1.\" Copyright (c) 1991, 1992, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 3. All advertising materials mentioning features or use of this software 13.\" must display the following acknowledgement: 14.\" This product includes software developed by the University of 15.\" California, Berkeley and its contributors. 16.\" 4. Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" @(#)tty.4 8.3 (Berkeley) 4/19/94 33.\" $FreeBSD$ 34.\" 35.Dd August 14, 1992 36.Dt TTY 4 37.Os 38.Sh NAME 39.Nm tty 40.Nd general terminal interface 41.Sh SYNOPSIS 42.In sys/ioctl.h 43.Sh DESCRIPTION 44This section describes the interface to the terminal drivers 45in the system. 46.Ss Terminal Special Files 47Each hardware terminal port on the system usually has a terminal special device 48file associated with it in the directory ``/dev/'' (for 49example, ``/dev/tty03''). 50When a user logs into 51the system on one of these hardware terminal ports, the system has already 52opened the associated device and prepared the line for normal interactive 53use (see 54.Xr getty 8 . ) 55There is also a special case of a terminal file that connects not to 56a hardware terminal port, but to another program on the other side. 57These special terminal devices are called 58.Em ptys 59and provide the mechanism necessary to give users the same interface to the 60system when logging in over a network (using 61.Xr rlogin 1 , 62or 63.Xr telnet 1 64for example). 65Even in these cases the details of how the terminal 66file was opened and set up is already handled by special software 67in the system. 68Thus, users do not normally need to worry about the details of 69how these lines are opened or used. 70Also, these lines are often used 71for dialing out of a system (through an out-calling modem), but again 72the system provides programs that hide the details of accessing 73these terminal special files (see 74.Xr tip 1 ) . 75.Pp 76When an interactive user logs in, the system prepares the line to 77behave in a certain way (called a 78.Em "line discipline" ) , 79the particular details of which is described in 80.Xr stty 1 81at the command level, and in 82.Xr termios 4 83at the programming level. 84A user may be concerned with changing 85settings associated with his particular login terminal and should refer 86to the preceding man pages for the common cases. 87The remainder of this man page is concerned 88with describing details of using and controlling terminal devices 89at a low level, such as that possibly required by a program wishing 90to provide features similar to those provided by the system. 91.Ss Line disciplines 92A terminal file is used like any other file in the system in that 93it can be opened, read, and written to using standard system 94calls. 95For each existing terminal file, there is a software processing module 96called a 97.Em "line discipline" 98is associated with it. 99The 100.Em "line discipline" 101essentially glues the low level device driver code with the high 102level generic interface routines (such as 103.Xr read 2 104and 105.Xr write 2 ) , 106and is responsible for implementing the semantics associated 107with the device. 108When a terminal file is first opened by a program, the default 109.Em "line discipline" 110called the 111.Dv termios 112line discipline is associated with the file. 113This is the primary 114line discipline that is used in most cases and provides the semantics 115that users normally associate with a terminal. 116When the 117.Dv termios 118line discipline is in effect, the terminal file behaves and is 119operated according to the rules described in 120.Xr termios 4 . 121Please refer to that man page for a full description of the terminal 122semantics. 123The operations described here 124generally represent features common 125across all 126.Em "line disciplines" , 127however some of these calls may not 128make sense in conjunction with a line discipline other than 129.Dv termios , 130and some may not be supported by the underlying 131hardware (or lack thereof, as in the case of ptys). 132.Ss Terminal File Operations 133All of the following operations are invoked using the 134.Xr ioctl 2 135system call. 136Refer to that man page for a description of the 137.Em request 138and 139.Em argp 140parameters. 141In addition to the ioctl 142.Em requests 143defined here, the specific line discipline 144in effect will define other 145.Em requests 146specific to it (actually 147.Xr termios 4 148defines them as function calls, not ioctl 149.Em requests . ) 150The following section lists the available ioctl requests. 151The name of the request, a description of its purpose, and the typed 152.Em argp 153parameter (if any) 154are listed. 155For example, the first entry says 156.Pp 157.D1 Em "TIOCSETD int *ldisc" 158.Pp 159and would be called on the terminal associated with 160file descriptor zero by the following code fragment: 161.Bd -literal 162 int ldisc; 163 164 ldisc = TTYDISC; 165 ioctl(0, TIOCSETD, &ldisc); 166.Ed 167.Ss Terminal File Request Descriptions 168.Bl -tag -width TIOCGWINSZ 169.It Dv TIOCSETD Fa int *ldisc 170Change to the new line discipline pointed to by 171.Fa ldisc . 172The available line disciplines are listed in 173.In sys/ttycom.h 174and currently are: 175.Pp 176.Bl -tag -width NETGRAPHDISC -compact 177.It TTYDISC 178Termios interactive line discipline. 179.It TABLDISC 180Tablet line discipline. 181.It SLIPDISC 182Serial IP line discipline. 183.It PPPDISC 184PPP line discipline. 185.It NETGRAPHDISC 186Netgraph 187.Xr ng_tty 4 188line discipline. 189.El 190.Pp 191.It Dv TIOCGETD Fa int *ldisc 192Return the current line discipline in the integer pointed to by 193.Fa ldisc . 194.It Dv TIOCSBRK Fa void 195Set the terminal hardware into BREAK condition. 196.It Dv TIOCCBRK Fa void 197Clear the terminal hardware BREAK condition. 198.It Dv TIOCSDTR Fa void 199Assert data terminal ready (DTR). 200.It Dv TIOCCDTR Fa void 201Clear data terminal ready (DTR). 202.It Dv TIOCGPGRP Fa int *tpgrp 203Return the current process group with which the terminal is associated 204in the integer pointed to by 205.Fa tpgrp . 206This is the underlying call that implements the 207.Xr termios 4 208.Fn tcgetattr 209call. 210.It Dv TIOCSPGRP Fa int *tpgrp 211Associate the terminal with the process group (as an integer) pointed to by 212.Fa tpgrp . 213This is the underlying call that implements the 214.Xr termios 4 215.Fn tcsetattr 216call. 217.It Dv TIOCGETA Fa struct termios *term 218Place the current value of the termios state associated with the 219device in the termios structure pointed to by 220.Fa term . 221This is the underlying call that implements the 222.Xr termios 4 223.Fn tcgetattr 224call. 225.It Dv TIOCSETA Fa struct termios *term 226Set the termios state associated with the device immediately. 227This is the underlying call that implements the 228.Xr termios 4 229.Fn tcsetattr 230call with the 231.Dv TCSANOW 232option. 233.It Dv TIOCSETAW Fa struct termios *term 234First wait for any output to complete, then set the termios state 235associated with the device. 236This is the underlying call that implements the 237.Xr termios 4 238.Fn tcsetattr 239call with the 240.Dv TCSADRAIN 241option. 242.It Dv TIOCSETAF Fa struct termios *term 243First wait for any output to complete, clear any pending input, 244then set the termios state associated with the device. 245This is the underlying call that implements the 246.Xr termios 4 247.Fn tcsetattr 248call with the 249.Dv TCSAFLUSH 250option. 251.It Dv TIOCOUTQ Fa int *num 252Place the current number of characters in the output queue in the 253integer pointed to by 254.Fa num . 255.It Dv TIOCSTI Fa char *cp 256Simulate typed input. 257Pretend as if the terminal received the character pointed to by 258.Fa cp . 259.It Dv TIOCNOTTY Fa void 260This call is obsolete but left for compatibility. 261In the past, when a process that did not have a controlling terminal (see 262.Em The Controlling Terminal 263in 264.Xr termios 4 ) 265first opened a terminal device, it acquired that terminal as its 266controlling terminal. 267For some programs this was a hazard as they 268did not want a controlling terminal in the first place, and this 269provided a mechanism to disassociate the controlling terminal from 270the calling process. 271It 272.Em must 273be called by opening the file 274.Pa /dev/tty 275and calling 276.Dv TIOCNOTTY 277on that file descriptor. 278.Pp 279The current system does not allocate a controlling terminal to 280a process on an 281.Fn open 282call: there is a specific ioctl called 283.Dv TIOSCTTY 284to make a terminal the controlling 285terminal. 286In addition, a program can 287.Fn fork 288and call the 289.Fn setsid 290system call which will place the process into its own session - which 291has the effect of disassociating it from the controlling terminal. 292This is the new and preferred method for programs to lose their controlling 293terminal. 294.It Dv TIOCSTOP Fa void 295Stop output on the terminal (like typing ^S at the keyboard). 296.It Dv TIOCSTART Fa void 297Start output on the terminal (like typing ^Q at the keyboard). 298.It Dv TIOCSCTTY Fa void 299Make the terminal the controlling terminal for the process (the process 300must not currently have a controlling terminal). 301.It Dv TIOCDRAIN Fa void 302Wait until all output is drained. 303.It Dv TIOCEXCL Fa void 304Set exclusive use on the terminal. 305No further opens are permitted except by root. 306Of course, this means that programs that are run by 307root (or setuid) will not obey the exclusive setting - which limits 308the usefulness of this feature. 309.It Dv TIOCNXCL Fa void 310Clear exclusive use of the terminal. 311Further opens are permitted. 312.It Dv TIOCFLUSH Fa int *what 313If the value of the int pointed to by 314.Fa what 315contains the 316.Dv FREAD 317bit as defined in 318.In sys/file.h , 319then all characters in the input queue are cleared. 320If it contains the 321.Dv FWRITE 322bit, then all characters in the output queue are cleared. 323If the value of the integer is zero, then it behaves as if both the 324.Dv FREAD 325and 326.Dv FWRITE 327bits were set (i.e., clears both queues). 328.It Dv TIOCGWINSZ Fa struct winsize *ws 329Put the window size information associated with the terminal in the 330.Va winsize 331structure pointed to by 332.Fa ws . 333The window size structure contains the number of rows and columns (and pixels 334if appropriate) of the devices attached to the terminal. 335It is set by user software 336and is the means by which most full\&-screen oriented programs determine the 337screen size. 338The 339.Va winsize 340structure is defined in 341.In sys/ioctl.h . 342.It Dv TIOCSWINSZ Fa struct winsize *ws 343Set the window size associated with the terminal to be the value in 344the 345.Va winsize 346structure pointed to by 347.Fa ws 348(see above). 349.It Dv TIOCCONS Fa int *on 350If 351.Fa on 352points to a non-zero integer, redirect kernel console output (kernel printf's) 353to this terminal. 354If 355.Fa on 356points to a zero integer, redirect kernel console output back to the normal 357console. 358This is usually used on workstations to redirect kernel messages 359to a particular window. 360.It Dv TIOCMSET Fa int *state 361The integer pointed to by 362.Fa state 363contains bits that correspond to modem state. 364Following is a list of defined variables and the modem state they represent: 365.Pp 366.Bl -tag -width TIOCMXCTS -compact 367.It TIOCM_LE 368Line Enable. 369.It TIOCM_DTR 370Data Terminal Ready. 371.It TIOCM_RTS 372Request To Send. 373.It TIOCM_ST 374Secondary Transmit. 375.It TIOCM_SR 376Secondary Receive. 377.It TIOCM_CTS 378Clear To Send. 379.It TIOCM_CAR 380Carrier Detect. 381.It TIOCM_CD 382Carrier Detect (synonym). 383.It TIOCM_RNG 384Ring Indication. 385.It TIOCM_RI 386Ring Indication (synonym). 387.It TIOCM_DSR 388Data Set Ready. 389.El 390.Pp 391This call sets the terminal modem state to that represented by 392.Fa state . 393Not all terminals may support this. 394.It Dv TIOCMGET Fa int *state 395Return the current state of the terminal modem lines as represented 396above in the integer pointed to by 397.Fa state . 398.It Dv TIOCMBIS Fa int *state 399The bits in the integer pointed to by 400.Fa state 401represent modem state as described above, however the state is OR-ed 402in with the current state. 403.It Dv TIOCMBIC Fa int *state 404The bits in the integer pointed to by 405.Fa state 406represent modem state as described above, however each bit which is on 407in 408.Fa state 409is cleared in the terminal. 410.El 411.Sh IMPLEMENTATION NOTES 412The total number of input and output bytes 413through all terminal devices 414are available via the 415.Va kern.tk_nin 416and 417.Va kern.tk_nout 418read-only 419.Xr sysctl 8 420variables. 421.Sh SEE ALSO 422.Xr stty 1 , 423.Xr ioctl 2 , 424.Xr ng_tty 4 , 425.Xr pty 4 , 426.Xr termios 4 , 427.Xr getty 8 428