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28 .\" @(#)getsockopt.2 8.4 (Berkeley) 5/2/95
29 .\" $FreeBSD: src/lib/libc/sys/getsockopt.2,v 1.12.2.11 2002/01/09 17:44:15 yar Exp $
37 .Nd get and set options on sockets
44 .Fn getsockopt "int s" "int level" "int optname" "void *optval" "socklen_t *optlen"
46 .Fn setsockopt "int s" "int level" "int optname" "const void *optval" "socklen_t optlen"
53 associated with a socket. Options may exist at multiple
54 protocol levels; they are always present at the uppermost
58 When manipulating socket options the level at which the
59 option resides and the name of the option must be specified.
60 To manipulate options at the socket level,
64 To manipulate options at any
65 other level the protocol number of the appropriate protocol
66 controlling the option is supplied. For example,
67 to indicate that an option is to be interpreted by the
71 should be set to the protocol number of
80 are used to access option values for
84 they identify a buffer in which the value for the
85 requested option(s) are to be returned. For
88 is a value-result parameter, initially containing the
89 size of the buffer pointed to by
91 and modified on return to indicate the actual size of
92 the value returned. If no option value is
93 to be supplied or returned,
98 and any specified options are passed uninterpreted to the appropriate
99 protocol module for interpretation.
102 contains definitions for
103 socket level options, described below.
104 Options at other protocol levels vary in format and
105 name; consult the appropriate entries in
109 Most socket-level options utilize an
115 the parameter should be non-zero to enable a boolean option,
116 or zero if the option is to be disabled.
120 parameter, defined in
122 which specifies the desired state of the option and the
123 linger interval (see below).
129 parameter, defined in
132 The following options are recognized at the socket level.
133 Except as noted, each may be examined with
137 .Bl -column SO_ACCEPTFILTER -offset indent
138 .It Dv SO_DEBUG Ta "enables recording of debugging information"
139 .It Dv SO_REUSEADDR Ta "enables local address reuse"
140 .It Dv SO_REUSEPORT Ta "enables duplicate address and port bindings"
141 .It Dv SO_KEEPALIVE Ta "enables keep connections alive"
142 .It Dv SO_DONTROUTE Ta "enables routing bypass for outgoing messages"
143 .It Dv SO_LINGER Ta "linger on close if data present"
144 .It Dv SO_BROADCAST Ta "enables permission to transmit broadcast messages"
145 .It Dv SO_OOBINLINE Ta "enables reception of out-of-band data in band"
146 .It Dv SO_SNDBUF Ta "set buffer size for output"
147 .It Dv SO_RCVBUF Ta "set buffer size for input"
148 .It Dv SO_SNDLOWAT Ta "set minimum count for output"
149 .It Dv SO_RCVLOWAT Ta "set minimum count for input"
150 .It Dv SO_SNDTIMEO Ta "set timeout value for output"
151 .It Dv SO_RCVTIMEO Ta "set timeout value for input"
152 .It Dv SO_ACCEPTFILTER Ta "set accept filter on listening socket"
153 .It Dv SO_TYPE Ta "get the type of the socket (get only)"
154 .It Dv SO_ERROR Ta "get and clear error on the socket (get only)"
155 .It Dv SO_RERROR Ta "enables receive error reporting"
159 enables debugging in the underlying protocol modules.
161 indicates that the rules used in validating addresses supplied
164 call should allow reuse of local addresses.
166 allows completely duplicate bindings by multiple processes
169 before binding the port.
170 This option permits multiple instances of a program to each
171 receive UDP/IP multicast or broadcast datagrams destined for the bound port.
174 periodic transmission of messages on a connected socket. Should the
175 connected party fail to respond to these messages, the connection is
176 considered broken and processes using the socket are notified via a
178 signal when attempting to send data.
180 indicates that outgoing messages should
181 bypass the standard routing facilities. Instead, messages are directed
182 to the appropriate network interface according to the network portion
183 of the destination address.
185 indicates that receive buffer overflows should be handled as errors.
186 Historically receive buffer overflows have been ignored and programs
187 could not tell if they missed messages or messages had been truncated
188 because of overflows.
189 Since programs historically do not expect to get receive overflow errors,
190 this behavior is not the default.
193 controls the action taken when unsent messages
194 are queued on socket and a
197 If the socket promises reliable delivery of data and
200 the system will block the process on the
202 attempt until it is able to transmit the data or until it decides it
203 is unable to deliver the information (a timeout period, termed the
204 linger interval, is specified in seconds in the
213 is issued, the system will process the close in a manner that allows
214 the process to continue as quickly as possible.
218 requests permission to send broadcast datagrams
220 Broadcast was a privileged operation in earlier versions of the system.
221 With protocols that support out-of-band data, the
224 requests that out-of-band data be placed in the normal data input queue
225 as received; it will then be accessible with
232 Some protocols always behave as if this option is set.
236 are options to adjust the normal
237 buffer sizes allocated for output and input buffers, respectively.
238 The buffer size may be increased for high-volume connections,
239 or may be decreased to limit the possible backlog of incoming data.
240 The system places an absolute maximum on these values, which is accessible
244 .Va kern.ipc.maxsockbuf .
247 is an option to set the minimum count for output operations.
248 Most output operations process all of the data supplied
249 by the call, delivering data to the protocol for transmission
250 and blocking as necessary for flow control.
251 Nonblocking output operations will process as much data as permitted
252 subject to flow control without blocking, but will process no data
253 if flow control does not allow the smaller of the low water mark value
254 or the entire request to be processed.
257 operation testing the ability to write to a socket will return true
258 only if the low water mark amount could be processed.
259 The default value for
261 is set to a convenient size for network efficiency, often 1024.
263 is an option to set the minimum count for input operations.
264 In general, receive calls will block until any (non-zero) amount of data
265 is received, then return with the smaller of the amount available or the amount
267 The default value for
272 is set to a larger value, blocking receive calls normally
273 wait until they have received the smaller of the low water mark value
274 or the requested amount.
275 Receive calls may still return less than the low water mark if an error
276 occurs, a signal is caught, or the type of data next in the receive queue
277 is different from that which was returned.
280 is an option to set a timeout value for output operations.
283 parameter with the number of seconds and microseconds
284 used to limit waits for output operations to complete.
285 If a send operation has blocked for this much time,
286 it returns with a partial count
289 if no data were sent.
290 In the current implementation, this timer is restarted each time additional
291 data are delivered to the protocol,
292 implying that the limit applies to output portions ranging in size
293 from the low water mark to the high water mark for output.
295 is an option to set a timeout value for input operations.
298 parameter with the number of seconds and microseconds
299 used to limit waits for input operations to complete.
300 In the current implementation, this timer is restarted each time additional
301 data are received by the protocol,
302 and thus the limit is in effect an inactivity timer.
303 If a receive operation has been blocked for this much time without
304 receiving additional data, it returns with a short count
307 if no data were received.
313 which will filter incoming connections
314 on a listening stream socket before being presented for
318 must be called on the socket before
319 trying to install the filter on it,
324 struct accept_filter_arg {
332 .Fa struct accept_filter_arg
333 that will select and configure the
334 .Xr accept_filter 9 .
336 should be filled with the name of the accept filter
337 that the application wishes to place on the listening socket.
339 is an optional parameter that can be passed to the accept
342 to provide additional configuration options at attach time.
345 of NULL will remove the filter.
351 are options used only with
354 returns the type of the socket, such as
356 it is useful for servers that inherit sockets on startup.
358 returns any pending error on the socket and clears
360 It may be used to check for asynchronous errors on connected
361 datagram sockets or for other asynchronous errors.
365 The call succeeds unless:
370 is not a valid descriptor.
374 is a file, not a socket.
375 .It Bq Er ENOPROTOOPT
376 The option is unknown at the level indicated.
378 The address pointed to by
380 is not in a valid part of the process address space.
383 this error may also be returned if
385 is not in a valid part of the process address space.
389 on a non-listening socket was attempted.
402 system call appeared in
405 Several of the socket options should be handled at lower levels of the system.