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7 .TH PTS 7D "Feb 29, 2020"
8 .SH NAME
9 pts \- STREAMS pseudo-tty slave driver
10 .SH DESCRIPTION
11 .sp
12 .LP
13 The pseudo-tty subsystem simulates a terminal connection, where the master side
14 represents the terminal and the slave represents the user process's special
15 device end point. In order to use the pseudo-tty subsystem, a node for the
16 master side driver \fB/dev/ptmx\fR and N nodes for the slave driver (N is
17 determined at installation time) must be installed. The names of the slave
18 devices are \fB/dev/pts/M\fR where \fBM\fR has the values 0 through N-1. When
19 the master device is opened, the corresponding slave device is automatically
20 locked out. No user may open that slave device until its permissions are
21 adjusted and the device unlocked by calling functions \fBgrantpt\fR(3C) and
22 \fBunlockpt\fR(3C). The user can then invoke the open system call with the name
23 that is returned by the \fBptsname\fR(3C) function. See the example below.
24 .sp
25 .LP
26 Only one open is allowed on a master device. Multiple opens are allowed on the
27 slave device. After both the master and slave have been opened, the user has
28 two file descriptors which are end points of a full duplex connection composed
29 of two streams automatically connected at the master and slave drivers. The
30 user may then push modules onto either side of the stream pair. Unless
31 compiled in strict XPG4v2 mode (see below), the consumer needs to push the
32 \fBptem\fR(7M) and \fBldterm\fR(7M) modules onto the slave side of the
33 pseudo-terminal subsystem to get terminal semantics.
34 .sp
35 .LP
36 The master and slave drivers pass all messages to their adjacent queues. Only
37 the \fBM_FLUSH\fR needs some processing. Because the read queue of one side is
38 connected to the write queue of the other, the \fBFLUSHR\fR flag is changed to
39 the \fBFLUSHW\fR flag and vice versa. When the master device is closed an
40 \fBM_HANGUP\fR message is sent to the slave device which will render the device
41 unusable. The process on the slave side gets the errno \fBEIO\fR when
42 attempting to write on that stream but it will be able to read any data
43 remaining on the stream head read queue. When all the data has been read, read
44 returns 0 indicating that the stream can no longer be used. On the last close
45 of the slave device, a 0-length message is sent to the master device. When the
46 application on the master side issues a \fBread()\fR or \fBgetmsg()\fR and 0 is
47 returned, the user of the master device decides whether to issue a
48 \fBclose()\fR that dismantles the pseudo-terminal subsystem. If the master
49 device is not closed, the pseudo-tty subsystem will be available to another
50 user to open the slave device. Since 0-length messages are used to indicate
51 that the process on the slave side has closed and should be interpreted that
52 way by the process on the master side, applications on the slave side should
53 not write 0-length messages. Unless the application is compiled in strict
54 XPG4v2 mode (see below) then any 0-length messages written on the slave side
55 will be discarded by the \fBptem\fR module.
56 .sp
57 .LP
58 The standard STREAMS system calls can access the pseudo-tty devices. The slave
59 devices support the \fBO_NDELAY\fR and \fBO_NONBLOCK\fR flags.
60 .SH STRICT XPG4v2 MODE
61 .sp
62 XPG4v2 requires that open of a slave pseudo terminal device provides the
63 process with an interface that is identical to the terminal interface (without
64 having to explicitly push any modules to achieve this). It also requires that
65 0-length messages written on the slave side will be propagated to the master.
66 .sp
67 Experience has shown, however, that most software does not expect slave pty
68 devices to operate in this manner and therefore this XPG4v2-compliant
69 behaviour is disabled in illumos by default.
70 .sp
71 To enable it for an application, the \fB_XPG4_2\fR and \fB_STRICT_SYMBOLS\fR
72 macros must be set during compilation and the application must be linked with
73 \fBvalues-xpg4.o\fR or \fBvalues-xp6.o\fR.
74 .SH EXAMPLES
75 .sp
76 .in +2
77 .nf
78 int fdm fds;
79 char *slavename;
80 extern char *ptsname();
81
82 fdm = open("/dev/ptmx", O_RDWR); /* open master */
83 grantpt(fdm); /* change permission of slave */
84 unlockpt(fdm); /* unlock slave */
85 slavename = ptsname(fdm); /* get name of slave */
86 fds = open(slavename, O_RDWR); /* open slave */
87 ioctl(fds, I_PUSH, "ptem"); /* push ptem */
88 ioctl(fds, I_PUSH, "ldterm"); /* push ldterm*/
89 .fi
90 .in -2
91
92 .SH FILES
93 .sp
94 .ne 2
95 .na
96 \fB\fB/dev/ptmx\fR\fR
97 .ad
98 .RS 14n
99 master clone device
100 .RE
101
102 .sp
103 .ne 2
104 .na
105 \fB\fB/dev/pts/M\fR\fR
106 .ad
107 .RS 14n
108 slave devices (M = 0 -> N-1)
109 .RE
110
111 .SH SEE ALSO
112 .sp
113 .LP
114 \fBgrantpt\fR(3C), \fBptsname\fR(3C), \fBunlockpt\fR(3C), \fBldterm\fR(7M),
115 \fBptm\fR(7D), \fBptem\fR(7M), \fBstandards\fR(5)
116 .sp
117 .LP
118 \fISTREAMS Programming Guide\fR