1TTY_IOCTL(4) Linux Programmer's Manual TTY_IOCTL(4)
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6 tty_ioctl - ioctls for terminals and serial lines
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9 #include <termios.h>
10 int ioctl(int fd, int cmd, ...);
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14 The ioctl() 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 root (more precisely: a process with the
64 CAP_SYS_ADMIN capability) can do 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 pseudo-terminal
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 root (a process with the
151 CAP_SYS_ADMIN capability) may do this. If output was redirected
152 already EBUSY is returned, but redirection can be stopped by
153 using this ioctl 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. If this terminal is
160 already the controlling terminal of a different session group
161 then the ioctl fails with EPERM, unless the caller is root (more
162 precisely: has the CAP_SYS_ADMIN capability) and arg equals 1,
163 in which case the terminal is stolen, and all processes that had
164 it as controlling terminal lose it.
165 TIOCNOTTY void
167 If the given terminal was the controlling terminal of the call‐
168 ing process, give up this controlling terminal. If the process
169 was session leader, then send SIGHUP and SIGCONT to the fore‐
170 ground process group and all processes in the current session
171 lose their controlling terminal.
172 Process group and session ID
174 TIOCGPGRP pid_t *argp
175 When successful, equivalent to *argp = tcgetpgrp(fd).
176 Get the process group ID of the foreground process group on this
177 terminal.
178 TIOCSPGRP const pid_t *argp
180 Equivalent to tcsetpgrp(fd, *argp).
181 Set the foreground process group ID of this terminal.
182 TIOCGSID pid_t *argp
184 Get the session ID of the given terminal. This will fail with
185 ENOTTY in case the terminal is not a master pseudo-terminal and
186 not our controlling terminal. Strange.
187 Exclusive mode
189 TIOCEXCL void
190 Put the terminal into exclusive mode. No further open(2) opera‐
191 tions on the terminal are permitted. (They will fail with
192 EBUSY, except for root, that is, a process with the
193 CAP_SYS_ADMIN capability.)
194 TIOCNXCL void
196 Disable exclusive mode.
197 Line discipline
199 TIOCGETD int *argp
200 Get the line discipline of the terminal.
201 TIOCSETD const int *argp
203 Set the line discipline of the terminal.
204 Pseudo-terminal ioctls
206 TIOCPKT const int *argp
207 Enable (when *argp is nonzero) or disable packet mode. Can be
208 applied to the master side of a pseudo-terminal only (and will
209 return ENOTTY otherwise). In packet mode, each subsequent
210 read(2) will return a packet that either contains a single
211 nonzero control byte, or has a single byte containing zero (' ')
212 followed by data written on the slave side of the pseudo-termi‐
213 nal. If the first byte is not TIOCPKT_DATA (0), it is an OR of
214 one or more of the following bits:
215 TIOCPKT_FLUSHREAD The read queue for the terminal is flushed.
217 TIOCPKT_FLUSHWRITE The write queue for the terminal is flushed.
218 TIOCPKT_STOP Output to the terminal is stopped.
219 TIOCPKT_START Output to the terminal is restarted.
220 TIOCPKT_DOSTOP The start and stop characters are ^S/^Q.
221 TIOCPKT_NOSTOP The start and stop characters are not ^S/^Q.
222 While this mode is in use, the presence of control status infor‐
224 mation to be read from the master side may be detected by a
225 select(2) for exceptional conditions.
226 This mode is used by rlogin(1) and rlogind(8) to implement a
228 remote-echoed, locally ^S/^Q flow-controlled remote login.
229 The BSD ioctls TIOCSTOP, TIOCSTART, TIOCUCNTL, TIOCREMOTE have
231 not been implemented under Linux.
232 Modem control
234 TIOCMGET int *argp
235 get the status of modem bits.
236 TIOCMSET const int *argp
238 set the status of modem bits.
239 TIOCMBIC const int *argp
241 clear the indicated modem bits.
242 TIOCMBIS const int *argp
244 set the indicated modem bits.
245 Bits used by these four ioctls:
247 TIOCM_LE DSR (data set ready/line enable)
249 TIOCM_DTR DTR (data terminal ready)
250 TIOCM_RTS RTS (request to send)
251 TIOCM_ST Secondary TXD (transmit)
252 TIOCM_SR Secondary RXD (receive)
253 TIOCM_CTS CTS (clear to send)
254 TIOCM_CAR DCD (data carrier detect)
255 TIOCM_CD see TIOCM_CAR
256 TIOCM_RNG RNG (ring)
257 TIOCM_RI see TIOCM_RNG
258 TIOCM_DSR DSR (data set ready)
259 Marking a line as local
261 TIOCGSOFTCAR int *argp
262 ("Get software carrier flag") Get the status of the CLOCAL flag
263 in the c_cflag field of the termios structure.
264 TIOCSSOFTCAR const int *argp
266 ("Set software carrier flag") Set the CLOCAL flag in the termios
267 structure when *argp is nonzero, and clear it otherwise.
268 If the CLOCAL flag for a line is off, the hardware carrier detect (DCD)
270 signal is significant, and an open(2) of the corresponding terminal
271 will block until DCD is asserted, unless the O_NONBLOCK flag is given.
272 If CLOCAL is set, the line behaves as if DCD is always asserted. The
273 software carrier flag is usually turned on for local devices, and is
274 off for lines with modems.
275 Linux-specific
277 For the TIOCLINUX ioctl, see console_ioctl(4).
278 Kernel debugging
280 #include <linux/tty.h>
281 TIOCTTYGSTRUCT struct tty_struct *argp
283 Get the tty_struct corresponding to fd.
284
286 The ioctl() system call returns 0 on success. On error it returns -1
287 and sets errno appropriately.
288
290 EINVAL Invalid command parameter.
291 ENOIOCTLCMD
293 Unknown command.
294 ENOTTY Inappropriate fd.
296 EPERM Insufficient permission.
298
300 Check the condition of DTR on the serial port.
301 #include <termios.h>
303 #include <fcntl.h>
304 #include <sys/ioctl.h>
305 int
307 main(void)
308 {
309 int fd, serial;
310 fd = open("/dev/ttyS0", O_RDONLY);
312 ioctl(fd, TIOCMGET, &serial);
313 if (serial & TIOCM_DTR)
314 puts("TIOCM_DTR is not set");
315 else
316 puts("TIOCM_DTR is set");
317 close(fd);
318 }
319
321 ioctl(2), termios(3), console_ioctl(4), pty(7)
322
324 This page is part of release 3.25 of the Linux man-pages project. A
325 description of the project, and information about reporting bugs, can
326 be found at http://www.kernel.org/doc/man-pages/.
327Linux 2008-10-29 TTY_IOCTL(4)