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TTY(4) UNIX Programmer's Manual TTY(4) NNAAMMEE ttttyy - general terminal interface SSYYNNOOPPSSIISS ##iinncclluuddee <<ssyyss//iiooccttll..hh>> DDEESSCCRRIIPPTTIIOONN This section describes the interface to the terminal drivers in the sys- tem. TTeerrmmiinnaall SSppeecciiaall FFiilleess Each hardware terminal port on the system usually has a terminal special device file associated with it in the directory ``/dev/'' (for example, ``/dev/tty03''). When a user logs into the system on one of these hard- ware terminal ports, the system has already opened the associated device and prepared the line for normal interactive use (see getty(8).) There is also a special case of a terminal file that connects not to a hardware terminal port, but to another program on the other side. These special terminal devices are called _p_t_y_s and provide the mechanism necessary to give users the same interface to the system when logging in over a net- work (using rlogin(1), or telnet(1) for example.) Even in these cases the details of how the terminal file was opened and set up is already handled by special software in the system. Thus, users do not normally need to worry about the details of how these lines are opened or used. Also, these lines are often used for dialing out of a system (through an out-calling modem), but again the system provides programs that hide the details of accessing these terminal special files (see tip(2).) When an interactive user logs in, the system prepares the line to behave in a certain way (called a _l_i_n_e _d_i_s_c_i_p_l_i_n_e), the particular details of which is described in stty(1) at the command level, and in termios(4) at the programming level. A user may be concerned with changing settings associated with his particular login terminal and should refer to the preceding man pages for the common cases. The remainder of this man page is concerned with describing details of using and controlling terminal devices at a low level, such as that possibly required by a program wish- ing to provide features similar to those provided by the system. LLiinnee ddiisscciipplliinneess A terminal file is used like any other file in the system in that it can be opened, read, and written to using standard system calls. For each existing terminal file, there is a software processing module called a _l_i_n_e _d_i_s_c_i_p_l_i_n_e is associated with it. The _l_i_n_e _d_i_s_c_i_p_l_i_n_e essentially glues the low level device driver code with the high level generic inter- face routines (such as read(2) and write(2)), and is responsible for im- plementing the semantics associated with the device. When a terminal file is first opened by a program, the default _l_i_n_e _d_i_s_c_i_p_l_i_n_e called the termios line discipline is associated with the file. This is the primary line discipline that is used in most cases and provides the semantics that users normally associate with a terminal. When the termios line discipline is in effect, the terminal file behaves and is operated ac- cording to the rules described in termios(4). Please refer to that man page for a full description of the terminal semantics. The operations described here generally represent features common across all _l_i_n_e _d_i_s_c_i_p_l_i_n_e_s, however some of these calls may not make sense in conjunc- tion with a line discipline other than termios, and some may not be sup- ported by the underlying hardware (or lack thereof, as in the case of ptys). TTeerrmmiinnaall FFiillee OOppeerraattiioonnss All of the following operations are invoked using the ioctl(2) system call. Refer to that man page for a description of the _r_e_q_u_e_s_t and _a_r_g_p parameters. In addition to the ioctl _r_e_q_u_e_s_t_s defined here, the specific line discipline in effect will define other _r_e_q_u_e_s_t_s specific to it (ac- tually termios(4) defines them as function calls, not ioctl _r_e_q_u_e_s_t_s.) The following section lists the available ioctl requests. The name of the request, a description of its purpose, and the typed _a_r_g_p parameter (if any) are listed. For example, the first entry says _T_I_O_C_S_E_T_D _i_n_t _*_l_d_i_s_c and would be called on the terminal associated with file descriptor zero by the following code fragment: int ldisc; ldisc = TTYDISC; ioctl(0, TIOCSETD, &ldisc); TTeerrmmiinnaall FFiillee RReeqquueesstt DDeessccrriippttiioonnss TIOCSETD _i_n_t _*_l_d_i_s_c Change to the new line discipline pointed to by _l_d_i_s_c. The available line disciplines are listed in <sys/termios.h> and currently are: TTYDISC Termios interactive line discipline. TABLDISC Tablet line discipline. SLIPDISC Serial IP line discipline. TIOCGETD _i_n_t _*_l_d_i_s_c Return the current line discipline in the integer pointed to by _l_d_i_s_c. TIOCSBRK _v_o_i_d Set the terminal hardware into BREAK condition. TIOCCBRK _v_o_i_d Clear the terminal hardware BREAK condition. TIOCSDTR _v_o_i_d Assert data terminal ready (DTR). TIOCCDTR _v_o_i_d Clear data terminal ready (DTR). TIOCGPGRP _i_n_t _*_t_p_g_r_p Return the current process group the terminal is associated with in the integer pointed to by _t_p_g_r_p. This is the underly- ing call that implements the termios(4) ttccggeettaattttrr() call. TIOCSPGRP _i_n_t _*_t_p_g_r_p Associate the terminal with the process group (as an integer) pointed to by _t_p_g_r_p. This is the underlying call that imple- ments the termios(4) ttccsseettaattttrr() call. TIOCGETA _s_t_r_u_c_t _t_e_r_m_i_o_s _*_t_e_r_m Place the current value of the termios state associated with the device in the termios structure pointed to by _t_e_r_m. This is the underlying call that implements the termios(4) ttccggeettaattttrr() call. TIOCSETA _s_t_r_u_c_t _t_e_r_m_i_o_s _*_t_e_r_m Set the termios state associated with the device immediately. This is the underlying call that implements the termios(4) ttccsseettaattttrr() call with the TCSANOW option. TIOCSETAW _s_t_r_u_c_t _t_e_r_m_i_o_s _*_t_e_r_m First wait for any output to complete, then set the termios state associated with the device. This is the underlying call that implements the termios(4) ttccsseettaattttrr() call with the TCSADRAIN option. TIOCSETAF _s_t_r_u_c_t _t_e_r_m_i_o_s _*_t_e_r_m First wait for any output to complete, clear any pending in- put, then set the termios state associated with the device. This is the underlying call that implements the termios(4) ttccsseettaattttrr() call with the TCSAFLUSH option. TIOCOUTQ _i_n_t _*_n_u_m Place the current number of characters in the output queue in the integer pointed to by _n_u_m. TIOCSTI _c_h_a_r _*_c_p Simulate typed input. Pretend as if the terminal received the character pointed to by _c_p. TIOCNOTTY _v_o_i_d This call is obsolete but left for compatibility. In the past, when a process that didn't have a controlling terminal (see _T_h_e _C_o_n_t_r_o_l_l_i_n_g _T_e_r_m_i_n_a_l in termios(4)) first opened a terminal device, it acquired that terminal as its controlling terminal. For some programs this was a hazard as they didn't want a controlling terminal in the first place, and this pro- vided a mechanism to disassociate the controlling terminal from the calling process. It _m_u_s_t be called by opening the file _/_d_e_v_/_t_t_y and calling TIOCNOTTY on that file descriptor. The current system does not allocate a controlling terminal to a process on an ooppeenn() call: there is a specific ioctl called TIOSCTTY to make a terminal the controlling terminal. In addition, a program can ffoorrkk() and call the sseettssiidd() sys- tem call which will place the process into its own session - which has the effect of disassociating it from the control- ling terminal. This is the new and preferred method for pro- grams to lose their controlling terminal. TIOCSTOP _v_o_i_d Stop output on the terminal (like typing ^S at the keyboard). TIOCSTART _v_o_i_d Start output on the terminal (like typing ^Q at the key- board). TIOCSCTTY _v_o_i_d Make the terminal the controlling terminal for the process (the process must not currently have a controlling terminal). TIOCDRAIN _v_o_i_d Wait until all output is drained. TIOCEXCL _v_o_i_d Set exclusive use on the terminal. No further opens are per- mitted except by root. Of course, this means that programs that are run by root (or setuid) will not obey the exclusive setting - which limits the usefulness of this feature. TIOCNXCL _v_o_i_d Clear exclusive use of the terminal. Further opens are per- mitted. TIOCFLUSH _i_n_t _*_w_h_a_t If the value of the int pointed to by _w_h_a_t contains the FREAD bit as defined in <sys/file.h>, then all characters in the input queue are cleared. If it contains the FWRITE bit, then all characters in the output queue are cleared. If the value of the integer is zero, then it behaves as if both the FREAD and FWRITE bits were set (i.e. clears both queues). TIOCGWINSZ _s_t_r_u_c_t _w_i_n_s_i_z_e _*_w_s Put the window size information associated with the terminal in the _w_i_n_s_i_z_e structure pointed to by _w_s. The window size structure contains the number of rows and columns (and pixels if appropriate) of the devices attached to the terminal. It is set by user software and is the means by which most full- screen oriented programs determine the screen size. The _w_i_n_s_i_z_e structure is defined in <sys/ioctl.h>. TIOCSWINSZ _s_t_r_u_c_t _w_i_n_s_i_z_e _*_w_s Set the window size associated with the terminal to be the value in the _w_i_n_s_i_z_e structure pointed to by _w_s (see above). TIOCCONS _i_n_t _*_o_n If _o_n points to a non-zero integer, redirect kernel console output (kernel printf's) to this terminal. If _o_n points to a zero integer, redirect kernel console output back to the nor- mal console. This is usually used on workstations to redi- rect kernel messages to a particular window. TIOCMSET _i_n_t _*_s_t_a_t_e The integer pointed to by _s_t_a_t_e contains bits that correspond to modem state. Following is a list of defined variables and the modem state they represent: TIOCM_LE Line Enable. TIOCM_DTR Data Terminal Ready. TIOCM_RTS Request To Send. TIOCM_ST Secondary Transmit. TIOCM_SR Secondary Receive. TIOCM_CTS Clear To Send. TIOCM_CAR Carrier Detect. TIOCM_CD Carier Detect (synonym). TIOCM_RNG Ring Indication. TIOCM_RI Ring Indication (synonym). TIOCM_DSR Data Set Ready. This call sets the terminal modem state to that represented by _s_t_a_t_e. Not all terminals may support this. TIOCMGET _i_n_t _*_s_t_a_t_e Return the current state of the terminal modem lines as rep- resented above in the integer pointed to by _s_t_a_t_e. TIOCMBIS _i_n_t _*_s_t_a_t_e The bits in the integer pointed to by _s_t_a_t_e represent modem state as described above, however the state is OR-ed in with the current state. TIOCMBIC _i_n_t _*_s_t_a_t_e The bits in the integer pointed to by _s_t_a_t_e represent modem state as described above, however each bit which is on in _s_t_a_t_e is cleared in the terminal. SSEEEE AALLSSOO getty(8), ioctl(2), pty(4), stty(1), termios(4) 4th Berkeley Distribution August 14, 1992 4