1GETSOCKOPT(3P) POSIX Programmer's Manual GETSOCKOPT(3P)
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6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
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12 getsockopt - get the socket options
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15 #include <sys/socket.h>
16 int getsockopt(int socket, int level, int option_name,
18 void *restrict option_value, socklen_t *restrict option_len);
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22 The getsockopt() function manipulates options associated with a socket.
23 The getsockopt() function shall retrieve the value for the option spec‐
25 ified by the option_name argument for the socket specified by the
26 socket argument. If the size of the option value is greater than
27 option_len, the value stored in the object pointed to by the
28 option_value argument shall be silently truncated. Otherwise, the
29 object pointed to by the option_len argument shall be modified to indi‐
30 cate the actual length of the value.
31 The level argument specifies the protocol level at which the option
33 resides. To retrieve options at the socket level, specify the level
34 argument as SOL_SOCKET. To retrieve options at other levels, supply the
35 appropriate level identifier for the protocol controlling the option.
36 For example, to indicate that an option is interpreted by the TCP
37 (Transmission Control Protocol), set level to IPPROTO_TCP as defined in
38 the <netinet/in.h> header.
39 The socket in use may require the process to have appropriate privi‐
41 leges to use the getsockopt() function.
42 The option_name argument specifies a single option to be retrieved. It
44 can be one of the following values defined in <sys/socket.h>:
45 SO_DEBUG
47 Reports whether debugging information is being recorded. This
48 option shall store an int value. This is a Boolean option.
49 SO_ACCEPTCONN
51 Reports whether socket listening is enabled. This option shall
52 store an int value. This is a Boolean option.
53 SO_BROADCAST
55 Reports whether transmission of broadcast messages is supported,
56 if this is supported by the protocol. This option shall store an
57 int value. This is a Boolean option.
58 SO_REUSEADDR
60 Reports whether the rules used in validating addresses supplied
61 to bind() should allow reuse of local addresses, if this is sup‐
62 ported by the protocol. This option shall store an int value.
63 This is a Boolean option.
64 SO_KEEPALIVE
66 Reports whether connections are kept active with periodic trans‐
67 mission of messages, if this is supported by the protocol.
68 If the connected socket fails to respond to these messages, the connec‐
70 tion shall be broken and threads writing to that socket shall be noti‐
71 fied with a SIGPIPE signal. This option shall store an int value. This
72 is a Boolean option.
73 SO_LINGER
75 Reports whether the socket lingers on close() if data is
76 present. If SO_LINGER is set, the system blocks the process
77 during close() until it can transmit the data or until the end
78 of the interval indicated by the l_linger member, whichever
79 comes first. If SO_LINGER is not specified, and close() is
80 issued, the system handles the call in a way that allows the
81 process to continue as quickly as possible. This option shall
82 store a linger structure.
83 SO_OOBINLINE
85 Reports whether the socket leaves received out-of-band data
86 (data marked urgent) inline. This option shall store an int
87 value. This is a Boolean option.
88 SO_SNDBUF
90 Reports send buffer size information. This option shall store an
91 int value.
92 SO_RCVBUF
94 Reports receive buffer size information. This option shall store
95 an int value.
96 SO_ERROR
98 Reports information about error status and clears it. This
99 option shall store an int value.
100 SO_TYPE
102 Reports the socket type. This option shall store an int value.
103 Socket types are described in Socket Types .
104 SO_DONTROUTE
106 Reports whether outgoing messages bypass the standard routing
107 facilities. The destination shall be on a directly-connected
108 network, and messages are directed to the appropriate network
109 interface according to the destination address. The effect, if
110 any, of this option depends on what protocol is in use. This
111 option shall store an int value. This is a Boolean option.
112 SO_RCVLOWAT
114 Reports the minimum number of bytes to process for socket input
115 operations. The default value for SO_RCVLOWAT is 1. If
116 SO_RCVLOWAT is set to a larger value, blocking receive calls
117 normally wait until they have received the smaller of the low
118 water mark value or the requested amount. (They may return less
119 than the low water mark if an error occurs, a signal is caught,
120 or the type of data next in the receive queue is different from
121 that returned; for example, out-of-band data.) This option shall
122 store an int value. Note that not all implementations allow this
123 option to be retrieved.
124 SO_RCVTIMEO
126 Reports the timeout value for input operations. This option
127 shall store a timeval structure with the number of seconds and
128 microseconds specifying the limit on how long to wait for an
129 input operation to complete. If a receive operation has blocked
130 for this much time without receiving additional data, it shall
131 return with a partial count or errno set to [EAGAIN] or [EWOULD‐
132 BLOCK] if no data was received. The default for this option is
133 zero, which indicates that a receive operation shall not time
134 out. Note that not all implementations allow this option to be
135 retrieved.
136 SO_SNDLOWAT
138 Reports the minimum number of bytes to process for socket output
139 operations. Non-blocking output operations shall process no
140 data if flow control does not allow the smaller of the send low
141 water mark value or the entire request to be processed. This
142 option shall store an int value. Note that not all implementa‐
143 tions allow this option to be retrieved.
144 SO_SNDTIMEO
146 Reports the timeout value specifying the amount of time that an
147 output function blocks because flow control prevents data from
148 being sent. If a send operation has blocked for this time, it
149 shall return with a partial count or with errno set to [EAGAIN]
150 or [EWOULDBLOCK] if no data was sent. The default for this
151 option is zero, which indicates that a send operation shall not
152 time out. The option shall store a timeval structure. Note that
153 not all implementations allow this option to be retrieved.
154 For Boolean options, a zero value indicates that the option is disabled
157 and a non-zero value indicates that the option is enabled.
158
160 Upon successful completion, getsockopt() shall return 0; otherwise, -1
161 shall be returned and errno set to indicate the error.
162
164 The getsockopt() function shall fail if:
165 EBADF The socket argument is not a valid file descriptor.
167 EINVAL The specified option is invalid at the specified socket level.
169 ENOPROTOOPT
171 The option is not supported by the protocol.
173 ENOTSOCK
175 The socket argument does not refer to a socket.
176 The getsockopt() function may fail if:
179 EACCES The calling process does not have the appropriate privileges.
181 EINVAL The socket has been shut down.
183 ENOBUFS
185 Insufficient resources are available in the system to complete
186 the function.
187 The following sections are informative.
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192 None.
193
195 None.
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198 None.
199
201 None.
202
204 bind(), close(), endprotoent(), setsockopt(), socket(), the Base Defi‐
205 nitions volume of IEEE Std 1003.1-2001, <sys/socket.h>, <netinet/in.h>
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208 Portions of this text are reprinted and reproduced in electronic form
209 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
210 -- Portable Operating System Interface (POSIX), The Open Group Base
211 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
212 Electrical and Electronics Engineers, Inc and The Open Group. In the
213 event of any discrepancy between this version and the original IEEE and
214 The Open Group Standard, the original IEEE and The Open Group Standard
215 is the referee document. The original Standard can be obtained online
216 at http://www.opengroup.org/unix/online.html .
217IEEE/The Open Group 2003 GETSOCKOPT(3P)