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28 .\" @(#)getsockopt.2 8.4 (Berkeley) 5/2/95
37 .Nd get and set options on sockets
44 .Fn getsockopt "int s" "int level" "int optname" "void * restrict optval" "socklen_t * restrict optlen"
46 .Fn setsockopt "int s" "int level" "int optname" "const void *optval" "socklen_t optlen"
55 associated with a socket.
56 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.
71 to indicate that an option is to be interpreted by the
75 should be set to the protocol number of
85 are used to access option values for
89 they identify a buffer in which the value for the
90 requested option(s) are to be returned.
94 is a value-result argument, initially containing the
95 size of the buffer pointed to by
97 and modified on return to indicate the actual size of
100 to be supplied or returned,
107 and any specified options are passed uninterpreted to the appropriate
108 protocol module for interpretation.
111 contains definitions for
112 socket level options, described below.
113 Options at other protocol levels vary in format and
114 name; consult the appropriate entries in
118 Most socket-level options utilize an
124 the argument should be non-zero to enable a boolean option,
125 or zero if the option is to be disabled.
131 which specifies the desired state of the option and the
132 linger interval (see below).
141 The following options are recognized at the socket level.
142 For protocol-specific options, see protocol manual pages,
147 Except as noted, each may be examined with
151 .Bl -column SO_ACCEPTFILTER -offset indent
152 .It Dv SO_DEBUG Ta "enables recording of debugging information"
153 .It Dv SO_REUSEADDR Ta "enables local address reuse"
154 .It Dv SO_REUSEPORT Ta "enables duplicate address and port bindings"
155 .It Dv SO_KEEPALIVE Ta "enables keep connections alive"
156 .It Dv SO_DONTROUTE Ta "enables routing bypass for outgoing messages"
157 .It Dv SO_LINGER Ta "linger on close if data present"
158 .It Dv SO_BROADCAST Ta "enables permission to transmit broadcast messages"
159 .It Dv SO_OOBINLINE Ta "enables reception of out-of-band data in band"
160 .It Dv SO_SNDBUF Ta "set buffer size for output"
161 .It Dv SO_RCVBUF Ta "set buffer size for input"
162 .It Dv SO_SNDLOWAT Ta "set minimum count for output"
163 .It Dv SO_RCVLOWAT Ta "set minimum count for input"
164 .It Dv SO_SNDTIMEO Ta "set timeout value for output"
165 .It Dv SO_RCVTIMEO Ta "set timeout value for input"
166 .It Dv SO_ACCEPTFILTER Ta "set accept filter on listening socket"
167 .It Dv SO_NOSIGPIPE Ta
168 controls generation of
171 .It Dv SO_TIMESTAMP Ta "enables reception of a timestamp with datagrams"
172 .It Dv SO_BINTIME Ta "enables reception of a timestamp with datagrams"
173 .It Dv SO_ACCEPTCONN Ta "get listening status of the socket (get only)"
174 .It Dv SO_TYPE Ta "get the type of the socket (get only)"
175 .It Dv SO_ERROR Ta "get and clear error on the socket (get only)"
176 .It Dv SO_SETFIB Ta "set the associated FIB (routing table) for the socket (set only)"
179 The following options are recognized in
181 .Bl -column SO_LISTENINCQLEN -offset indent
182 .It Dv SO_LABEL Ta "get MAC label of the socket (get only)"
183 .It Dv SO_PEERLABEL Ta "get socket's peer's MAC label (get only)"
184 .It Dv SO_LISTENQLIMIT Ta "get backlog limit of the socket (get only)"
185 .It Dv SO_LISTENQLEN Ta "get complete queue length of the socket (get only)"
186 .It Dv SO_LISTENINCQLEN Ta "get incomplete queue length of the socket (get only)"
187 .It Dv SO_USER_COOKIE Ta "set the 'so_user_cookie' value for the socket (uint32_t, set only)"
191 enables debugging in the underlying protocol modules.
194 indicates that the rules used in validating addresses supplied
197 system call should allow reuse of local addresses.
200 allows completely duplicate bindings by multiple processes
203 before binding the port.
204 This option permits multiple instances of a program to each
205 receive UDP/IP multicast or broadcast datagrams destined for the bound port.
209 periodic transmission of messages on a connected socket.
211 connected party fail to respond to these messages, the connection is
212 considered broken and processes using the socket are notified via a
214 signal when attempting to send data.
217 indicates that outgoing messages should
218 bypass the standard routing facilities.
219 Instead, messages are directed
220 to the appropriate network interface according to the network portion
221 of the destination address.
224 controls the action taken when unsent messages
225 are queued on socket and a
228 If the socket promises reliable delivery of data and
231 the system will block the process on the
233 attempt until it is able to transmit the data or until it decides it
234 is unable to deliver the information (a timeout period, termed the
235 linger interval, is specified in seconds in the
244 is issued, the system will process the close in a manner that allows
245 the process to continue as quickly as possible.
249 requests permission to send broadcast datagrams
251 Broadcast was a privileged operation in earlier versions of the system.
253 With protocols that support out-of-band data, the
256 requests that out-of-band data be placed in the normal data input queue
257 as received; it will then be accessible with
264 Some protocols always behave as if this option is set.
269 are options to adjust the normal
270 buffer sizes allocated for output and input buffers, respectively.
271 The buffer size may be increased for high-volume connections,
272 or may be decreased to limit the possible backlog of incoming data.
273 The system places an absolute maximum on these values, which is accessible
277 .Dq Li kern.ipc.maxsockbuf .
280 is an option to set the minimum count for output operations.
281 Most output operations process all of the data supplied
282 by the call, delivering data to the protocol for transmission
283 and blocking as necessary for flow control.
284 Nonblocking output operations will process as much data as permitted
285 subject to flow control without blocking, but will process no data
286 if flow control does not allow the smaller of the low water mark value
287 or the entire request to be processed.
290 operation testing the ability to write to a socket will return true
291 only if the low water mark amount could be processed.
292 The default value for
294 is set to a convenient size for network efficiency, often 1024.
297 is an option to set the minimum count for input operations.
298 In general, receive calls will block until any (non-zero) amount of data
299 is received, then return with the smaller of the amount available or the amount
301 The default value for
306 is set to a larger value, blocking receive calls normally
307 wait until they have received the smaller of the low water mark value
308 or the requested amount.
309 Receive calls may still return less than the low water mark if an error
310 occurs, a signal is caught, or the type of data next in the receive queue
311 is different from that which was returned.
314 is an option to set a timeout value for output operations.
317 argument with the number of seconds and microseconds
318 used to limit waits for output operations to complete.
319 If a send operation has blocked for this much time,
320 it returns with a partial count
323 if no data were sent.
324 In the current implementation, this timer is restarted each time additional
325 data are delivered to the protocol,
326 implying that the limit applies to output portions ranging in size
327 from the low water mark to the high water mark for output.
330 is an option to set a timeout value for input operations.
333 argument with the number of seconds and microseconds
334 used to limit waits for input operations to complete.
335 In the current implementation, this timer is restarted each time additional
336 data are received by the protocol,
337 and thus the limit is in effect an inactivity timer.
338 If a receive operation has been blocked for this much time without
339 receiving additional data, it returns with a short count
342 if no data were received.
345 can be used to over-ride the default FIB (routing table) for the given socket.
346 The value must be from 0 to one less than the number returned from
351 can be used to set the uint32_t so_user_cookie field in the socket.
352 The value is an uint32_t, and can be used in the kernel code that
353 manipulates traffic related to the socket.
354 The default value for the field is 0.
355 As an example, the value can be used as the skipto target or
363 which will filter incoming connections
364 on a listening stream socket before being presented for
368 must be called on the socket before
369 trying to install the filter on it,
372 system call will fail.
374 struct accept_filter_arg {
384 .Fa struct accept_filter_arg
385 that will select and configure the
386 .Xr accept_filter 9 .
390 should be filled with the name of the accept filter
391 that the application wishes to place on the listening socket.
392 The optional argument
394 can be passed to the accept
397 to provide additional configuration options at attach time.
400 of NULL will remove the filter.
404 option controls generation of the
407 when writing to a connected socket where the other end has been
408 closed returns with the error
415 option is enabled on a
419 call will return a timestamp corresponding to when the datagram was received.
424 structure points to a buffer that contains a
426 structure followed by a
436 fields have the following values for TIMESTAMP:
438 cmsg_len = sizeof(struct timeval);
439 cmsg_level = SOL_SOCKET;
440 cmsg_type = SCM_TIMESTAMP;
446 cmsg_len = sizeof(struct bintime);
447 cmsg_level = SOL_SOCKET;
448 cmsg_type = SCM_BINTIME;
455 are options used only with
458 returns whether the socket is currently accepting connections,
459 that is, whether or not the
461 system call was invoked on the socket.
463 returns the type of the socket, such as
465 it is useful for servers that inherit sockets on startup.
467 returns any pending error on the socket and clears
469 It may be used to check for asynchronous errors on connected
470 datagram sockets or for other asynchronous errors.
474 returns the MAC label of the socket.
476 returns the MAC label of the socket's peer.
477 Note that your kernel must be compiled with MAC support.
480 for more information.
482 returns the maximal number of queued connections, as set by
485 returns the number of unaccepted complete connections.
487 returns the number of unaccepted incomplete connections.
491 The call succeeds unless:
496 is not a valid descriptor.
500 is a file, not a socket.
501 .It Bq Er ENOPROTOOPT
502 The option is unknown at the level indicated.
504 The address pointed to by
506 is not in a valid part of the process address space.
509 this error may also be returned if
511 is not in a valid part of the process address space.
515 on a non-listening socket was attempted.
531 .Xr accept_filter 9 ,
536 system call appeared in
539 Several of the socket options should be handled at lower levels of the system.