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46 .TH POSIX_OPENPT 3C "June 18, 2021"
47 .SH NAME
48 posix_openpt \- open a pseudo terminal device
49 .SH SYNOPSIS
50 .nf
51 #include <stdlib.h>
52 #include <fcntl.h>
53
54 \fBint\fR \fBposix_openpt\fR(\fBint\fR \fIoflag\fR);
55 .fi
56
57 .SH DESCRIPTION
58 The \fBposix_openpt()\fR function establishes a connection between a master
59 device for a pseudo-terminal and a file descriptor. The file descriptor is used
60 by other I/O functions that refer to that pseudo-terminal.
61 .sp
62 .LP
63 The file status flags and file access modes of the open file description are
64 set according to the value of \fIoflag\fR.
65 .sp
66 .LP
67 Values for \fIoflag\fR are constructed by a bitwise-inclusive OR of flags from
68 the following list, defined in <\fBfcntl.h\fR>.
69 .sp
70 .ne 2
71 .na
72 \fB\fBO_RDWR\fR\fR
73 .ad
74 .RS 12n
75 Open for reading and writing.
76 .RE
77
78 .sp
79 .ne 2
80 .na
81 \fB\fBO_NOCTTY\fR\fR
82 .ad
83 .RS 12n
84 If set, \fBposix_openpt()\fR does not cause the terminal device to become the
85 controlling terminal for the process.
86 .RE
87
88 .sp
89 .LP
90 The behavior of other values for the \fIoflag\fR argument is unspecified.
91 .SH RETURN VALUES
92 Upon successful completion, the \fBposix_openpt()\fR function opens a master
93 pseudo-terminal device and returns a non-negative integer representing the
94 lowest numbered unused file descriptor. Otherwise, -1 is returned and
95 \fBerrno\fR is set to indicate the error.
96 .SH ERRORS
97 The \fBposix_openpt()\fR function will fail if:
98 .sp
99 .ne 2
100 .na
101 \fB\fBEMFILE\fR\fR
102 .ad
103 .RS 10n
104 {\fBOPEN_MAX\fR} file descriptors are currently open in the calling process.
105 .RE
106
107 .sp
108 .ne 2
109 .na
110 \fB\fBENFILE\fR\fR
111 .ad
112 .RS 10n
113 The maximum allowable number of files is currently open in the system.
114 .RE
115
116 .sp
117 .LP
118 The \fBposix_openpt()\fR function may fail if:
119 .sp
120 .ne 2
121 .na
122 \fB\fBEINVAL\fR\fR
123 .ad
124 .RS 10n
125 The value of \fIoflag\fR is not valid.
126 .RE
127
128 .sp
129 .ne 2
130 .na
131 \fB\fBEAGAIN\fR\fR
132 .ad
133 .RS 10n
134 Out of pseudo-terminal resources.
135 .RE
136
137 .sp
138 .ne 2
139 .na
140 \fB\fBENOSR\fR\fR
141 .ad
142 .RS 10n
143 Out of STREAMS resources.
144 .RE
145
146 .SH EXAMPLES
147 \fBExample 1 \fROpen a pseudo-terminal.
148 .sp
149 .LP
150 The following example opens a pseudo-terminal and returns the name of the slave
151 device and a file descriptor.
152
153 .sp
154 .in +2
155 .nf
156 #include <fcntl.h>
157 #include <stdio.h>
158
159 int masterfd, slavefd;
160 char *slavedevice;
161
162 masterfd = posix_openpt(O_RDWR|O_NOCTTY);
163
164 if (masterfd == -1
165 || grantpt (masterfd) == -1
166 || unlockpt (masterfd) == -1
167 || (slavedevice = ptsname (masterfd)) == NULL)
168 return -1;
169
170 printf("slave device is: %s\en", slavedevice);
171
172 slavefd = open(slave, O_RDWR|O_NOCTTY);
173 if (slavefd < 0)
174 return -1;
175 .fi
176 .in -2
177
178 .SH USAGE
179 This function provides a method for portably obtaining a file descriptor of a
180 master terminal device for a pseudo-terminal. The \fBgrantpt\fR(3C) and
181 \fBptsname\fR(3C) functions can be used to manipulate mode and ownership
182 permissions and to obtain the name of the slave device, respectively.
183 .SH ATTRIBUTES
184 See \fBattributes\fR(5) for descriptions of the following attributes:
185 .sp
186
187 .sp
188 .TS
189 box;
190 c | c
191 l | l .
192 ATTRIBUTE TYPE ATTRIBUTE VALUE
193 _
194 Interface Stability Standard
195 _
196 MT-Level MT-Safe
197 .TE
198
199 .SH SEE ALSO
200 \fBopen\fR(2), \fBgrantpt\fR(3C), \fBptsname\fR(3C), \fBunlockpt\fR(3C),
201 \fBattributes\fR(5), \fBstandards\fR(5)