1PTY(4) Kernel Interfaces Manual PTY(4)
2
6 pty - pseudo terminal driver
7
9 /sys/conf/SYSTEM:
10 NPTY ptys # pseudo-terminals, in groups of 8
11
13 The pty driver provides support for a device-pair termed a pseudo ter‐
14 minal. A pseudo terminal is a pair of character devices, a master
15 device and a slave device. The slave device provides processes an
16 interface identical to that described in tty(4). However, whereas all
17 other devices which provide the interface described in tty(4) have a
18 hardware device of some sort behind them, the slave device has,
19 instead, another process manipulating it through the master half of the
20 pseudo terminal. That is, anything written on the master device is
21 given to the slave device as input and anything written on the slave
22 device is presented as input on the master device.
23 In configuring, ptys specifies the number of pseudo terminal pairs are
25 configured.
26 The following ioctl calls apply only to pseudo terminals:
28 TIOCSTOP
30 Stops output to a terminal (e.g. like typing ^S). Takes no
31 parameter.
32 TIOCSTART
34 Restarts output (stopped by TIOCSTOP or by typing ^S). Takes no
35 parameter.
36 TIOCPKT
38 Enable/disable packet mode. Packet mode is enabled by specify‐
39 ing (by reference) a nonzero parameter and disabled by specify‐
40 ing (by reference) a zero parameter. When applied to the master
41 side of a pseudo terminal, each subsequent read from the termi‐
42 nal will return data written on the slave part of the pseudo
43 terminal preceded by a zero byte (symbolically defined as
44 TIOCPKT_DATA), or a single byte reflecting control status infor‐
45 mation. In the latter case, the byte is an inclusive-or of zero
46 or more of the bits:
47 TIOCPKT_FLUSHREAD
49 whenever the read queue for the terminal is flushed.
50 TIOCPKT_FLUSHWRITE
52 whenever the write queue for the terminal is flushed.
53 TIOCPKT_STOP
55 whenever output to the terminal is stopped a la ^S.
56 TIOCPKT_START
58 whenever output to the terminal is restarted.
59 TIOCPKT_DOSTOP
61 whenever t_stopc is ^S and t_startc is ^Q.
62 TIOCPKT_NOSTOP
64 whenever the start and stop characters are not ^S/^Q.
65 While this mode is in use, the presence of control status infor‐
67 mation to be read from the master side may be detected by a
68 select for exceptional conditions.
69 This mode is used by rlogin(1C) and rlogind(8C) to implement a
71 remote-echoed, locally ^S/^Q flow-controlled remote login with
72 proper back-flushing of output; it can be used by other similar
73 programs.
74 TIOCUCNTL
76 Enable/disable a mode that allows a small number of simple user
77 ioctl commands to be passed through the pseudo-terminal, using a
78 protocol similar to that of TIOCPKT. The TIOCUCNTL and TIOCPKT
79 modes are mutually exclusive. This mode is enabled from the
80 master side of a pseudo terminal by specifying (by reference) a
81 nonzero parameter and disabled by specifying (by reference) a
82 zero parameter. Each subsequent read from the master side will
83 return data written on the slave part of the pseudo terminal
84 preceded by a zero byte, or a single byte reflecting a user con‐
85 trol operation on the slave side. A user control command con‐
86 sists of a special ioctl operation with no data; the command is
87 given as UIOCCMD(n), where n is a number in the range 1-255.
88 The operation value n will be received as a single byte on the
89 next read from the master side. The ioctl UIOCCMD(0) is a no-op
90 that may be used to probe for the existence of this facility.
91 As with TIOCPKT mode, command operations may be detected with a
92 select for exceptional conditions.
93 TIOCREMOTE
95 A mode for the master half of a pseudo terminal, independent of
96 TIOCPKT. This mode causes input to the pseudo terminal to be
97 flow controlled and not input edited (regardless of the terminal
98 mode). Each write to the control terminal produces a record
99 boundary for the process reading the terminal. In normal usage,
100 a write of data is like the data typed as a line on the termi‐
101 nal; a write of 0 bytes is like typing an end-of-file character.
102 TIOCREMOTE can be used when doing remote line editing in a win‐
103 dow manager, or whenever flow controlled input is required.
104
106 /dev/pty[p-r][0-9a-f] master pseudo terminals
107 /dev/tty[p-r][0-9a-f] slave pseudo terminals
108
110 None.
1114.2 Berkeley Distribution May 19, 1986 PTY(4)