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47 .Dd February 5, 2022
48 .Dt POSIX_OPENPT 3C
49 .Os
50 .Sh NAME
51 .Nm posix_openpt
52 .Nd open a pseudo-terminal manager device
53 .Sh SYNOPSIS
54 .In stdlib.h
55 .In fcntl.h
56 .Ft int
57 .Fo posix_openpt
58 .Fa "int oflag"
59 .Fc
60 .Sh DESCRIPTION
61 The
62 .Fn posix_openpt
63 function establishes a connection between a manager device for a
64 pseudo-terminal and a file descriptor.
65 The file descriptor is used by other I/O functions that refer to that
66 pseudo-terminal.
67 .Pp
68 The file status flags and file access modes of the open file description are
69 set according to the value of
70 .Fa oflag .
71 .Pp
72 Values for
73 .Fa oflag
74 are constructed by a bitwise-inclusive OR of flags from
75 the following list, defined in
76 .Xr fcntl.h 3HEAD :
77 .Bl -tag -width Ds
78 .It Dv O_RDWR
79 Open for reading and writing.
80 .It Dv O_NOCTTY
81 If set,
82 .Fn posix_openpt
83 does not cause the terminal device to become the controlling terminal for the
84 process.
85 .El
86 .Pp
87 The behavior of other values for the
88 .Fa oflag
89 argument is unspecified.
90 .Sh RETURN VALUES
91 The
92 .Fn posix_getopt
93 function opens a manager pseudo-terminal device and, if successful, returns a
94 non-negative integer representing the lowest numbered unused file descriptor ;
95 otherwise, the value
96 .Sy -1
97 is returned and the global variable
98 .Va errno
99 is set to indicate the error.
100 .Sh EXAMPLES
101 .Sy Example 1
102 Open a pseudo-terminal.
103 .Pp
104 The following example opens a pseudo-terminal and returns the name of the
105 subsidiary device and a file descriptor.
106 .Bd -literal -offset Ds
107 #include <fcntl.h>
108 #include <stdio.h>
109 #include <err.h>
110
111 int managerfd, subsidiaryfd;
112 char *subsidiarydevice;
113
114 if ((managerfd = posix_openpt(O_RDWR|O_NOCTTY)) < 0) {
115 err(1, "opening pseudo-terminal manager");
116 }
117
118 if (grantpt(managerfd) != 0 ||
119 unlockpt(managerfd) != 0 ||
120 (subsidiarydevice = ptsname(managerfd)) == NULL) {
121 (void) close(managerfd);
122 err(1, "locating pseudo-terminal subsidiary");
123 }
124
125 printf("subsidiary device is: %s\en", subsidiarydevice);
126
127 if ((subsidiaryfd = open(subsidiary, O_RDWR|O_NOCTTY)) < 0) {
128 err(1, "opening pseudo-terminal subsidiary");
129 }
130 .Ed
131 .Sh ERRORS
132 The
133 .Fn posix_openpt
134 function will fail if:
135 .Bl -tag -width Er
136 .It Er EMFILE
137 .Brq Dv OPEN_MAX
138 file descriptors are currently open in the calling process.
139 .It Er ENFILE
140 The maximum allowable number of files is currently open in the system.
141 .El
142 .Pp
143 The
144 .Fn posix_openpt
145 function may fail if:
146 .Bl -tag -width Er
147 .It Er EINVAL
148 The value of
149 .Fa oflag
150 is not valid.
151 .It Er EAGAIN
152 The system has run out of pseudo-terminal resources.
153 .It Er ENOSR
154 The system has run out of STREAMS resources.
155 .El
156 .Sh USAGE
157 This function provides a portable method for obtaining the file descriptor of a
158 manager terminal device for a pseudo-terminal, as opposed to using
159 .Xr open 2
160 on the
161 .Xr ptm 7D
162 device which is system-specific.
163 .Pp
164 The
165 .Xr grantpt 3C
166 function can be used to manipulate the mode and ownership permissions
167 of the subsidiary device.
168 The
169 .Xr ptsname 3C
170 function can be used to obtain the name of the subsidiary device.
171 .Sh INTERFACE STABILITY
172 .Sy Committed
173 .Sh MT LEVEL
174 .Sy MT-Safe
175 .Sh SEE ALSO
176 .Xr open 2 ,
177 .Xr grantpt 3C ,
178 .Xr ptsname 3C ,
179 .Xr unlockpt 3C ,
180 .Xr attributes 5 ,
181 .Xr standards 5 ,
182 .Xr ptm 7D ,
183 .Xr pts 7D