1IOCTL_TTY(2) Linux Programmer's Manual IOCTL_TTY(2)
2
6 ioctl_tty - ioctls for terminals and serial lines
7
9 #include <termios.h>
10 int ioctl(int fd, int cmd, ...);
12
14 The ioctl(2) call for terminals and serial ports accepts many possible
15 command arguments. Most require a third argument, of varying type,
16 here called argp or arg.
17 Use of ioctl makes for nonportable programs. Use the POSIX interface
19 described in termios(3) whenever possible.
20 Get and set terminal attributes
22 TCGETS struct termios *argp
23 Equivalent to tcgetattr(fd, argp).
24 Get the current serial port settings.
25 TCSETS const struct termios *argp
27 Equivalent to tcsetattr(fd, TCSANOW, argp).
28 Set the current serial port settings.
29 TCSETSW const struct termios *argp
31 Equivalent to tcsetattr(fd, TCSADRAIN, argp).
32 Allow the output buffer to drain, and set the current serial
33 port settings.
34 TCSETSF const struct termios *argp
36 Equivalent to tcsetattr(fd, TCSAFLUSH, argp).
37 Allow the output buffer to drain, discard pending input, and set
38 the current serial port settings.
39 The following four ioctls are just like TCGETS, TCSETS, TCSETSW,
41 TCSETSF, except that they take a struct termio * instead of a struct
42 termios *.
43 TCGETA struct termio *argp
45 TCSETA const struct termio *argp
47 TCSETAW const struct termio *argp
49 TCSETAF const struct termio *argp
51 Locking the termios structure
53 The termios structure of a terminal can be locked. The lock is itself
54 a termios structure, with nonzero bits or fields indicating a locked
55 value.
56 TIOCGLCKTRMIOS struct termios *argp
58 Gets the locking status of the termios structure of the termi‐
59 nal.
60 TIOCSLCKTRMIOS const struct termios *argp
62 Sets the locking status of the termios structure of the termi‐
63 nal. Only a process with the CAP_SYS_ADMIN capability can do
64 this.
65 Get and set window size
67 Window sizes are kept in the kernel, but not used by the kernel (except
68 in the case of virtual consoles, where the kernel will update the win‐
69 dow size when the size of the virtual console changes, for example, by
70 loading a new font).
71 The following constants and structure are defined in <sys/ioctl.h>.
73 TIOCGWINSZ struct winsize *argp
75 Get window size.
76 TIOCSWINSZ const struct winsize *argp
78 Set window size.
79 The struct used by these ioctls is defined as
81 struct winsize {
83 unsigned short ws_row;
84 unsigned short ws_col;
85 unsigned short ws_xpixel; /* unused */
86 unsigned short ws_ypixel; /* unused */
87 };
88 When the window size changes, a SIGWINCH signal is sent to the fore‐
90 ground process group.
91 Sending a break
93 TCSBRK int arg
94 Equivalent to tcsendbreak(fd, arg).
95 If the terminal is using asynchronous serial data transmission,
96 and arg is zero, then send a break (a stream of zero bits) for
97 between 0.25 and 0.5 seconds. If the terminal is not using
98 asynchronous serial data transmission, then either a break is
99 sent, or the function returns without doing anything. When arg
100 is nonzero, nobody knows what will happen.
101 (SVr4, UnixWare, Solaris, Linux treat tcsendbreak(fd,arg) with
103 nonzero arg like tcdrain(fd). SunOS treats arg as a multiplier,
104 and sends a stream of bits arg times as long as done for zero
105 arg. DG/UX and AIX treat arg (when nonzero) as a time interval
106 measured in milliseconds. HP-UX ignores arg.)
107 TCSBRKP int arg
109 So-called "POSIX version" of TCSBRK. It treats nonzero arg as a
110 timeinterval measured in deciseconds, and does nothing when the
111 driver does not support breaks.
112 TIOCSBRK void
114 Turn break on, that is, start sending zero bits.
115 TIOCCBRK void
117 Turn break off, that is, stop sending zero bits.
118 Software flow control
120 TCXONC int arg
121 Equivalent to tcflow(fd, arg).
122 See tcflow(3) for the argument values TCOOFF, TCOON, TCIOFF,
123 TCION.
124 Buffer count and flushing
126 FIONREAD int *argp
127 Get the number of bytes in the input buffer.
128 TIOCINQ int *argp
130 Same as FIONREAD.
131 TIOCOUTQ int *argp
133 Get the number of bytes in the output buffer.
134 TCFLSH int arg
136 Equivalent to tcflush(fd, arg).
137 See tcflush(3) for the argument values TCIFLUSH, TCOFLUSH,
138 TCIOFLUSH.
139 Faking input
141 TIOCSTI const char *argp
142 Insert the given byte in the input queue.
143 Redirecting console output
145 TIOCCONS void
146 Redirect output that would have gone to /dev/console or
147 /dev/tty0 to the given terminal. If that was a pseudoterminal
148 master, send it to the slave. In Linux before version 2.6.10,
149 anybody can do this as long as the output was not redirected
150 yet; since version 2.6.10, only a process with the CAP_SYS_ADMIN
151 capability may do this. If output was redirected already EBUSY
152 is returned, but redirection can be stopped by using this ioctl
153 with fd pointing at /dev/console or /dev/tty0.
154 Controlling terminal
156 TIOCSCTTY int arg
157 Make the given terminal the controlling terminal of the calling
158 process. The calling process must be a session leader and not
159 have a controlling terminal already. For this case, arg should
160 be specified as zero.
161 If this terminal is already the controlling terminal of a dif‐
163 ferent session group, then the ioctl fails with EPERM, unless
164 the caller has the CAP_SYS_ADMIN capability and arg equals 1, in
165 which case the terminal is stolen, and all processes that had it
166 as controlling terminal lose it.
167 TIOCNOTTY void
169 If the given terminal was the controlling terminal of the call‐
170 ing process, give up this controlling terminal. If the process
171 was session leader, then send SIGHUP and SIGCONT to the fore‐
172 ground process group and all processes in the current session
173 lose their controlling terminal.
174 Process group and session ID
176 TIOCGPGRP pid_t *argp
177 When successful, equivalent to *argp = tcgetpgrp(fd).
178 Get the process group ID of the foreground process group on this
179 terminal.
180 TIOCSPGRP const pid_t *argp
182 Equivalent to tcsetpgrp(fd, *argp).
183 Set the foreground process group ID of this terminal.
184 TIOCGSID pid_t *argp
186 Get the session ID of the given terminal. This fails with the
187 error ENOTTY if the terminal is not a master pseudoterminal and
188 not our controlling terminal. Strange.
189 Exclusive mode
191 TIOCEXCL void
192 Put the terminal into exclusive mode. No further open(2) opera‐
193 tions on the terminal are permitted. (They fail with EBUSY,
194 except for a process with the CAP_SYS_ADMIN capability.)
195 TIOCGEXCL int *argp
197 (since Linux 3.8) If the terminal is currently in exclusive
198 mode, place a nonzero value in the location pointed to by argp;
199 otherwise, place zero in *argp.
200 TIOCNXCL void
202 Disable exclusive mode.
203 Line discipline
205 TIOCGETD int *argp
206 Get the line discipline of the terminal.
207 TIOCSETD const int *argp
209 Set the line discipline of the terminal.
210 Pseudoterminal ioctls
212 TIOCPKT const int *argp
213 Enable (when *argp is nonzero) or disable packet mode. Can be
214 applied to the master side of a pseudoterminal only (and will
215 return ENOTTY otherwise). In packet mode, each subsequent
216 read(2) will return a packet that either contains a single
217 nonzero control byte, or has a single byte containing zero (' ')
218 followed by data written on the slave side of the pseudotermi‐
219 nal. If the first byte is not TIOCPKT_DATA (0), it is an OR of
220 one or more of the following bits:
221 TIOCPKT_FLUSHREAD The read queue for the terminal is flushed.
223 TIOCPKT_FLUSHWRITE The write queue for the terminal is flushed.
224 TIOCPKT_STOP Output to the terminal is stopped.
225 TIOCPKT_START Output to the terminal is restarted.
226 TIOCPKT_DOSTOP The start and stop characters are ^S/^Q.
227 TIOCPKT_NOSTOP The start and stop characters are not ^S/^Q.
228 While this mode is in use, the presence of control status infor‐
230 mation to be read from the master side may be detected by a
231 select(2) for exceptional conditions or a poll(2) for the POLL‐
232 PRI event.
233 This mode is used by rlogin(1) and rlogind(8) to implement a
235 remote-echoed, locally ^S/^Q flow-controlled remote login.
236 TIOCGPKT const int *argp
238 (since Linux 3.8) Return the current packet mode setting in the
239 integer pointed to by argp.
240 TIOCSPTLCK int *argp
242 Set (if *argp is nonzero) or remove (if *argp is zero) the pseu‐
243 doterminal slave device. (See also unlockpt(3).)
244 TIOCGPTLCK int *argp
246 (since Linux 3.8) Place the current lock state of the pseudoter‐
247 minal slave device in the location pointed to by argp.
248 TIOCGPTPEER int flags
250 (since Linux 4.13) Given a file descriptor in fd that refers to
251 a pseudoterminal master, open (with the given open(2)-style
252 flags) and return a new file descriptor that refers to the peer
253 pseudoterminal slave device. This operation can be performed
254 regardless of whether the pathname of the slave device is acces‐
255 sible through the calling process's mount namespace.
256 Security-conscious programs interacting with namespaces may wish
258 to use this operation rather than open(2) with the pathname
259 returned by ptsname(3), and similar library functions that have
260 insecure APIs. (For example, confusion can occur in some cases
261 using ptsname(3) with a pathname where a devpts filesystem has
262 been mounted in a different mount namespace.)
263 The BSD ioctls TIOCSTOP, TIOCSTART, TIOCUCNTL, TIOCREMOTE have not been
265 implemented under Linux.
266 Modem control
268 TIOCMGET int *argp
269 Get the status of modem bits.
270 TIOCMSET const int *argp
272 Set the status of modem bits.
273 TIOCMBIC const int *argp
275 Clear the indicated modem bits.
276 TIOCMBIS const int *argp
278 Set the indicated modem bits.
279 The following bits are used by the above ioctls:
281 TIOCM_LE DSR (data set ready/line enable)
283 TIOCM_DTR DTR (data terminal ready)
284 TIOCM_RTS RTS (request to send)
285 TIOCM_ST Secondary TXD (transmit)
286 TIOCM_SR Secondary RXD (receive)
287 TIOCM_CTS CTS (clear to send)
288 TIOCM_CAR DCD (data carrier detect)
289 TIOCM_CD see TIOCM_CAR
290 TIOCM_RNG RNG (ring)
291 TIOCM_RI see TIOCM_RNG
292 TIOCM_DSR DSR (data set ready)
293 TIOCMIWAIT int arg
295 Wait for any of the 4 modem bits (DCD, RI, DSR, CTS) to change.
296 The bits of interest are specified as a bit mask in arg, by
297 ORing together any of the bit values, TIOCM_RNG, TIOCM_DSR,
298 TIOCM_CD, and TIOCM_CTS. The caller should use TIOCGICOUNT to
299 see which bit has changed.
300 TIOCGICOUNT struct serial_icounter_struct *argp
302 Get counts of input serial line interrupts (DCD, RI, DSR, CTS).
303 The counts are written to the serial_icounter_struct structure
304 pointed to by argp.
305 Note: both 1->0 and 0->1 transitions are counted, except for RI,
307 where only 0->1 transitions are counted.
308 Marking a line as local
310 TIOCGSOFTCAR int *argp
311 ("Get software carrier flag") Get the status of the CLOCAL flag
312 in the c_cflag field of the termios structure.
313 TIOCSSOFTCAR const int *argp
315 ("Set software carrier flag") Set the CLOCAL flag in the termios
316 structure when *argp is nonzero, and clear it otherwise.
317 If the CLOCAL flag for a line is off, the hardware carrier detect (DCD)
319 signal is significant, and an open(2) of the corresponding terminal
320 will block until DCD is asserted, unless the O_NONBLOCK flag is given.
321 If CLOCAL is set, the line behaves as if DCD is always asserted. The
322 software carrier flag is usually turned on for local devices, and is
323 off for lines with modems.
324 Linux-specific
326 For the TIOCLINUX ioctl, see ioctl_console(2).
327 Kernel debugging
329 #include <linux/tty.h>
330 TIOCTTYGSTRUCT struct tty_struct *argp
332 Get the tty_struct corresponding to fd. This command was
333 removed in Linux 2.5.67.
334
336 The ioctl(2) system call returns 0 on success. On error, it returns -1
337 and sets errno appropriately.
338
340 EINVAL Invalid command parameter.
341 ENOIOCTLCMD
343 Unknown command.
344 ENOTTY Inappropriate fd.
346 EPERM Insufficient permission.
348
350 Check the condition of DTR on the serial port.
351 #include <termios.h>
353 #include <fcntl.h>
354 #include <sys/ioctl.h>
355 int
357 main(void)
358 {
359 int fd, serial;
360 fd = open("/dev/ttyS0", O_RDONLY);
362 ioctl(fd, TIOCMGET, &serial);
363 if (serial & TIOCM_DTR)
364 puts("TIOCM_DTR is set");
365 else
366 puts("TIOCM_DTR is not set");
367 close(fd);
368 }
369
371 ldattach(1), ioctl(2), ioctl_console(2), termios(3), pty(7)
372
374 This page is part of release 4.15 of the Linux man-pages project. A
375 description of the project, information about reporting bugs, and the
376 latest version of this page, can be found at
377 https://www.kernel.org/doc/man-pages/.
378Linux 2017-09-15 IOCTL_TTY(2)