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Neither the name of the University nor the names of its contributors 13.\" may be used to endorse or promote products derived from this software 14.\" without specific prior written permission. 15.\" 16.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 17.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 20.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26.\" SUCH DAMAGE. 27.\" 28.\" @(#)tty.4 8.3 (Berkeley) 4/19/94 29.\" $FreeBSD$ 30.\" 31.Dd December 26, 2009 32.Dt TTY 4 33.Os 34.Sh NAME 35.Nm tty 36.Nd general terminal interface 37.Sh SYNOPSIS 38.In sys/ioctl.h 39.Sh DESCRIPTION 40This section describes the interface to the terminal drivers 41in the system. 42.Ss Terminal Special Files 43Each hardware terminal port on the system usually has a terminal special device 44file associated with it in the directory ``/dev/'' (for 45example, ``/dev/tty03''). 46When a user logs into 47the system on one of these hardware terminal ports, the system has already 48opened the associated device and prepared the line for normal interactive 49use (see 50.Xr getty 8 . ) 51There is also a special case of a terminal file that connects not to 52a hardware terminal port, but to another program on the other side. 53These special terminal devices are called 54.Em ptys 55and provide the mechanism necessary to give users the same interface to the 56system when logging in over a network (using 57.Xr rlogin 1 , 58or 59.Xr telnet 1 60for example). 61Even in these cases the details of how the terminal 62file was opened and set up is already handled by special software 63in the system. 64Thus, users do not normally need to worry about the details of 65how these lines are opened or used. 66Also, these lines are often used 67for dialing out of a system (through an out-calling modem), but again 68the system provides programs that hide the details of accessing 69these terminal special files (see 70.Xr tip 1 ) . 71.Pp 72When an interactive user logs in, the system prepares the line to 73behave in a certain way (called a 74.Em "line discipline" ) , 75the particular details of which is described in 76.Xr stty 1 77at the command level, and in 78.Xr termios 4 79at the programming level. 80A user may be concerned with changing 81settings associated with his particular login terminal and should refer 82to the preceding man pages for the common cases. 83The remainder of this man page is concerned 84with describing details of using and controlling terminal devices 85at a low level, such as that possibly required by a program wishing 86to provide features similar to those provided by the system. 87.Ss Terminal File Operations 88All of the following operations are invoked using the 89.Xr ioctl 2 90system call. 91Refer to that man page for a description of the 92.Em request 93and 94.Em argp 95parameters. 96In addition to the ioctl 97.Em requests 98defined here, the specific line discipline 99in effect will define other 100.Em requests 101specific to it (actually 102.Xr termios 4 103defines them as function calls, not ioctl 104.Em requests . ) 105The following section lists the available ioctl requests. 106The name of the request, a description of its purpose, and the typed 107.Em argp 108parameter (if any) 109are listed. 110For example, the first entry says 111.Pp 112.D1 Em "TIOCSPGRP int *tpgrp" 113.Pp 114and would be called on the terminal associated with 115file descriptor zero by the following code fragment: 116.Bd -literal 117 int pgrp; 118 119 pgrp = getpgrp(); 120 ioctl(0, TIOCSPGRP, &pgrp); 121.Ed 122.Ss Terminal File Request Descriptions 123.Bl -tag -width TIOCGWINSZ 124.It Dv TIOCSETD Fa int *ldisc 125This call is obsolete but left for compatibility. 126Before 127.Fx 8.0 , 128it would change to the new line discipline pointed to by 129.Fa ldisc . 130.It Dv TIOCGETD Fa int *ldisc 131Return the current line discipline in the integer pointed to by 132.Fa ldisc . 133.It Dv TIOCSBRK Fa void 134Set the terminal hardware into BREAK condition. 135.It Dv TIOCCBRK Fa void 136Clear the terminal hardware BREAK condition. 137.It Dv TIOCSDTR Fa void 138Assert data terminal ready (DTR). 139.It Dv TIOCCDTR Fa void 140Clear data terminal ready (DTR). 141.It Dv TIOCGPGRP Fa int *tpgrp 142Return the current process group with which the terminal is associated 143in the integer pointed to by 144.Fa tpgrp . 145This is the underlying call that implements the 146.Xr termios 4 147.Fn tcgetattr 148call. 149.It Dv TIOCSPGRP Fa int *tpgrp 150Associate the terminal with the process group (as an integer) pointed to by 151.Fa tpgrp . 152This is the underlying call that implements the 153.Xr termios 4 154.Fn tcsetattr 155call. 156.It Dv TIOCGETA Fa struct termios *term 157Place the current value of the termios state associated with the 158device in the termios structure pointed to by 159.Fa term . 160This is the underlying call that implements the 161.Xr termios 4 162.Fn tcgetattr 163call. 164.It Dv TIOCSETA Fa struct termios *term 165Set the termios state associated with the device immediately. 166This is the underlying call that implements the 167.Xr termios 4 168.Fn tcsetattr 169call with the 170.Dv TCSANOW 171option. 172.It Dv TIOCSETAW Fa struct termios *term 173First wait for any output to complete, then set the termios state 174associated with the device. 175This is the underlying call that implements the 176.Xr termios 4 177.Fn tcsetattr 178call with the 179.Dv TCSADRAIN 180option. 181.It Dv TIOCSETAF Fa struct termios *term 182First wait for any output to complete, clear any pending input, 183then set the termios state associated with the device. 184This is the underlying call that implements the 185.Xr termios 4 186.Fn tcsetattr 187call with the 188.Dv TCSAFLUSH 189option. 190.It Dv TIOCOUTQ Fa int *num 191Place the current number of characters in the output queue in the 192integer pointed to by 193.Fa num . 194.It Dv TIOCSTI Fa char *cp 195Simulate typed input. 196Pretend as if the terminal received the character pointed to by 197.Fa cp . 198.It Dv TIOCNOTTY Fa void 199This call is obsolete but left for compatibility. 200In the past, when a process that did not have a controlling terminal (see 201.Em The Controlling Terminal 202in 203.Xr termios 4 ) 204first opened a terminal device, it acquired that terminal as its 205controlling terminal. 206For some programs this was a hazard as they 207did not want a controlling terminal in the first place, and this 208provided a mechanism to disassociate the controlling terminal from 209the calling process. 210It 211.Em must 212be called by opening the file 213.Pa /dev/tty 214and calling 215.Dv TIOCNOTTY 216on that file descriptor. 217.Pp 218The current system does not allocate a controlling terminal to 219a process on an 220.Fn open 221call: there is a specific ioctl called 222.Dv TIOCSCTTY 223to make a terminal the controlling 224terminal. 225In addition, a program can 226.Fn fork 227and call the 228.Fn setsid 229system call which will place the process into its own session - which 230has the effect of disassociating it from the controlling terminal. 231This is the new and preferred method for programs to lose their controlling 232terminal. 233.It Dv TIOCSTOP Fa void 234Stop output on the terminal (like typing ^S at the keyboard). 235.It Dv TIOCSTART Fa void 236Start output on the terminal (like typing ^Q at the keyboard). 237.It Dv TIOCSCTTY Fa void 238Make the terminal the controlling terminal for the process (the process 239must not currently have a controlling terminal). 240.It Dv TIOCDRAIN Fa void 241Wait until all output is drained. 242.It Dv TIOCEXCL Fa void 243Set exclusive use on the terminal. 244No further opens are permitted except by root. 245Of course, this means that programs that are run by 246root (or setuid) will not obey the exclusive setting - which limits 247the usefulness of this feature. 248.It Dv TIOCNXCL Fa void 249Clear exclusive use of the terminal. 250Further opens are permitted. 251.It Dv TIOCFLUSH Fa int *what 252If the value of the int pointed to by 253.Fa what 254contains the 255.Dv FREAD 256bit as defined in 257.In sys/file.h , 258then all characters in the input queue are cleared. 259If it contains the 260.Dv FWRITE 261bit, then all characters in the output queue are cleared. 262If the value of the integer is zero, then it behaves as if both the 263.Dv FREAD 264and 265.Dv FWRITE 266bits were set (i.e., clears both queues). 267.It Dv TIOCGWINSZ Fa struct winsize *ws 268Put the window size information associated with the terminal in the 269.Va winsize 270structure pointed to by 271.Fa ws . 272The window size structure contains the number of rows and columns (and pixels 273if appropriate) of the devices attached to the terminal. 274It is set by user software 275and is the means by which most full\&-screen oriented programs determine the 276screen size. 277The 278.Va winsize 279structure is defined in 280.In sys/ioctl.h . 281.It Dv TIOCSWINSZ Fa struct winsize *ws 282Set the window size associated with the terminal to be the value in 283the 284.Va winsize 285structure pointed to by 286.Fa ws 287(see above). 288.It Dv TIOCCONS Fa int *on 289If 290.Fa on 291points to a non-zero integer, redirect kernel console output (kernel printf's) 292to this terminal. 293If 294.Fa on 295points to a zero integer, redirect kernel console output back to the normal 296console. 297This is usually used on workstations to redirect kernel messages 298to a particular window. 299.It Dv TIOCMSET Fa int *state 300The integer pointed to by 301.Fa state 302contains bits that correspond to modem state. 303Following is a list of defined variables and the modem state they represent: 304.Pp 305.Bl -tag -width TIOCMXCTS -compact 306.It TIOCM_LE 307Line Enable. 308.It TIOCM_DTR 309Data Terminal Ready. 310.It TIOCM_RTS 311Request To Send. 312.It TIOCM_ST 313Secondary Transmit. 314.It TIOCM_SR 315Secondary Receive. 316.It TIOCM_CTS 317Clear To Send. 318.It TIOCM_CAR 319Carrier Detect. 320.It TIOCM_CD 321Carrier Detect (synonym). 322.It TIOCM_RNG 323Ring Indication. 324.It TIOCM_RI 325Ring Indication (synonym). 326.It TIOCM_DSR 327Data Set Ready. 328.El 329.Pp 330This call sets the terminal modem state to that represented by 331.Fa state . 332Not all terminals may support this. 333.It Dv TIOCMGET Fa int *state 334Return the current state of the terminal modem lines as represented 335above in the integer pointed to by 336.Fa state . 337.It Dv TIOCMBIS Fa int *state 338The bits in the integer pointed to by 339.Fa state 340represent modem state as described above, however the state is OR-ed 341in with the current state. 342.It Dv TIOCMBIC Fa int *state 343The bits in the integer pointed to by 344.Fa state 345represent modem state as described above, however each bit which is on 346in 347.Fa state 348is cleared in the terminal. 349.El 350.Sh IMPLEMENTATION NOTES 351The total number of input and output bytes 352through all terminal devices 353are available via the 354.Va kern.tk_nin 355and 356.Va kern.tk_nout 357read-only 358.Xr sysctl 8 359variables. 360.Sh SEE ALSO 361.Xr stty 1 , 362.Xr ioctl 2 , 363.Xr ng_tty 4 , 364.Xr pty 4 , 365.Xr termios 4 , 366.Xr getty 8 367