1SETSOCKOPT(P) POSIX Programmer's Manual SETSOCKOPT(P)
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6 setsockopt - set the socket options
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9 #include <sys/socket.h>
10 int setsockopt(int socket, int level, int option_name,
12 const void *option_value, socklen_t option_len);
13
16 The setsockopt() function shall set the option specified by the
17 option_name argument, at the protocol level specified by the level
18 argument, to the value pointed to by the option_value argument for the
19 socket associated with the file descriptor specified by the socket
20 argument.
21 The level argument specifies the protocol level at which the option
23 resides. To set options at the socket level, specify the level argument
24 as SOL_SOCKET. To set options at other levels, supply the appropriate
25 level identifier for the protocol controlling the option. For example,
26 to indicate that an option is interpreted by the TCP (Transport Control
27 Protocol), set level to IPPROTO_TCP as defined in the <netinet/in.h>
28 header.
29 The option_name argument specifies a single option to set. The
31 option_name argument and any specified options are passed uninterpreted
32 to the appropriate protocol module for interpretations. The
33 <sys/socket.h> header defines the socket-level options. The options
34 are as follows:
35 SO_DEBUG
37 Turns on recording of debugging information. This option enables
38 or disables debugging in the underlying protocol modules. This
39 option takes an int value. This is a Boolean option.
40 SO_BROADCAST
42 Permits sending of broadcast messages, if this is supported by
43 the protocol. This option takes an int value. This is a Boolean
44 option.
45 SO_REUSEADDR
47 Specifies that the rules used in validating addresses supplied
48 to bind() should allow reuse of local addresses, if this is sup‐
49 ported by the protocol. This option takes an int value. This is
50 a Boolean option.
51 SO_KEEPALIVE
53 Keeps connections active by enabling the periodic transmission
54 of messages, if this is supported by the protocol. This option
55 takes an int value.
56 If the connected socket fails to respond to these messages, the connec‐
58 tion is broken and threads writing to that socket are notified with a
59 SIGPIPE signal. This is a Boolean option.
60 SO_LINGER
62 Lingers on a close() if data is present. This option controls
63 the action taken when unsent messages queue on a socket and
64 close() is performed. If SO_LINGER is set, the system shall
65 block the process during close() until it can transmit the data
66 or until the time expires. If SO_LINGER is not specified, and
67 close() is issued, the system handles the call in a way that
68 allows the process to continue as quickly as possible. This
69 option takes a linger structure, as defined in the
70 <sys/socket.h> header, to specify the state of the option and
71 linger interval.
72 SO_OOBINLINE
74 Leaves received out-of-band data (data marked urgent) inline.
75 This option takes an int value. This is a Boolean option.
76 SO_SNDBUF
78 Sets send buffer size. This option takes an int value.
79 SO_RCVBUF
81 Sets receive buffer size. This option takes an int value.
82 SO_DONTROUTE
84 Requests that outgoing messages bypass the standard routing
85 facilities. The destination shall be on a directly-connected
86 network, and messages are directed to the appropriate network
87 interface according to the destination address. The effect, if
88 any, of this option depends on what protocol is in use. This
89 option takes an int value. This is a Boolean option.
90 SO_RCVLOWAT
92 Sets the minimum number of bytes to process for socket input
93 operations. The default value for SO_RCVLOWAT is 1. If
94 SO_RCVLOWAT is set to a larger value, blocking receive calls
95 normally wait until they have received the smaller of the low
96 water mark value or the requested amount. (They may return less
97 than the low water mark if an error occurs, a signal is caught,
98 or the type of data next in the receive queue is different from
99 that returned; for example, out-of-band data.) This option takes
100 an int value. Note that not all implementations allow this
101 option to be set.
102 SO_RCVTIMEO
104 Sets the timeout value that specifies the maximum amount of time
105 an input function waits until it completes. It accepts a timeval
106 structure with the number of seconds and microseconds specifying
107 the limit on how long to wait for an input operation to com‐
108 plete. If a receive operation has blocked for this much time
109 without receiving additional data, it shall return with a par‐
110 tial count or errno set to [EAGAIN] or [EWOULDBLOCK] if no data
111 is received. The default for this option is zero, which indi‐
112 cates that a receive operation shall not time out. This option
113 takes a timeval structure. Note that not all implementations
114 allow this option to be set.
115 SO_SNDLOWAT
117 Sets the minimum number of bytes to process for socket output
118 operations. Non-blocking output operations shall process no
119 data if flow control does not allow the smaller of the send low
120 water mark value or the entire request to be processed. This
121 option takes an int value. Note that not all implementations
122 allow this option to be set.
123 SO_SNDTIMEO
125 Sets the timeout value specifying the amount of time that an
126 output function blocks because flow control prevents data from
127 being sent. If a send operation has blocked for this time, it
128 shall return with a partial count or with errno set to [EAGAIN]
129 or [EWOULDBLOCK] if no data is sent. The default for this option
130 is zero, which indicates that a send operation shall not time
131 out. This option stores a timeval structure. Note that not all
132 implementations allow this option to be set.
133 For Boolean options, 0 indicates that the option is disabled and 1
136 indicates that the option is enabled.
137 Options at other protocol levels vary in format and name.
139
141 Upon successful completion, setsockopt() shall return 0. Otherwise, -1
142 shall be returned and errno set to indicate the error.
143
145 The setsockopt() function shall fail if:
146 EBADF The socket argument is not a valid file descriptor.
148 EDOM The send and receive timeout values are too big to fit into the
150 timeout fields in the socket structure.
151 EINVAL The specified option is invalid at the specified socket level or
153 the socket has been shut down.
154 EISCONN
156 The socket is already connected, and a specified option cannot
157 be set while the socket is connected.
158 ENOPROTOOPT
160 The option is not supported by the protocol.
162 ENOTSOCK
164 The socket argument does not refer to a socket.
165 The setsockopt() function may fail if:
168 ENOMEM There was insufficient memory available for the operation to
170 complete.
171 ENOBUFS
173 Insufficient resources are available in the system to complete
174 the call.
175 The following sections are informative.
178
180 None.
181
183 The setsockopt() function provides an application program with the
184 means to control socket behavior. An application program can use set‐
185 sockopt() to allocate buffer space, control timeouts, or permit socket
186 data broadcasts. The <sys/socket.h> header defines the socket-level
187 options available to setsockopt().
188 Options may exist at multiple protocol levels. The SO_ options are
190 always present at the uppermost socket level.
191
193 None.
194
196 None.
197
199 Sockets , bind() , endprotoent() , getsockopt() , socket() , the Base
200 Definitions volume of IEEE Std 1003.1-2001, <netinet/in.h>,
201 <sys/socket.h>
202
204 Portions of this text are reprinted and reproduced in electronic form
205 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
206 -- Portable Operating System Interface (POSIX), The Open Group Base
207 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
208 Electrical and Electronics Engineers, Inc and The Open Group. In the
209 event of any discrepancy between this version and the original IEEE and
210 The Open Group Standard, the original IEEE and The Open Group Standard
211 is the referee document. The original Standard can be obtained online
212 at http://www.opengroup.org/unix/online.html .
213IEEE/The Open Group 2003 SETSOCKOPT(P)