1ioctl_tty(2) System Calls Manual ioctl_tty(2)
2
6 ioctl_tty - ioctls for terminals and serial lines
7
9 Standard C library (libc, -lc)
10
12 #include <sys/ioctl.h>
13 #include <asm/termbits.h> /* Definition of struct termios,
14 struct termios2, and
15 Bnnn, BOTHER, CBAUD, CLOCAL,
16 TC*{FLUSH,ON,OFF} and other constants */
17 int ioctl(int fd, int cmd, ...);
19
21 The ioctl(2) call for terminals and serial ports accepts many possible
22 command arguments. Most require a third argument, of varying type,
23 here called argp or arg.
24 Use of ioctl() makes for nonportable programs. Use the POSIX interface
26 described in termios(3) whenever possible.
27 Please note that struct termios from <asm/termbits.h> is different and
29 incompatible with struct termios from <termios.h>. These ioctl calls
30 require struct termios from <asm/termbits.h>.
31 Get and set terminal attributes
33 TCGETS Argument: struct termios *argp
34 Equivalent to tcgetattr(fd, argp).
36 Get the current serial port settings.
38 TCSETS Argument: const struct termios *argp
40 Equivalent to tcsetattr(fd, TCSANOW, argp).
42 Set the current serial port settings.
44 TCSETSW
46 Argument: const struct termios *argp
47 Equivalent to tcsetattr(fd, TCSADRAIN, argp).
49 Allow the output buffer to drain, and set the current serial
51 port settings.
52 TCSETSF
54 Argument: const struct termios *argp
55 Equivalent to tcsetattr(fd, TCSAFLUSH, argp).
57 Allow the output buffer to drain, discard pending input, and set
59 the current serial port settings.
60 The following four ioctls, added in Linux 2.6.20, are just like TCGETS,
62 TCSETS, TCSETSW, TCSETSF, except that they take a struct termios2 * in‐
63 stead of a struct termios *. If the structure member c_cflag contains
64 the flag BOTHER, then the baud rate is stored in the structure members
65 c_ispeed and c_ospeed as integer values. These ioctls are not sup‐
66 ported on all architectures.
67 TCGETS2 struct termios2 *argp
69 TCSETS2 const struct termios2 *argp
70 TCSETSW2 const struct termios2 *argp
71 TCSETSF2 const struct termios2 *argp
72 The following four ioctls are just like TCGETS, TCSETS, TCSETSW, TC‐
74 SETSF, except that they take a struct termio * instead of a struct
75 termios *.
76 TCGETA struct termio *argp
78 TCSETA const struct termio *argp
79 TCSETAW const struct termio *argp
80 TCSETAF const struct termio *argp
81 Locking the termios structure
83 The termios structure of a terminal can be locked. The lock is itself
84 a termios structure, with nonzero bits or fields indicating a locked
85 value.
86 TIOCGLCKTRMIOS
88 Argument: struct termios *argp
89 Gets the locking status of the termios structure of the termi‐
91 nal.
92 TIOCSLCKTRMIOS
94 Argument: const struct termios *argp
95 Sets the locking status of the termios structure of the termi‐
97 nal. Only a process with the CAP_SYS_ADMIN capability can do
98 this.
99 Get and set window size
101 Window sizes are kept in the kernel, but not used by the kernel (except
102 in the case of virtual consoles, where the kernel will update the win‐
103 dow size when the size of the virtual console changes, for example, by
104 loading a new font).
105 TIOCGWINSZ
107 Argument: struct winsize *argp
108 Get window size.
110 TIOCSWINSZ
112 Argument: const struct winsize *argp
113 Set window size.
115 The struct used by these ioctls is defined as
117 struct winsize {
119 unsigned short ws_row;
120 unsigned short ws_col;
121 unsigned short ws_xpixel; /* unused */
122 unsigned short ws_ypixel; /* unused */
123 };
124 When the window size changes, a SIGWINCH signal is sent to the fore‐
126 ground process group.
127 Sending a break
129 TCSBRK Argument: int arg
130 Equivalent to tcsendbreak(fd, arg).
132 If the terminal is using asynchronous serial data transmission,
134 and arg is zero, then send a break (a stream of zero bits) for
135 between 0.25 and 0.5 seconds. If the terminal is not using
136 asynchronous serial data transmission, then either a break is
137 sent, or the function returns without doing anything. When arg
138 is nonzero, nobody knows what will happen.
139 (SVr4, UnixWare, Solaris, and Linux treat tcsendbreak(fd,arg)
141 with nonzero arg like tcdrain(fd). SunOS treats arg as a multi‐
142 plier, and sends a stream of bits arg times as long as done for
143 zero arg. DG/UX and AIX treat arg (when nonzero) as a time in‐
144 terval measured in milliseconds. HP-UX ignores arg.)
145 TCSBRKP
147 Argument: int arg
148 So-called "POSIX version" of TCSBRK. It treats nonzero arg as a
150 time interval measured in deciseconds, and does nothing when the
151 driver does not support breaks.
152 TIOCSBRK
154 Argument: void
155 Turn break on, that is, start sending zero bits.
157 TIOCCBRK
159 Argument: void
160 Turn break off, that is, stop sending zero bits.
162 Software flow control
164 TCXONC Argument: int arg
165 Equivalent to tcflow(fd, arg).
167 See tcflow(3) for the argument values TCOOFF, TCOON, TCIOFF,
169 TCION.
170 Buffer count and flushing
172 FIONREAD
173 Argument: int *argp
174 Get the number of bytes in the input buffer.
176 TIOCINQ
178 Argument: int *argp
179 Same as FIONREAD.
181 TIOCOUTQ
183 Argument: int *argp
184 Get the number of bytes in the output buffer.
186 TCFLSH Argument: int arg
188 Equivalent to tcflush(fd, arg).
190 See tcflush(3) for the argument values TCIFLUSH, TCOFLUSH,
192 TCIOFLUSH.
193 TIOCSERGETLSR
195 Argument: int *argp
196 Get line status register. Status register has TIOCSER_TEMT bit
198 set when output buffer is empty and also hardware transmitter is
199 physically empty.
200 Does not have to be supported by all serial tty drivers.
202 tcdrain(3) does not wait and returns immediately when TI‐
204 OCSER_TEMT bit is set.
205 Faking input
207 TIOCSTI
208 Argument: const char *argp
209 Insert the given byte in the input queue.
211 Redirecting console output
213 TIOCCONS
214 Argument: void
215 Redirect output that would have gone to /dev/console or
217 /dev/tty0 to the given terminal. If that was a pseudoterminal
218 master, send it to the slave. Before Linux 2.6.10, anybody can
219 do this as long as the output was not redirected yet; since
220 Linux 2.6.10, only a process with the CAP_SYS_ADMIN capability
221 may do this. If output was redirected already, then EBUSY is
222 returned, but redirection can be stopped by using this ioctl
223 with fd pointing at /dev/console or /dev/tty0.
224 Controlling terminal
226 TIOCSCTTY
227 Argument: int arg
228 Make the given terminal the controlling terminal of the calling
230 process. The calling process must be a session leader and not
231 have a controlling terminal already. For this case, arg should
232 be specified as zero.
233 If this terminal is already the controlling terminal of a dif‐
235 ferent session group, then the ioctl fails with EPERM, unless
236 the caller has the CAP_SYS_ADMIN capability and arg equals 1, in
237 which case the terminal is stolen, and all processes that had it
238 as controlling terminal lose it.
239 TIOCNOTTY
241 Argument: void
242 If the given terminal was the controlling terminal of the call‐
244 ing process, give up this controlling terminal. If the process
245 was session leader, then send SIGHUP and SIGCONT to the fore‐
246 ground process group and all processes in the current session
247 lose their controlling terminal.
248 Process group and session ID
250 TIOCGPGRP
251 Argument: pid_t *argp
252 When successful, equivalent to *argp = tcgetpgrp(fd).
254 Get the process group ID of the foreground process group on this
256 terminal.
257 TIOCSPGRP
259 Argument: const pid_t *argp
260 Equivalent to tcsetpgrp(fd, *argp).
262 Set the foreground process group ID of this terminal.
264 TIOCGSID
266 Argument: pid_t *argp
267 When successful, equivalent to *argp = tcgetsid(fd).
269 Get the session ID of the given terminal. This fails with the
271 error ENOTTY if the terminal is not a master pseudoterminal and
272 not our controlling terminal. Strange.
273 Exclusive mode
275 TIOCEXCL
276 Argument: void
277 Put the terminal into exclusive mode. No further open(2) opera‐
279 tions on the terminal are permitted. (They fail with EBUSY, ex‐
280 cept for a process with the CAP_SYS_ADMIN capability.)
281 TIOCGEXCL
283 Argument: int *argp
284 (since Linux 3.8) If the terminal is currently in exclusive
286 mode, place a nonzero value in the location pointed to by argp;
287 otherwise, place zero in *argp.
288 TIOCNXCL
290 Argument: void
291 Disable exclusive mode.
293 Line discipline
295 TIOCGETD
296 Argument: int *argp
297 Get the line discipline of the terminal.
299 TIOCSETD
301 Argument: const int *argp
302 Set the line discipline of the terminal.
304 Pseudoterminal ioctls
306 TIOCPKT
307 Argument: const int *argp
308 Enable (when *argp is nonzero) or disable packet mode. Can be
310 applied to the master side of a pseudoterminal only (and will
311 return ENOTTY otherwise). In packet mode, each subsequent
312 read(2) will return a packet that either contains a single non‐
313 zero control byte, or has a single byte containing zero ('\0')
314 followed by data written on the slave side of the pseudotermi‐
315 nal. If the first byte is not TIOCPKT_DATA (0), it is an OR of
316 one or more of the following bits:
317 TIOCPKT_FLUSHREAD The read queue for the
319 terminal is flushed.
320 TIOCPKT_FLUSHWRITE The write queue for the
321 terminal is flushed.
322 TIOCPKT_STOP Output to the terminal is
323 stopped.
324 TIOCPKT_START Output to the terminal is
325 restarted.
326 TIOCPKT_DOSTOP The start and stop charac‐
327 ters are ^S/^Q.
328 TIOCPKT_NOSTOP The start and stop charac‐
329 ters are not ^S/^Q.
330 While packet mode is in use, the presence of control status in‐
332 formation to be read from the master side may be detected by a
333 select(2) for exceptional conditions or a poll(2) for the POLL‐
334 PRI event.
335 This mode is used by rlogin(1) and rlogind(8) to implement a re‐
337 mote-echoed, locally ^S/^Q flow-controlled remote login.
338 TIOCGPKT
340 Argument: const int *argp
341 (since Linux 3.8) Return the current packet mode setting in the
343 integer pointed to by argp.
344 TIOCSPTLCK
346 Argument: int *argp
347 Set (if *argp is nonzero) or remove (if *argp is zero) the lock
349 on the pseudoterminal slave device. (See also unlockpt(3).)
350 TIOCGPTLCK
352 Argument: int *argp
353 (since Linux 3.8) Place the current lock state of the pseudoter‐
355 minal slave device in the location pointed to by argp.
356 TIOCGPTPEER
358 Argument: int flags
359 (since Linux 4.13) Given a file descriptor in fd that refers to
361 a pseudoterminal master, open (with the given open(2)-style
362 flags) and return a new file descriptor that refers to the peer
363 pseudoterminal slave device. This operation can be performed
364 regardless of whether the pathname of the slave device is acces‐
365 sible through the calling process's mount namespace.
366 Security-conscious programs interacting with namespaces may wish
368 to use this operation rather than open(2) with the pathname re‐
369 turned by ptsname(3), and similar library functions that have
370 insecure APIs. (For example, confusion can occur in some cases
371 using ptsname(3) with a pathname where a devpts filesystem has
372 been mounted in a different mount namespace.)
373 The BSD ioctls TIOCSTOP, TIOCSTART, TIOCUCNTL, and TIOCREMOTE have not
375 been implemented under Linux.
376 Modem control
378 TIOCMGET
379 Argument: int *argp
380 Get the status of modem bits.
382 TIOCMSET
384 Argument: const int *argp
385 Set the status of modem bits.
387 TIOCMBIC
389 Argument: const int *argp
390 Clear the indicated modem bits.
392 TIOCMBIS
394 Argument: const int *argp
395 Set the indicated modem bits.
397 The following bits are used by the above ioctls:
399 TIOCM_LE DSR (data set ready/line enable)
401 TIOCM_DTR DTR (data terminal ready)
402 TIOCM_RTS RTS (request to send)
403 TIOCM_ST Secondary TXD (transmit)
404 TIOCM_SR Secondary RXD (receive)
405 TIOCM_CTS CTS (clear to send)
406 TIOCM_CAR DCD (data carrier detect)
407 TIOCM_CD see TIOCM_CAR
408 TIOCM_RNG RNG (ring)
409 TIOCM_RI see TIOCM_RNG
410 TIOCM_DSR DSR (data set ready)
411 TIOCMIWAIT
413 Argument: int arg
414 Wait for any of the 4 modem bits (DCD, RI, DSR, CTS) to change.
416 The bits of interest are specified as a bit mask in arg, by OR‐
417 ing together any of the bit values, TIOCM_RNG, TIOCM_DSR, TI‐
418 OCM_CD, and TIOCM_CTS. The caller should use TIOCGICOUNT to see
419 which bit has changed.
420 TIOCGICOUNT
422 Argument: struct serial_icounter_struct *argp
423 Get counts of input serial line interrupts (DCD, RI, DSR, CTS).
425 The counts are written to the serial_icounter_struct structure
426 pointed to by argp.
427 Note: both 1->0 and 0->1 transitions are counted, except for RI,
429 where only 0->1 transitions are counted.
430 Marking a line as local
432 TIOCGSOFTCAR
433 Argument: int *argp
434 ("Get software carrier flag") Get the status of the CLOCAL flag
436 in the c_cflag field of the termios structure.
437 TIOCSSOFTCAR
439 Argument: const int *argp
440 ("Set software carrier flag") Set the CLOCAL flag in the termios
442 structure when *argp is nonzero, and clear it otherwise.
443 If the CLOCAL flag for a line is off, the hardware carrier detect (DCD)
445 signal is significant, and an open(2) of the corresponding terminal
446 will block until DCD is asserted, unless the O_NONBLOCK flag is given.
447 If CLOCAL is set, the line behaves as if DCD is always asserted. The
448 software carrier flag is usually turned on for local devices, and is
449 off for lines with modems.
450 Linux-specific
452 For the TIOCLINUX ioctl, see ioctl_console(2).
453 Kernel debugging
455 #include <linux/tty.h>
456 TIOCTTYGSTRUCT
458 Argument: struct tty_struct *argp
459 Get the tty_struct corresponding to fd. This command was re‐
461 moved in Linux 2.5.67.
462
464 The ioctl(2) system call returns 0 on success. On error, it returns -1
465 and sets errno to indicate the error.
466
468 EINVAL Invalid command parameter.
469 ENOIOCTLCMD
471 Unknown command.
472 ENOTTY Inappropriate fd.
474 EPERM Insufficient permission.
476
478 Check the condition of DTR on the serial port.
479 #include <fcntl.h>
481 #include <stdio.h>
482 #include <sys/ioctl.h>
483 #include <unistd.h>
484 int
486 main(void)
487 {
488 int fd, serial;
489 fd = open("/dev/ttyS0", O_RDONLY);
491 ioctl(fd, TIOCMGET, &serial);
492 if (serial & TIOCM_DTR)
493 puts("TIOCM_DTR is set");
494 else
495 puts("TIOCM_DTR is not set");
496 close(fd);
497 }
498 Get or set arbitrary baudrate on the serial port.
500 /* SPDX-License-Identifier: GPL-2.0-or-later */
502 #include <asm/termbits.h>
504 #include <fcntl.h>
505 #include <stdio.h>
506 #include <stdlib.h>
507 #include <sys/ioctl.h>
508 #include <unistd.h>
509 int
511 main(int argc, char *argv[])
512 {
513 #if !defined BOTHER
514 fprintf(stderr, "BOTHER is unsupported\n");
515 /* Program may fallback to TCGETS/TCSETS with Bnnn constants */
516 exit(EXIT_FAILURE);
517 #else
518 /* Declare tio structure, its type depends on supported ioctl */
519 # if defined TCGETS2
520 struct termios2 tio;
521 # else
522 struct termios tio;
523 # endif
524 int fd, rc;
525 if (argc != 2 && argc != 3 && argc != 4) {
527 fprintf(stderr, "Usage: %s device [output [input] ]\n", argv[0]);
528 exit(EXIT_FAILURE);
529 }
530 fd = open(argv[1], O_RDWR | O_NONBLOCK | O_NOCTTY);
532 if (fd < 0) {
533 perror("open");
534 exit(EXIT_FAILURE);
535 }
536 /* Get the current serial port settings via supported ioctl */
538 # if defined TCGETS2
539 rc = ioctl(fd, TCGETS2, &tio);
540 # else
541 rc = ioctl(fd, TCGETS, &tio);
542 # endif
543 if (rc) {
544 perror("TCGETS");
545 close(fd);
546 exit(EXIT_FAILURE);
547 }
548 /* Change baud rate when more arguments were provided */
550 if (argc == 3 || argc == 4) {
551 /* Clear the current output baud rate and fill a new value */
552 tio.c_cflag &= ~CBAUD;
553 tio.c_cflag |= BOTHER;
554 tio.c_ospeed = atoi(argv[2]);
555 /* Clear the current input baud rate and fill a new value */
557 tio.c_cflag &= ~(CBAUD << IBSHIFT);
558 tio.c_cflag |= BOTHER << IBSHIFT;
559 /* When 4th argument is not provided reuse output baud rate */
560 tio.c_ispeed = (argc == 4) ? atoi(argv[3]) : atoi(argv[2]);
561 /* Set new serial port settings via supported ioctl */
563 # if defined TCSETS2
564 rc = ioctl(fd, TCSETS2, &tio);
565 # else
566 rc = ioctl(fd, TCSETS, &tio);
567 # endif
568 if (rc) {
569 perror("TCSETS");
570 close(fd);
571 exit(EXIT_FAILURE);
572 }
573 /* And get new values which were really configured */
575 # if defined TCGETS2
576 rc = ioctl(fd, TCGETS2, &tio);
577 # else
578 rc = ioctl(fd, TCGETS, &tio);
579 # endif
580 if (rc) {
581 perror("TCGETS");
582 close(fd);
583 exit(EXIT_FAILURE);
584 }
585 }
586 close(fd);
588 printf("output baud rate: %u\n", tio.c_ospeed);
590 printf("input baud rate: %u\n", tio.c_ispeed);
591 exit(EXIT_SUCCESS);
593 #endif
594 }
595
597 ldattach(8), ioctl(2), ioctl_console(2), termios(3), pty(7)
598Linux man-pages 6.04 2023-02-05 ioctl_tty(2)