1.\" Copyright (c) 1991, 1992, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" %sccs.include.redist.roff% 5.\" 6.\" @(#)tty.4 8.1 (Berkeley) 06/05/93 7.\" 8.Dd August 14, 1992 9.Dt TTY 4 10.Os BSD 4 11.Sh NAME 12.Nm tty 13.Nd general terminal interface 14.Sh SYNOPSIS 15.Fd #include <sys/ioctl.h> 16.Sh DESCRIPTION 17This section describes the interface to the terminal drivers 18in the system. 19.Ss Terminal Special Files 20Each hardware terminal port on the system usually has a terminal special device 21file associated with it in the directory ``/dev/'' (for 22example, ``/dev/tty03''). 23When a user logs into 24the system on one of these hardware terminal ports, the system has already 25opened the associated device and prepared the line for normal interactive 26use (see 27.Xr getty 8 .) 28There is also a special case of a terminal file that connects not to 29a hardware terminal port, but to another program on the other side. 30These special terminal devices are called 31.Em ptys 32and provide the mechanism necessary to give users the same interface to the 33system when logging in over a network (using 34.Xr rlogin 1 , 35or 36.Xr telnet 1 37for example.) Even in these cases the details of how the terminal 38file was opened and set up is already handled by special software 39in the system. 40Thus, users do not normally need to worry about the details of 41how these lines are opened or used. Also, these lines are often used 42for dialing out of a system (through an out-calling modem), but again 43the system provides programs that hide the details of accessing 44these terminal special files (see 45.Xr tip 2 .) 46.Pp 47When an interactive user logs in, the system prepares the line to 48behave in a certain way (called a 49.Em "line discipline" ), 50the particular details of which is described in 51.Xr stty 1 52at the command level, and in 53.Xr termios 4 54at the programming level. A user may be concerned with changing 55settings associated with his particular login terminal and should refer 56to the preceding man pages for the common cases. The remainder of 57this man page is concerned 58with describing details of using and controlling terminal devices 59at a low level, such as that possibly required by a program wishing 60to provide features similar to those provided by the system. 61.Ss Line disciplines 62A terminal file is used like any other file in the system in that 63it can be opened, read, and written to using standard system 64calls. For each existing terminal file, a software processing module 65called a 66.Em "line discipline" 67is associated with it. The 68.Em "line discipline" 69essentially glues the low level device driver code with the high 70level generic interface routines (such as 71.Xr read 2 72and 73.Xr write 2 ), 74and is responsible for implementing the semantics associated 75with the device. When a terminal file is first opened by a program, 76the default 77.Em "line discipline" 78called the 79.Dv termios 80line discipline is associated with the file. This is the primary 81line discipline that is used in most cases and provides the semantics 82that users normally associate with a terminal. When the 83.Dv termios 84line discipline is in effect, the terminal file behaves and is 85operated according to the rules described in 86.Xr termios 4 . 87Please refer to that man page for a full description of the terminal 88semantics. 89The operations described here 90generally represent features common 91across all 92.Em "line disciplines" 93however, some of these calls may not 94make sense in conjunction with a line discipline other than 95.Dv termios , 96and some may not be supported by the underlying 97hardware or (lack thereof, as in the case of ptys). 98.Ss Terminal File Operations 99All of the following operations are invoked using the 100.Xr ioctl 2 101system call. Refer to that man page for a description of 102the 103.Em request 104and 105.Em argp 106parameter. 107In addition to the ioctl 108.Em requests 109defined here, the specific line discipline 110in effect will define other 111.Em requests 112specific to it (actually 113.Xr termios 4 114defines them as function calls, not ioctl 115.Em requests .) 116The following section lists the available ioctl requests. The 117name of the request and the typed 118.Em argp 119parameter (if any) 120is listed along with a description of its 121purpose. For example, the first entry says 122.Pp 123.D1 Em "TIOCSETD int *ldisc" 124.Pp 125and would be called on the terminal associated with 126file discriptor zero by the following code fragment: 127.Bd -literal 128 int ldisc; 129 130 ldisc = TTYDISC; 131 ioctl(0, TIOCSETD, &ldisc); 132.Ed 133.Ss Terminal File Request Descriptions 134.Bl -tag -width TIOCGWINSZ 135.It Dv TIOCSETD Fa int *ldisc 136Change to the new line discipline pointed to by 137.Fa ldisc . 138The available line disciplines are listed in 139.Pa Aq sys/termios.h 140and currently are: 141.Pp 142.Bl -tag -width TIOCGWINSZ -compact 143.It TTYDISC 144Termios interactive line discipline. 145.It TABLDISC 146Tablet line discipline. 147.It SLIPDISC 148Serial IP line discipline. 149.El 150.Pp 151.It Dv TIOCGETD Fa int *ldisc 152Return the current line discipline in the integer pointed to by 153.Fa ldisc . 154.It Dv TIOCSBRK Fa void 155Set the terminal hardware into BREAK condition. 156.It Dv TIOCCBRK Fa void 157Clear the terminal hardware BREAK condition. 158.It Dv TIOCSDTR Fa void 159Assert data terminal ready (DTR). 160.It Dv TIOCCDTR Fa void 161Clear data terminal ready (DTR). 162.It Dv TIOCGPGRP Fa int *tpgrp 163Return the current process group the terminal is associated 164with in the integer pointed to by 165.Fa tpgrp . 166This is the underlying call that implements the 167.Xr termios 4 168.Fn tcgetattr 169call. 170.It Dv TIOCSPGRP Fa int *tpgrp 171Associate the terminal with the process group (as an integer) pointed to by 172.Fa tpgrp . 173This is the underlying call that implements the 174.Xr termios 4 175.Fn tcsetattr 176call. 177.It Dv TIOCGETA Fa struct termios *term 178Place the current value of the termios state associated with the 179device in the termios structure pointed to by 180.Fa term . 181This is the underlying call that implements the 182.Xr termios 4 183.Fn tcgetattr 184call. 185.It Dv TIOCSETA Fa struct termios *term 186Set the termios state associated with the device immediatly. 187This is the underlying call that implements the 188.Xr termios 4 189.Fn tcsetattr 190call with the 191.Dv TCSANOW 192option. 193.It Dv TIOCSETAW Fa struct termios *term 194First wait for any output to complete, then set the termios state 195associated with the device. 196This is the underlying call that implements the 197.Xr termios 4 198.Fn tcsetattr 199call with the 200.Dv TCSADRAIN 201option. 202.It Dv TIOCSETAF Fa struct termios *term 203First wait for any output to complete, clear any pending input, 204then set the termios state associated with the device. 205This is the underlying call that implements the 206.Xr termios 4 207.Fn tcsetattr 208call with the 209.Dv TCSAFLUSH 210option. 211.It Dv TIOCOUTQ Fa int *num 212Place the current number of characters in the output queue in the 213integer pointed to by 214.Fa num . 215.It Dv TIOCSTI Fa char *cp 216Simulate typed input. Pretend as if the terminal recieved the 217character pointed to by 218.Fa cp . 219.It Dv TIOCNOTTY Fa void 220This call is obsolete but left for compatability. In the past, when 221a process that didn't have a controlling terminal (see 222.Em The Controlling Terminal 223in 224.Xr termios 4 ) 225first opened a terminal device, it acquired that terminal as its 226controlling terminal. For some programs this was a hazard as they 227didn't want a controlling terminal in the first place, and this 228provided a mechanism to disassociate the controlling terminal from 229the calling process. It 230.Em must 231be called by opening the file 232.Pa /dev/tty 233and calling 234.Dv TIOCNOTTY 235on that file descriptor. 236.Pp 237The current system does not allocate a controlling terminal to 238a process on an 239.Fn open 240call: there is a specific ioctl called 241.Dv TIOSCTTY 242to make a terminal the controlling 243terminal. 244In addition, a program can 245.Fn fork 246and call the 247.Fn setsid 248system call which will place the process into its own session - which 249has the effect of disassociating it from the controlling terminal. This 250is the new and prefered method for programs to lose their controlling 251terminal. 252.It Dv TIOCSTOP Fa void 253Stop output on the terminal (like typing ^S at the keyboard). 254.It Dv TIOCSTART Fa void 255Start output on the terminal (like typing ^Q at the kayboard). 256.It Dv TIOCSCTTY Fa void 257Make the terminal the controlling terminal for the process (the process 258must not currently have a controlling terminal). 259.It Dv TIOCDRAIN Fa void 260Wait until all output is drained. 261.It Dv TIOCEXCL Fa void 262Set exclusive use on the terminal. No further opens are permitted 263except by root. Of course, this means that programs that are run by 264root (or setuid) will not obey the exclusive setting - which limits 265the usefullness of this feature. 266.It Dv TIOCNXCL Fa void 267Clear exclusive use of the terminal. Further opens are permitted. 268.It Dv TIOCFLUSH Fa int *what 269If the value of the int pointed to by 270.Fa what 271contains the 272.Dv FREAD 273bit as defined in 274.Pa Aq sys/file.h , 275then all characters in the input queue are cleared. If it contains 276the 277.Dv FWRITE 278bit, then all characters in the output queue are cleared. If the 279value of the integer is zero, then it behaves as if both the 280.Dv FREAD 281and 282.Dv FWRITE 283bits were set (i.e. clears both queues). 284.It Dv TIOCGWINSZ Fa struct winsize *ws 285Put the window size information associated with the terminal in the 286.Va winsize 287structure pointed to by 288.Fa ws . 289The window size structure contains the number of rows and columns (and pixels 290if appropiate) of the devices attached to the terminal. It is set by user software 291and is the means by which most full\&-screen oriented programs determine the 292screen size. The 293.Va winsize 294structure is defined in 295.Pa Aq sys/ioctl.h . 296.It Dv TIOCSWINSZ Fa struct winsize *ws 297Set the window size associated with the terminal to be the value in 298the 299.Va winsize 300structure pointed to by 301.Fa ws 302(see above). 303.It Dv TIOCCONS Fa int *on 304If 305.Fa on 306points to a non-zero integer, redirect kernel console output (kernel printf's) 307to this terminal. 308If 309.Fa on 310points to a zero integer, redirect kernel console output back to the normal 311console. This is usually used on workstations to redirect kernel messages 312to a particular window. 313.It Dv TIOCMSET Fa int *state 314The integer pointed to by 315.Fa state 316contains bits that correspond to modem state. Following is a list 317of defined variables and the modem state they represent: 318.Pp 319.Bl -tag -width TIOCMXCTS -compact 320.It TIOCM_LE 321Line Enable. 322.It TIOCM_DTR 323Data Terminal Ready. 324.It TIOCM_RTS 325Request To Send. 326.It TIOCM_ST 327Secondary Transmit. 328.It TIOCM_SR 329Secondary Recieve. 330.It TIOCM_CTS 331Clear To Send. 332.It TIOCM_CAR 333Carrier Detect. 334.It TIOCM_CD 335Carier Detect (synonym). 336.It TIOCM_RNG 337Ring Indication. 338.It TIOCM_RI 339Ring Indication (synonym). 340.It TIOCM_DSR 341Data Set Ready. 342.El 343.Pp 344This call sets the terminal modem state to that represented by 345.Fa state . 346Not all terminals may support this. 347.It Dv TIOCMGET Fa int *state 348Return the current state of the terminal modem lines as represented 349above in the integer pointed to by 350.Fa state . 351.It Dv TIOCMBIS Fa int *state 352The bits in the integer pointed to by 353.Fa state 354represent modem state as described above, however the state is OR-ed 355in with the current state. 356.It Dv TIOCMBIC Fa int *state 357The bits in the integer pointed to by 358.Fa state 359represent modem state as described above, however each bit which is on 360in 361.Fa state 362is cleared in the terminal. 363.El 364.Sh SEE ALSO 365.Xr getty 8 , 366.Xr ioctl 2 , 367.Xr pty 4 , 368.Xr stty 1 , 369.Xr termios 4 370