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32 .\" @(#)pty.4 8.2 (Berkeley) 11/30/93
40 .Nd pseudo terminal driver
46 driver provides support for a device-pair termed a
48 A pseudo terminal is a pair of character devices, a
53 The slave device provides to a process an interface identical
56 However, whereas all other devices which provide the
57 interface described in
59 have a hardware device of some sort behind them, the slave
60 device has, instead, another process manipulating
61 it through the master half of the pseudo terminal.
62 That is, anything written on the master device is
63 given to the slave device as input and anything written
64 on the slave device is presented as input on the master
69 calls apply only to pseudo terminals:
70 .Bl -tag -width TIOCREMOTE
72 Stops output to a terminal (e.g.\& like typing
77 Restarts output (stopped by
86 Packet mode is enabled by specifying (by reference)
87 a nonzero parameter and disabled by specifying (by reference)
89 When applied to the master side of a pseudo terminal, each subsequent
91 from the terminal will return data written on the slave part of
92 the pseudo terminal preceded by a zero byte (symbolically
95 or a single byte reflecting control
97 In the latter case, the byte is an inclusive-or
98 of zero or more of the bits:
99 .Bl -tag -width TIOCPKT_FLUSHWRITE
100 .It Dv TIOCPKT_FLUSHREAD
101 whenever the read queue for the terminal is flushed.
102 .It Dv TIOCPKT_FLUSHWRITE
103 whenever the write queue for the terminal is flushed.
105 whenever output to the terminal is stopped a la
108 whenever output to the terminal is restarted.
109 .It Dv TIOCPKT_DOSTOP
118 .It Dv TIOCPKT_NOSTOP
119 whenever the start and stop characters are not
123 While this mode is in use, the presence of control status information
124 to be read from the master side may be detected by a
126 for exceptional conditions.
132 to implement a remote-echoed, locally
135 remote login with proper back-flushing of output; it can be
136 used by other similar programs.
138 Enable/disable a mode that allows a small number of simple user
140 commands to be passed through the pseudo-terminal,
141 using a protocol similar to that of
147 modes are mutually exclusive.
148 This mode is enabled from the master side of a pseudo terminal
149 by specifying (by reference)
150 a nonzero parameter and disabled by specifying (by reference)
154 from the master side will return data written on the slave part of
155 the pseudo terminal preceded by a zero byte,
156 or a single byte reflecting a user control operation on the slave side.
157 A user control command consists of a special
159 operation with no data; the command is given as
163 is a number in the range 1-255.
166 will be received as a single byte on the next
168 from the master side.
172 is a no-op that may be used to probe for
173 the existence of this facility.
176 mode, command operations may be detected with a
178 for exceptional conditions.
181 There is currently two
183 systems available: the original
186 SysVR4 pts-like implementation.
187 It is possible to switch between the two implementations by setting the
190 Setting it to 0 will use the
192 to non-zero the pts implementation.
194 It is possible to set the maximum number of ptys
195 which can be allocated at the same time with the
199 It is not recommended to use more than 1000 pseudo-terminals, as all software
202 will not be able to handle pseudo-terminals with number superior to 999.
204 The pts implementation also supports the
207 call, which takes a pointer to an
209 as a parameter and provides the
212 The files used by the
214 pseudo terminals implementation are:
216 .Bl -tag -width ".Pa /dev/tty[p-sP-S][0-9a-v]" -compact
217 .It Pa /dev/pty[p-sP-S][0-9a-v]
218 master pseudo terminals
219 .It Pa /dev/tty[p-sP-S][0-9a-v]
220 slave pseudo terminals
223 The files used by the pts implementation are:
225 .Bl -tag -width ".Pa /dev/pts/[num]" -compact
227 control device, returns a file descriptor to a new master pseudo terminal
230 master pseudo terminals
231 .It Pa /dev/pts/[num]
232 slave pseudo terminals