1pty(7D) Devices pty(7D)
2
6 pty - pseudo-terminal driver
7
9 The pty driver provides support for a pair of devices collectively
10 known as a pseudo-terminal. The two devices comprising a pseudo-termi‐
11 nal are known as a controller and a slave. The slave device distin‐
12 guishes between the B0 baud rate and other baud rates specified in the
13 c_cflag word of the termios structure, and the CLOCAL flag in that
14 word. It does not support any of the other termio(7I) device control
15 functions specified by flags in the c_cflag word of the termios struc‐
16 ture and by the IGNBRK, IGNPAR, PARMRK, or INPCK flags in the
17 c_iflag word of the termios structure, as these functions apply only to
18 asynchronous serial ports. All other termio(7I) functions must be per‐
19 formed by STREAMS modules pushed atop the driver; when a slave device
20 is opened, the ldterm(7M) and ttcompat(7M) STREAMS modules are automat‐
21 ically pushed on top of the stream, providing the standard termio(7I)
22 interface.
23 Instead of having a hardware interface and associated hardware that
26 supports the terminal functions, the functions are implemented by
27 another process manipulating the controller device of the pseudo-termi‐
28 nal.
29 The controller and the slave devices of the pseudo-terminal are tightly
32 connected. Any data written on the controller device is given to the
33 slave device as input, as though it had been received from a hardware
34 interface. Any data written on the slave terminal can be read from the
35 controller device (rather than being transmitted from a UAR).
36 By default, 48 pseudo-terminal pairs are configured as follows:
39 /dev/pty[p-r][0-9a-f] controller devices
41 /dev/tty[p-r][0-9a-f] slave devices
42
45 The standard set of termio ioctls are supported by the slave device.
46 None of the bits in the c_cflag word have any effect on the pseudo-ter‐
47 minal, except that if the baud rate is set to B0, it will appear to the
48 process on the controller device as if the last process on the slave
49 device had closed the line; thus, setting the baud rate to B0 has the
50 effect of ``hanging up'' the pseudo-terminal, just as it has the effect
51 of ``hanging up'' a real terminal.
52 There is no notion of ``parity'' on a pseudo-terminal, so none of the
55 flags in the c_iflag word that control the processing of parity errors
56 have any effect. Similarly, there is no notion of a ``break'', so none
57 of the flags that control the processing of breaks, and none of the
58 ioctls that generate breaks, have any effect.
59 Input flow control is automatically performed; a process that attempts
62 to write to the controller device will be blocked if too much uncon‐
63 sumed data is buffered on the slave device. The input flow control
64 provided by the IXOFF flag in the c_iflag word is not supported.
65 The delays specified in the c_oflag word are not supported.
68 As there are no modems involved in a pseudo-terminal, the ioctls that
71 return or alter the state of modem control lines are silently ignored.
72 A few special ioctls are provided on the controller devices of pseudo-
75 terminals to provide the functionality needed by applications programs
76 to emulate real hardware interfaces:
77 TIOCSTOP The argument is ignored. Output to the pseudo-terminal is
79 suspended, as if a STOP character had been typed.
80 TIOCSTART The argument is ignored. Output to the pseudo-terminal is
83 restarted, as if a START character had been typed.
84 TIOCPKT The argument is a pointer to an int. If the value of the
87 int is non-zero, packet mode is enabled; if the value of
88 the int is zero, packet mode is disabled. When a pseudo-
89 terminal is in packet mode, each subsequent read(2) from
90 the controller device will return data written on the
91 slave device preceded by a zero byte (symbolically
92 defined as TIOCPKT_DATA), or a single byte reflecting
93 control status information. In the latter case, the byte
94 is an inclusive-or of zero or more of the bits:
95 TIOCPKT_FLUSHREAD whenever the read queue for the
97 terminal is flushed.
98 TIOCPKT_FLUSHWRITE whenever the write queue for the
101 terminal is flushed.
102 TIOCPKT_STOP whenever output to the terminal is
105 stopped using ^S.
106 TIOCPKT_START whenever output to the terminal is
109 restarted.
110 TIOCPKT_DOSTOP whenever XON/XOFF flow control is
113 enabled after being disabled; it is
114 considered ``enabled'' when the
115 IXON flag in the c_iflag word is
116 set, the VSTOP member of the c_cc
117 array is ^S and the VSTART member
118 of the c_cc array is ^Q.
119 TIOCPKT_NOSTOP whenever XON/XOFF flow control is
122 disabled after being enabled.
123 TIOCREMOTE The argument is a pointer to an int. If the value of the
127 int is non-zero, remote mode is enabled; if the value of
128 the int is zero, remote mode is disabled. This mode can
129 be enabled or disabled independently of packet mode. When
130 a pseudo-terminal is in remote mode, input to the slave
131 device of the pseudo-terminal is flow controlled and not
132 input edited (regardless of the mode the slave side of
133 the pseudo-terminal). Each write to the controller device
134 produces a record boundary for the process reading the
135 slave device. In normal usage, a write of data is like
136 the data typed as a line on the terminal; a write of 0
137 bytes is like typing an EOF character. Note: this means
138 that a process writing to a pseudo-terminal controller in
139 remote mode must keep track of line boundaries, and write
140 only one line at a time to the controller. If, for exam‐
141 ple, it were to buffer up several NEWLINE characters and
142 write them to the controller with one write(), it would
143 appear to a process reading from the slave as if a single
144 line containing several NEWLINE characters had been typed
145 (as if, for example, a user had typed the LNEXT character
146 before typing all but the last of those NEWLINE charac‐
147 ters). Remote mode can be used when doing remote line
148 editing in a window manager, or whenever flow controlled
149 input is required.
150
153 #include <fcntl.h>
154 #include <sys/termios.h>
155 int fdm fds;
157 fdm = open("/dev/ptyp0, O_RDWR); /* open master */
158 fds = open("/dev/ttyp0, O_RDWR); /* open slave */
159
162 /dev/pty[p-z][0-9a-f] pseudo-terminal controller devices
163 /dev/tty[p-z][0-9a-f] pseudo-terminal slave devices
166
169 rlogin(1), rlogind(1M), ldterm(7M), termio(7I), ttcompat(7M),
170
172 It is apparently not possible to send an EOT by writing zero bytes in
173 TIOCREMOTE mode.
174SunOS 5.11 8 Aug 1994 pty(7D)