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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 $
30 .\" $DragonFly: src/lib/libc/sys/getsockopt.2,v 1.5 2007/07/14 21:48:15 swildner Exp $
38 .Nd get and set options on sockets
45 .Fn getsockopt "int s" "int level" "int optname" "void *optval" "socklen_t *optlen"
47 .Fn setsockopt "int s" "int level" "int optname" "const void *optval" "socklen_t optlen"
54 associated with a socket. Options may exist at multiple
55 protocol levels; they are always present at the uppermost
59 When manipulating socket options the level at which the
60 option resides and the name of the option must be specified.
61 To manipulate options at the socket level,
65 To manipulate options at any
66 other level the protocol number of the appropriate protocol
67 controlling the option is supplied. For example,
68 to indicate that an option is to be interpreted by the
72 should be set to the protocol number of
81 are used to access option values for
85 they identify a buffer in which the value for the
86 requested option(s) are to be returned. For
89 is a value-result parameter, initially containing the
90 size of the buffer pointed to by
92 and modified on return to indicate the actual size of
93 the value returned. If no option value is
94 to be supplied or returned,
99 and any specified options are passed uninterpreted to the appropriate
100 protocol module for interpretation.
103 contains definitions for
104 socket level options, described below.
105 Options at other protocol levels vary in format and
106 name; consult the appropriate entries in
110 Most socket-level options utilize an
116 the parameter should be non-zero to enable a boolean option,
117 or zero if the option is to be disabled.
121 parameter, defined in
123 which specifies the desired state of the option and the
124 linger interval (see below).
130 parameter, defined in
133 The following options are recognized at the socket level.
134 Except as noted, each may be examined with
138 .Bl -column SO_ACCEPTFILTER -offset indent
139 .It Dv SO_DEBUG Ta "enables recording of debugging information"
140 .It Dv SO_REUSEADDR Ta "enables local address reuse"
141 .It Dv SO_REUSEPORT Ta "enables duplicate address and port bindings"
142 .It Dv SO_KEEPALIVE Ta "enables keep connections alive"
143 .It Dv SO_DONTROUTE Ta "enables routing bypass for outgoing messages"
144 .It Dv SO_LINGER Ta "linger on close if data present"
145 .It Dv SO_BROADCAST Ta "enables permission to transmit broadcast messages"
146 .It Dv SO_OOBINLINE Ta "enables reception of out-of-band data in band"
147 .It Dv SO_SNDBUF Ta "set buffer size for output"
148 .It Dv SO_RCVBUF Ta "set buffer size for input"
149 .It Dv SO_SNDLOWAT Ta "set minimum count for output"
150 .It Dv SO_RCVLOWAT Ta "set minimum count for input"
151 .It Dv SO_SNDTIMEO Ta "set timeout value for output"
152 .It Dv SO_RCVTIMEO Ta "set timeout value for input"
153 .It Dv SO_ACCEPTFILTER Ta "set accept filter on listening socket"
154 .It Dv SO_TYPE Ta "get the type of the socket (get only)"
155 .It Dv SO_ERROR Ta "get and clear error on the socket (get only)"
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.
186 controls the action taken when unsent messages
187 are queued on socket and a
190 If the socket promises reliable delivery of data and
193 the system will block the process on the
195 attempt until it is able to transmit the data or until it decides it
196 is unable to deliver the information (a timeout period, termed the
197 linger interval, is specified in seconds in the
206 is issued, the system will process the close in a manner that allows
207 the process to continue as quickly as possible.
211 requests permission to send broadcast datagrams
213 Broadcast was a privileged operation in earlier versions of the system.
214 With protocols that support out-of-band data, the
217 requests that out-of-band data be placed in the normal data input queue
218 as received; it will then be accessible with
225 Some protocols always behave as if this option is set.
229 are options to adjust the normal
230 buffer sizes allocated for output and input buffers, respectively.
231 The buffer size may be increased for high-volume connections,
232 or may be decreased to limit the possible backlog of incoming data.
233 The system places an absolute maximum on these values, which is accessible
237 .Va kern.ipc.maxsockbuf .
240 is an option to set the minimum count for output operations.
241 Most output operations process all of the data supplied
242 by the call, delivering data to the protocol for transmission
243 and blocking as necessary for flow control.
244 Nonblocking output operations will process as much data as permitted
245 subject to flow control without blocking, but will process no data
246 if flow control does not allow the smaller of the low water mark value
247 or the entire request to be processed.
250 operation testing the ability to write to a socket will return true
251 only if the low water mark amount could be processed.
252 The default value for
254 is set to a convenient size for network efficiency, often 1024.
256 is an option to set the minimum count for input operations.
257 In general, receive calls will block until any (non-zero) amount of data
258 is received, then return with the smaller of the amount available or the amount
260 The default value for
265 is set to a larger value, blocking receive calls normally
266 wait until they have received the smaller of the low water mark value
267 or the requested amount.
268 Receive calls may still return less than the low water mark if an error
269 occurs, a signal is caught, or the type of data next in the receive queue
270 is different from that which was returned.
273 is an option to set a timeout value for output operations.
276 parameter with the number of seconds and microseconds
277 used to limit waits for output operations to complete.
278 If a send operation has blocked for this much time,
279 it returns with a partial count
282 if no data were sent.
283 In the current implementation, this timer is restarted each time additional
284 data are delivered to the protocol,
285 implying that the limit applies to output portions ranging in size
286 from the low water mark to the high water mark for output.
288 is an option to set a timeout value for input operations.
291 parameter with the number of seconds and microseconds
292 used to limit waits for input operations to complete.
293 In the current implementation, this timer is restarted each time additional
294 data are received by the protocol,
295 and thus the limit is in effect an inactivity timer.
296 If a receive operation has been blocked for this much time without
297 receiving additional data, it returns with a short count
300 if no data were received.
306 which will filter incoming connections
307 on a listening stream socket before being presented for
311 must be called on the socket before
312 trying to install the filter on it,
317 struct accept_filter_arg {
325 .Fa struct accept_filter_arg
326 that will select and configure the
327 .Xr accept_filter 9 .
329 should be filled with the name of the accept filter
330 that the application wishes to place on the listening socket.
332 is an optional parameter that can be passed to the accept
335 to provide additional configuration options at attach time.
338 of NULL will remove the filter.
344 are options used only with
347 returns the type of the socket, such as
349 it is useful for servers that inherit sockets on startup.
351 returns any pending error on the socket and clears
353 It may be used to check for asynchronous errors on connected
354 datagram sockets or for other asynchronous errors.
358 The call succeeds unless:
363 is not a valid descriptor.
367 is a file, not a socket.
368 .It Bq Er ENOPROTOOPT
369 The option is unknown at the level indicated.
371 The address pointed to by
373 is not in a valid part of the process address space.
376 this error may also be returned if
378 is not in a valid part of the process address space.
382 on a non-listening socket was attempted.
395 system call appeared in
398 Several of the socket options should be handled at lower levels of the system.