1GETSOCKOPT(P) POSIX Programmer's Manual GETSOCKOPT(P)
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6 getsockopt - get the socket options
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9 #include <sys/socket.h>
10 int getsockopt(int socket, int level, int option_name,
12 void *restrict option_value, socklen_t *restrict option_len);
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16 The getsockopt() function manipulates options associated with a socket.
17 The getsockopt() function shall retrieve the value for the option spec‐
19 ified by the option_name argument for the socket specified by the
20 socket argument. If the size of the option value is greater than
21 option_len, the value stored in the object pointed to by the
22 option_value argument shall be silently truncated. Otherwise, the
23 object pointed to by the option_len argument shall be modified to indi‐
24 cate the actual length of the value.
25 The level argument specifies the protocol level at which the option
27 resides. To retrieve options at the socket level, specify the level
28 argument as SOL_SOCKET. To retrieve options at other levels, supply the
29 appropriate level identifier for the protocol controlling the option.
30 For example, to indicate that an option is interpreted by the TCP
31 (Transmission Control Protocol), set level to IPPROTO_TCP as defined in
32 the <netinet/in.h> header.
33 The socket in use may require the process to have appropriate privi‐
35 leges to use the getsockopt() function.
36 The option_name argument specifies a single option to be retrieved. It
38 can be one of the following values defined in <sys/socket.h>:
39 SO_DEBUG
41 Reports whether debugging information is being recorded. This
42 option shall store an int value. This is a Boolean option.
43 SO_ACCEPTCONN
45 Reports whether socket listening is enabled. This option shall
46 store an int value. This is a Boolean option.
47 SO_BROADCAST
49 Reports whether transmission of broadcast messages is supported,
50 if this is supported by the protocol. This option shall store an
51 int value. This is a Boolean option.
52 SO_REUSEADDR
54 Reports whether the rules used in validating addresses supplied
55 to bind() should allow reuse of local addresses, if this is sup‐
56 ported by the protocol. This option shall store an int value.
57 This is a Boolean option.
58 SO_KEEPALIVE
60 Reports whether connections are kept active with periodic trans‐
61 mission of messages, if this is supported by the protocol.
62 If the connected socket fails to respond to these messages, the connec‐
64 tion shall be broken and threads writing to that socket shall be noti‐
65 fied with a SIGPIPE signal. This option shall store an int value. This
66 is a Boolean option.
67 SO_LINGER
69 Reports whether the socket lingers on close() if data is
70 present. If SO_LINGER is set, the system blocks the process
71 during close() until it can transmit the data or until the end
72 of the interval indicated by the l_linger member, whichever
73 comes first. If SO_LINGER is not specified, and close() is
74 issued, the system handles the call in a way that allows the
75 process to continue as quickly as possible. This option shall
76 store a linger structure.
77 SO_OOBINLINE
79 Reports whether the socket leaves received out-of-band data
80 (data marked urgent) inline. This option shall store an int
81 value. This is a Boolean option.
82 SO_SNDBUF
84 Reports send buffer size information. This option shall store an
85 int value.
86 SO_RCVBUF
88 Reports receive buffer size information. This option shall store
89 an int value.
90 SO_ERROR
92 Reports information about error status and clears it. This
93 option shall store an int value.
94 SO_TYPE
96 Reports the socket type. This option shall store an int value.
97 Socket types are described in Socket Types .
98 SO_DONTROUTE
100 Reports whether outgoing messages bypass the standard routing
101 facilities. The destination shall be on a directly-connected
102 network, and messages are directed to the appropriate network
103 interface according to the destination address. The effect, if
104 any, of this option depends on what protocol is in use. This
105 option shall store an int value. This is a Boolean option.
106 SO_RCVLOWAT
108 Reports the minimum number of bytes to process for socket input
109 operations. The default value for SO_RCVLOWAT is 1. If
110 SO_RCVLOWAT is set to a larger value, blocking receive calls
111 normally wait until they have received the smaller of the low
112 water mark value or the requested amount. (They may return less
113 than the low water mark if an error occurs, a signal is caught,
114 or the type of data next in the receive queue is different from
115 that returned; for example, out-of-band data.) This option shall
116 store an int value. Note that not all implementations allow this
117 option to be retrieved.
118 SO_RCVTIMEO
120 Reports the timeout value for input operations. This option
121 shall store a timeval structure with the number of seconds and
122 microseconds specifying the limit on how long to wait for an
123 input operation to complete. If a receive operation has blocked
124 for this much time without receiving additional data, it shall
125 return with a partial count or errno set to [EAGAIN] or [EWOULD‐
126 BLOCK] if no data was received. The default for this option is
127 zero, which indicates that a receive operation shall not time
128 out. Note that not all implementations allow this option to be
129 retrieved.
130 SO_SNDLOWAT
132 Reports the minimum number of bytes to process for socket output
133 operations. Non-blocking output operations shall process no
134 data if flow control does not allow the smaller of the send low
135 water mark value or the entire request to be processed. This
136 option shall store an int value. Note that not all implementa‐
137 tions allow this option to be retrieved.
138 SO_SNDTIMEO
140 Reports the timeout value specifying the amount of time that an
141 output function blocks because flow control prevents data from
142 being sent. If a send operation has blocked for this time, it
143 shall return with a partial count or with errno set to [EAGAIN]
144 or [EWOULDBLOCK] if no data was sent. The default for this
145 option is zero, which indicates that a send operation shall not
146 time out. The option shall store a timeval structure. Note that
147 not all implementations allow this option to be retrieved.
148 For Boolean options, a zero value indicates that the option is disabled
151 and a non-zero value indicates that the option is enabled.
152
154 Upon successful completion, getsockopt() shall return 0; otherwise, -1
155 shall be returned and errno set to indicate the error.
156
158 The getsockopt() function shall fail if:
159 EBADF The socket argument is not a valid file descriptor.
161 EINVAL The specified option is invalid at the specified socket level.
163 ENOPROTOOPT
165 The option is not supported by the protocol.
167 ENOTSOCK
169 The socket argument does not refer to a socket.
170 The getsockopt() function may fail if:
173 EACCES The calling process does not have the appropriate privileges.
175 EINVAL The socket has been shut down.
177 ENOBUFS
179 Insufficient resources are available in the system to complete
180 the function.
181 The following sections are informative.
184
186 None.
187
189 None.
190
192 None.
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195 None.
196
198 bind() , close() , endprotoent() , setsockopt() , socket() , the Base
199 Definitions volume of IEEE Std 1003.1-2001, <sys/socket.h>,
200 <netinet/in.h>
201
203 Portions of this text are reprinted and reproduced in electronic form
204 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
205 -- Portable Operating System Interface (POSIX), The Open Group Base
206 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
207 Electrical and Electronics Engineers, Inc and The Open Group. In the
208 event of any discrepancy between this version and the original IEEE and
209 The Open Group Standard, the original IEEE and The Open Group Standard
210 is the referee document. The original Standard can be obtained online
211 at http://www.opengroup.org/unix/online.html .
212IEEE/The Open Group 2003 GETSOCKOPT(P)