios structure when .RI * argp is nonzero, and clear it otherwise. .PP If the .B CLOCAL flag for a line is off, the hardware carrier detect (DCD) signal is significant, and an .BR open (2) of the corresponding terminal will block until DCD is asserted, unless the .B O_NONBLOCK flag is given. If .B 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. .SS Linux-specific For the .B TIOCLINUX ioctl, see .BR ioctl_console (2). .SS Kernel debugging .B "#include " .TP .BI "TIOCTTYGSTRUCT struct tty_struct *" argp Get the .I tty_struct corresponding to .IR fd . This command was removed in Linux 2.5.67. .\" commit b3506a09d15dc5aee6d4bb88d759b157016e1864 .\" Author: Andries E. Brouwer .\" Date: Tue Apr 1 04:42:46 2003 -0800 .\" .\" [PATCH] kill TIOCTTYGSTRUCT .\" .\" Only used for (dubious) debugging purposes, and exposes .\" internal kernel state. .\" .\" .SS Serial info .\" .BR "#include " .\" .PP .\" .TP .\" .BI "TIOCGSERIAL struct serial_struct *" argp .\" Get serial info. .\" .TP .\" .BI "TIOCSSERIAL const struct serial_struct *" argp .\" Set serial info. .SH RETURN VALUE The .BR ioctl (2) system call returns 0 on success. On error, it returns \-1 and sets .I errno appropriately. .SH ERRORS .TP .B EINVAL Invalid command parameter. .TP .B ENOIOCTLCMD Unknown command. .TP .B ENOTTY Inappropriate .IR fd . .TP .B EPERM Insufficient permission. .SH EXAMPLE Check the condition of DTR on the serial port. .PP .EX #include #include #include 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); } .EE .SH SEE ALSO .BR ldattach (1), .BR ioctl (2), .BR ioctl_console (2), .BR termios (3), .BR pty (7) .\" .\" FIONBIO const int * .\" FIONCLEX void .\" FIOCLEX void .\" FIOASYNC const int * .\" from serial.c: .\" TIOCSERCONFIG void .\" TIOCSERGWILD int * .\" TIOCSERSWILD const int * .\" TIOCSERGSTRUCT struct async_struct * .\" TIOCSERGETLSR int * .\" TIOCSERGETMULTI struct serial_multiport_struct * .\" TIOCSERSETMULTI const struct serial_multiport_struct * .\" TIOCGSERIAL, TIOCSSERIAL (see above) .SH COLOPHON This page is part of release 5.04 of the Linux .I 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/.