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34 .\" @(#)getsockopt.2 8.3 (Berkeley) 4/19/94
42 .Nd get and set options on sockets
44 .Fd #include <sys/types.h>
45 .Fd #include <sys/socket.h>
47 .Fn getsockopt "int s" "int level" "int optname" "void *optval" "socklen_t *optlen"
49 .Fn setsockopt "int s" "int level" "int optname" "const void *optval" "socklen_t optlen"
56 associated with a socket. Options may exist at multiple
57 protocol levels; they are always present at the uppermost
61 When manipulating socket options the level at which the
62 option resides and the name of the option must be specified.
63 To manipulate options at the socket level,
67 To manipulate options at any
68 other level the protocol number of the appropriate protocol
69 controlling the option is supplied. For example,
70 to indicate that an option is to be interpreted by the
74 should be set to the protocol number of
83 are used to access option values for
87 they identify a buffer in which the value for the
88 requested option(s) are to be returned. For
91 is a value-result parameter, initially containing the
92 size of the buffer pointed to by
94 and modified on return to indicate the actual size of
95 the value returned. If no option value is
96 to be supplied or returned,
101 and any specified options are passed uninterpreted to the appropriate
102 protocol module for interpretation.
104 .Ao Pa sys/socket.h Ac
105 contains definitions for
106 socket level options, described below.
107 Options at other protocol levels vary in format and
108 name; consult the appropriate entries in
112 Most socket-level options utilize an
118 the parameter should be non-zero to enable a boolean option,
119 or zero if the option is to be disabled.
123 parameter, defined in
124 .Ao Pa sys/socket.h Ac ,
125 which specifies the desired state of the option and the
126 linger interval (see below).
132 parameter, defined in
133 .Ao Pa sys/time.h Ac .
135 The following options are recognized at the socket level.
136 Except as noted, each may be examined with
140 .Bl -column SO_OOBINLINE -offset indent
141 .It Dv SO_DEBUG Ta "enables recording of debugging information"
142 .It Dv SO_REUSEADDR Ta "enables local address reuse"
143 .It Dv SO_REUSEPORT Ta "enables duplicate address and port bindings"
144 .It Dv SO_KEEPALIVE Ta "enables keep connections alive"
145 .It Dv SO_DONTROUTE Ta "enables routing bypass for outgoing messages"
146 .It Dv SO_LINGER Ta "linger on close if data present"
147 .It Dv SO_BROADCAST Ta "enables permission to transmit broadcast messages"
148 .It Dv SO_OOBINLINE Ta "enables reception of out-of-band data in band"
149 .It Dv SO_SNDBUF Ta "set buffer size for output"
150 .It Dv SO_RCVBUF Ta "set buffer size for input"
151 .It Dv SO_SNDLOWAT Ta "set minimum count for output"
152 .It Dv SO_RCVLOWAT Ta "set minimum count for input"
153 .It Dv SO_SNDTIMEO Ta "set timeout value for output"
154 .It Dv SO_RCVTIMEO Ta "set timeout value for input"
155 .It Dv SO_TYPE Ta "get the type of the socket (get only)"
156 .It Dv SO_ERROR Ta "get and clear error on the socket (get only)"
157 .It Dv SO_NOSIGPIPE Ta "do not generate SIGPIPE, instead return EPIPE"
161 enables debugging in the underlying protocol modules.
163 indicates that the rules used in validating addresses supplied
166 call should allow reuse of local addresses.
168 allows completely duplicate bindings by multiple processes
171 before binding the port.
172 This option permits multiple instances of a program to each
173 receive UDP/IP multicast or broadcast datagrams destined for the bound port.
176 periodic transmission of messages on a connected socket. Should the
177 connected party fail to respond to these messages, the connection is
178 considered broken and processes using the socket are notified via a
180 signal when attempting to send data.
182 indicates that outgoing messages should
183 bypass the standard routing facilities. Instead, messages are directed
184 to the appropriate network interface according to the network portion
185 of the destination address.
188 controls the action taken when unsent messages
189 are queued on socket and a
192 If the socket promises reliable delivery of data and
193 .Dv SO_LINGER is set,
194 the system will block the process on the
196 attempt until it is able to transmit the data or until it decides it
197 is unable to deliver the information (a timeout period, termed the
198 linger interval, is specified in the
207 is issued, the system will process the close in a manner that allows
208 the process to continue as quickly as possible.
212 requests permission to send broadcast datagrams
214 Broadcast was a privileged operation in earlier versions of the system.
215 With protocols that support out-of-band data, the
218 requests that out-of-band data be placed in the normal data input queue
219 as received; it will then be accessible with
226 Some protocols always behave as if this option is set.
230 are options to adjust the normal
231 buffer sizes allocated for output and input buffers, respectively.
232 The buffer size may be increased for high-volume connections,
233 or may be decreased to limit the possible backlog of incoming data.
234 The system places an absolute limit on these values.
237 is an option to set the minimum count for output operations.
238 Most output operations process all of the data supplied
239 by the call, delivering data to the protocol for transmission
240 and blocking as necessary for flow control.
241 Nonblocking output operations will process as much data as permitted
242 subject to flow control without blocking, but will process no data
243 if flow control does not allow the smaller of the low water mark value
244 or the entire request to be processed.
247 operation testing the ability to write to a socket will return true
248 only if the low water mark amount could be processed.
249 The default value for
251 is set to a convenient size for network efficiency, often 1024.
253 is an option to set the minimum count for input operations.
254 In general, receive calls will block until any (non-zero) amount of data
255 is received, then return with the smaller of the amount available or the amount
257 The default value for
262 is set to a larger value, blocking receive calls normally
263 wait until they have received the smaller of the low water mark value
264 or the requested amount.
265 Receive calls may still return less than the low water mark if an error
266 occurs, a signal is caught, or the type of data next in the receive queue
267 is different than that returned.
270 is an option to set a timeout value for output operations.
273 parameter with the number of seconds and microseconds
274 used to limit waits for output operations to complete.
275 If a send operation has blocked for this much time,
276 it returns with a partial count
279 if no data were sent.
280 In the current implementation, this timer is restarted each time additional
281 data are delivered to the protocol,
282 implying that the limit applies to output portions ranging in size
283 from the low water mark to the high water mark for output.
285 is an option to set a timeout value for input operations.
288 parameter with the number of seconds and microseconds
289 used to limit waits for input operations to complete.
290 In the current implementation, this timer is restarted each time additional
291 data are received by the protocol,
292 and thus the limit is in effect an inactivity timer.
293 If a receive operation has been blocked for this much time without
294 receiving additional data, it returns with a short count
297 if no data were received. The struct timeval parameter must represent a
298 positive time interval otherwise
300 returns with the error
303 .Dv SO_NOSIGPIPE is an option that prevents SIGPIPE from being raised
304 when a write fails on a socket to which there is no reader;
305 instead the write to the socket returns with the error
307 when there is no reader.
313 are options used only with
316 returns the type of the socket, such as
318 it is useful for servers that inherit sockets on startup.
320 returns any pending error on the socket and clears
322 It may be used to check for asynchronous errors on connected
323 datagram sockets or for other asynchronous errors.
325 A 0 is returned if the call succeeds, -1 if it fails.
327 The call succeeds unless:
332 is not a valid descriptor.
336 is a file, not a socket.
337 .It Bq Er ENOPROTOOPT
338 The option is unknown at the level indicated.
340 The address pointed to by
342 is not in a valid part of the process address space.
345 this error may also be returned if
347 is not in a valid part of the process address space.
349 The argument value is out of bounds.
357 Several of the socket options should be handled at lower levels of the system.
361 system call appeared in
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