'\" t .\" Copyright 2002 Walter Harms .\" and Andries Brouwer . .\" .\" SPDX-License-Identifier: GPL-1.0-or-later .\" .TH ioctl_tty 2 2024-03-03 "Linux man-pages 6.7" .SH NAME ioctl_tty \- ioctls for terminals and serial lines .SH LIBRARY Standard C library .RI ( libc ", " \-lc ) .SH SYNOPSIS .nf .B #include .BR "#include " " /* Definition of " "struct termios" , .BR " struct termios2" ", and" .BR " Bnnn" ", " BOTHER ", " CBAUD ", " CLOCAL , .BR " TC*" { FLUSH , ON , OFF "} and other constants */" .P .BI "int ioctl(int " fd ", int " op ", ...);" .fi .SH DESCRIPTION The .BR ioctl (2) call for terminals and serial ports accepts many possible operation arguments. Most require a third argument, of varying type, here called .I argp or .IR arg . .P Use of .BR ioctl () makes for nonportable programs. Use the POSIX interface described in .BR termios (3) whenever possible. .P Please note that .B struct termios from .I is different and incompatible with .B struct termios from .IR . These ioctl calls require .B struct termios from .IR . .SS Get and set terminal attributes .TP .B TCGETS Argument: .BI "struct termios\~*" argp .IP Equivalent to .IR "tcgetattr(fd, argp)" . .IP Get the current serial port settings. .TP .B TCSETS Argument: .BI "const struct termios\~*" argp .IP Equivalent to .IR "tcsetattr(fd, TCSANOW, argp)" . .IP Set the current serial port settings. .TP .B TCSETSW Argument: .BI "const struct termios\~*" argp .IP Equivalent to .IR "tcsetattr(fd, TCSADRAIN, argp)" . .IP Allow the output buffer to drain, and set the current serial port settings. .TP .B TCSETSF Argument: .BI "const struct termios\~*" argp .IP Equivalent to .IR "tcsetattr(fd, TCSAFLUSH, argp)" . .IP Allow the output buffer to drain, discard pending input, and set the current serial port settings. .P The following four ioctls, added in Linux 2.6.20, .\" commit 64bb6c5e1ddcd47c951740485026ef08975ee2e6 .\" commit 592ee3a5e5e2a981ef2829a0380093006d045661 are just like .BR TCGETS , .BR TCSETS , .BR TCSETSW , .BR TCSETSF , except that they take a .I "struct termios2\~*" instead of a .IR "struct termios\~*" . If the structure member .B c_cflag contains the flag .BR BOTHER , then the baud rate is stored in the structure members .B c_ispeed and .B c_ospeed as integer values. These ioctls are not supported on all architectures. .RS .TS lb l. TCGETS2 \fBstruct termios2 *\fPargp TCSETS2 \fBconst struct termios2 *\fPargp TCSETSW2 \fBconst struct termios2 *\fPargp TCSETSF2 \fBconst struct termios2 *\fPargp .TE .RE .P 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\~*" . .RS .TS lb l. TCGETA \fBstruct termio *\fPargp TCSETA \fBconst struct termio *\fPargp TCSETAW \fBconst struct termio *\fPargp TCSETAF \fBconst struct termio *\fPargp .TE .RE .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 .B TIOCGLCKTRMIOS Argument: .BI "struct termios\~*" argp .IP Gets the locking status of the .I termios structure of the terminal. .TP .B TIOCSLCKTRMIOS Argument: .BI "const struct termios\~*" argp .IP Sets the locking status of the .I termios structure of the terminal. Only a process with the .B 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). .TP .B TIOCGWINSZ Argument: .BI "struct winsize\~*" argp .IP Get window size. .TP .B TIOCSWINSZ Argument: .BI "const struct winsize\~*" argp .IP Set window size. .P The struct used by these ioctls is defined as .P .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 .P When the window size changes, a .B SIGWINCH signal is sent to the foreground process group. .SS Sending a break .TP .B TCSBRK Argument: .BI "int " arg .IP Equivalent to .IR "tcsendbreak(fd, arg)" . .IP 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, and 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 .B TCSBRKP Argument: .BI "int " arg .IP So-called "POSIX version" of .BR TCSBRK . It treats nonzero .I arg as a time interval measured in deciseconds, and does nothing when the driver does not support breaks. .TP .B TIOCSBRK Argument: .B void .IP Turn break on, that is, start sending zero bits. .TP .B TIOCCBRK Argument: .B void .IP Turn break off, that is, stop sending zero bits. .SS Software flow control .TP .B TCXONC Argument: .BI "int " arg .IP Equivalent to .IR "tcflow(fd, arg)" . .IP See .BR tcflow (3) for the argument values .BR TCOOFF , .BR TCOON , .BR TCIOFF , .BR TCION . .SS Buffer count and flushing .TP .B FIONREAD Argument: .BI "int\~*" argp .IP Get the number of bytes in the input buffer. .TP .B TIOCINQ Argument: .BI "int\~*" argp .IP Same as .BR FIONREAD . .TP .B TIOCOUTQ Argument: .BI "int\~*" argp .IP Get the number of bytes in the output buffer. .TP .B TCFLSH Argument: .BI "int " arg .IP Equivalent to .IR "tcflush(fd, arg)" . .IP See .BR tcflush (3) for the argument values .BR TCIFLUSH , .BR TCOFLUSH , .BR TCIOFLUSH . .TP .B TIOCSERGETLSR Argument: .BI "int\~*" argp .IP Get line status register. Status register has .B TIOCSER_TEMT bit set when output buffer is empty and also hardware transmitter is physically empty. .IP Does not have to be supported by all serial tty drivers. .IP .BR tcdrain (3) does not wait and returns immediately when .B TIOCSER_TEMT bit is set. .SS Faking input .TP .B TIOCSTI Argument: .BI "const char\~*" argp .IP Insert the given byte in the input queue. .IP Since Linux 6.2, .\" commit 690c8b804ad2eafbd35da5d3c95ad325ca7d5061 .\" commit 83efeeeb3d04b22aaed1df99bc70a48fe9d22c4d this operation may require the .B CAP_SYS_ADMIN capability (if the .I dev.tty.legacy_tiocsti sysctl variable is set to false). .SS Redirecting console output .TP .B TIOCCONS Argument: .B void .IP 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. Before Linux 2.6.10, anybody can do this as long as the output was not redirected yet; since Linux 2.6.10, only a process with the .B CAP_SYS_ADMIN capability may do this. If output was redirected already, then .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 .B TIOCSCTTY Argument: .BI "int " arg .IP 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 .B 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 Argument: .B void .IP 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 .B TIOCGPGRP Argument: .BI "pid_t\~*" argp .IP When successful, equivalent to .IR "*argp = tcgetpgrp(fd)" . .IP Get the process group ID of the foreground process group on this terminal. .TP .B TIOCSPGRP Argument: .BI "const pid_t\~*" argp .IP Equivalent to .IR "tcsetpgrp(fd, *argp)" . .IP Set the foreground process group ID of this terminal. .TP .B TIOCGSID Argument: .BI "pid_t\~*" argp .IP When successful, equivalent to .IR "*argp = tcgetsid(fd)" . .IP 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 Argument: .B void .IP 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 .B CAP_SYS_ADMIN capability.) .TP .B TIOCGEXCL Argument: .BI "int\~*" argp .IP (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 Argument: .B void .IP Disable exclusive mode. .SS Line discipline .TP .B TIOCGETD Argument: .BI "int\~*" argp .IP Get the line discipline of the terminal. .TP .B TIOCSETD Argument: .BI "const int\~*" argp .IP Set the line discipline of the terminal. .SS Pseudoterminal ioctls .TP .B TIOCPKT Argument: .BI "const int\~*" argp .IP 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]\e0\[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 .ad l .TS lb l. TIOCPKT_FLUSHREAD T{ The read queue for the terminal is flushed. T} TIOCPKT_FLUSHWRITE T{ The write queue for the terminal is flushed. T} TIOCPKT_STOP T{ Output to the terminal is stopped. T} TIOCPKT_START T{ Output to the terminal is restarted. T} TIOCPKT_DOSTOP T{ The start and stop characters are \fB\[ha]S\fP/\fB\[ha]Q\fP. T} TIOCPKT_NOSTOP T{ The start and stop characters are not \fB\[ha]S\fP/\fB\[ha]Q\fP. T} .TE .ad .IP While packet 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 .B POLLPRI event. .IP This mode is used by .BR rlogin (1) and .BR rlogind (8) to implement a remote-echoed, locally \fB\[ha]S\fP/\fB\[ha]Q\fP flow-controlled remote login. .TP .B TIOCGPKT Argument: .BI "const int\~*" argp .IP (since Linux 3.8) Return the current packet mode setting in the integer pointed to by .IR argp . .TP .B TIOCSPTLCK Argument: .BI "int\~*" argp .IP Set (if .I *argp is nonzero) or remove (if .I *argp is zero) the lock on the pseudoterminal slave device. (See also .BR unlockpt (3).) .TP .B TIOCGPTLCK Argument: .BI "int\~*" argp .IP (since Linux 3.8) Place the current lock state of the pseudoterminal slave device in the location pointed to by .IR argp . .TP .B TIOCGPTPEER Argument: .BI "int " flags .IP .\" 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.) .P The BSD ioctls .BR TIOCSTOP , .BR TIOCSTART , .BR TIOCUCNTL , and .B TIOCREMOTE have not been implemented under Linux. .SS Modem control .TP .B TIOCMGET Argument: .BI "int\~*" argp .IP Get the status of modem bits. .TP .B TIOCMSET Argument: .BI "const int\~*" argp .IP Set the status of modem bits. .TP .B TIOCMBIC Argument: .BI "const int\~*" argp .IP Clear the indicated modem bits. .TP .B TIOCMBIS Argument: .BI "const int\~*" argp .IP Set the indicated modem bits. .P The following bits are used by the above ioctls: .P .TS lb l. 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) .TE .TP .B TIOCMIWAIT Argument: .BI "int " arg .IP 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 .B TIOCGICOUNT Argument: .BI "struct serial_icounter_struct\~*" argp .IP 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 .B TIOCGSOFTCAR Argument: .BI "int\~*" argp .IP ("Get software carrier flag") Get the status of the CLOCAL flag in the c_cflag field of the .I termios structure. .TP .B TIOCSSOFTCAR Argument: .BI "const int\~*" argp .IP ("Set software carrier flag") Set the CLOCAL flag in the .I termios structure when .RI * argp is nonzero, and clear it otherwise. .P 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 .B TIOCTTYGSTRUCT Argument: .BI "struct tty_struct\~*" argp .IP Get the .I tty_struct corresponding to .IR fd . This operation 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 " .\" .P .\" .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 to indicate the error. .SH ERRORS .TP .B EINVAL Invalid operation parameter. .TP .B ENOIOCTLCMD Unknown operation. .TP .B ENOTTY Inappropriate .IR fd . .TP .B EPERM Insufficient permission. .SH EXAMPLES Check the condition of DTR on the serial port. .P .\" SRC BEGIN (tiocmget.c) .EX #include #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 .\" SRC END .P Get or set arbitrary baudrate on the serial port. .P .\" SRC BEGIN (tcgets.c) .EX /* SPDX-License-Identifier: GPL-2.0-or-later */ \& #include #include #include #include #include #include \& int main(int argc, char *argv[]) { #if !defined BOTHER fprintf(stderr, "BOTHER is unsupported\en"); /* Program may fallback to TCGETS/TCSETS with Bnnn constants */ exit(EXIT_FAILURE); #else /* Declare tio structure, its type depends on supported ioctl */ # if defined TCGETS2 struct termios2 tio; # else struct termios tio; # endif int fd, rc; \& if (argc != 2 && argc != 3 && argc != 4) { fprintf(stderr, "Usage: %s device [output [input] ]\en", argv[0]); exit(EXIT_FAILURE); } \& fd = open(argv[1], O_RDWR | O_NONBLOCK | O_NOCTTY); if (fd < 0) { perror("open"); exit(EXIT_FAILURE); } \& /* Get the current serial port settings via supported ioctl */ # if defined TCGETS2 rc = ioctl(fd, TCGETS2, &tio); # else rc = ioctl(fd, TCGETS, &tio); # endif if (rc) { perror("TCGETS"); close(fd); exit(EXIT_FAILURE); } \& /* Change baud rate when more arguments were provided */ if (argc == 3 || argc == 4) { /* Clear the current output baud rate and fill a new value */ tio.c_cflag &= \[ti]CBAUD; tio.c_cflag |= BOTHER; tio.c_ospeed = atoi(argv[2]); \& /* Clear the current input baud rate and fill a new value */ tio.c_cflag &= \[ti](CBAUD << IBSHIFT); tio.c_cflag |= BOTHER << IBSHIFT; /* When 4th argument is not provided reuse output baud rate */ tio.c_ispeed = (argc == 4) ? atoi(argv[3]) : atoi(argv[2]); \& /* Set new serial port settings via supported ioctl */ # if defined TCSETS2 rc = ioctl(fd, TCSETS2, &tio); # else rc = ioctl(fd, TCSETS, &tio); # endif if (rc) { perror("TCSETS"); close(fd); exit(EXIT_FAILURE); } \& /* And get new values which were really configured */ # if defined TCGETS2 rc = ioctl(fd, TCGETS2, &tio); # else rc = ioctl(fd, TCGETS, &tio); # endif if (rc) { perror("TCGETS"); close(fd); exit(EXIT_FAILURE); } } \& close(fd); \& printf("output baud rate: %u\en", tio.c_ospeed); printf("input baud rate: %u\en", tio.c_ispeed); \& exit(EXIT_SUCCESS); #endif } .EE .\" SRC END .SH SEE ALSO .BR ldattach (8), .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 * .\" TIOCSERGETMULTI struct serial_multiport_struct * .\" TIOCSERSETMULTI const struct serial_multiport_struct * .\" TIOCGSERIAL, TIOCSSERIAL (see above)