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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)"
190 enables debugging in the underlying protocol modules.
192 indicates that the rules used in validating addresses supplied
195 system call should allow reuse of local addresses.
197 allows completely duplicate bindings by multiple processes
200 before binding the port.
201 This option permits multiple instances of a program to each
202 receive UDP/IP multicast or broadcast datagrams destined for the bound port.
205 periodic transmission of messages on a connected socket.
207 connected party fail to respond to these messages, the connection is
208 considered broken and processes using the socket are notified via a
210 signal when attempting to send data.
212 indicates that outgoing messages should
213 bypass the standard routing facilities.
214 Instead, messages are directed
215 to the appropriate network interface according to the network portion
216 of the destination address.
219 controls the action taken when unsent messages
220 are queued on socket and a
223 If the socket promises reliable delivery of data and
226 the system will block the process on the
228 attempt until it is able to transmit the data or until it decides it
229 is unable to deliver the information (a timeout period, termed the
230 linger interval, is specified in seconds in the
239 is issued, the system will process the close in a manner that allows
240 the process to continue as quickly as possible.
244 requests permission to send broadcast datagrams
246 Broadcast was a privileged operation in earlier versions of the system.
247 With protocols that support out-of-band data, the
250 requests that out-of-band data be placed in the normal data input queue
251 as received; it will then be accessible with
258 Some protocols always behave as if this option is set.
262 are options to adjust the normal
263 buffer sizes allocated for output and input buffers, respectively.
264 The buffer size may be increased for high-volume connections,
265 or may be decreased to limit the possible backlog of incoming data.
266 The system places an absolute maximum on these values, which is accessible
270 .Dq Li kern.ipc.maxsockbuf .
273 is an option to set the minimum count for output operations.
274 Most output operations process all of the data supplied
275 by the call, delivering data to the protocol for transmission
276 and blocking as necessary for flow control.
277 Nonblocking output operations will process as much data as permitted
278 subject to flow control without blocking, but will process no data
279 if flow control does not allow the smaller of the low water mark value
280 or the entire request to be processed.
283 operation testing the ability to write to a socket will return true
284 only if the low water mark amount could be processed.
285 The default value for
287 is set to a convenient size for network efficiency, often 1024.
289 is an option to set the minimum count for input operations.
290 In general, receive calls will block until any (non-zero) amount of data
291 is received, then return with the smaller of the amount available or the amount
293 The default value for
298 is set to a larger value, blocking receive calls normally
299 wait until they have received the smaller of the low water mark value
300 or the requested amount.
301 Receive calls may still return less than the low water mark if an error
302 occurs, a signal is caught, or the type of data next in the receive queue
303 is different from that which was returned.
306 is an option to set a timeout value for output operations.
309 argument with the number of seconds and microseconds
310 used to limit waits for output operations to complete.
311 If a send operation has blocked for this much time,
312 it returns with a partial count
315 if no data were sent.
316 In the current implementation, this timer is restarted each time additional
317 data are delivered to the protocol,
318 implying that the limit applies to output portions ranging in size
319 from the low water mark to the high water mark for output.
321 is an option to set a timeout value for input operations.
324 argument with the number of seconds and microseconds
325 used to limit waits for input operations to complete.
326 In the current implementation, this timer is restarted each time additional
327 data are received by the protocol,
328 and thus the limit is in effect an inactivity timer.
329 If a receive operation has been blocked for this much time without
330 receiving additional data, it returns with a short count
333 if no data were received.
336 can be used to over-ride the default FIB (routing table) for the given socket.
337 The value must be from 0 to one less than the number returned from
345 which will filter incoming connections
346 on a listening stream socket before being presented for
350 must be called on the socket before
351 trying to install the filter on it,
354 system call will fail.
356 struct accept_filter_arg {
366 .Fa struct accept_filter_arg
367 that will select and configure the
368 .Xr accept_filter 9 .
372 should be filled with the name of the accept filter
373 that the application wishes to place on the listening socket.
374 The optional argument
376 can be passed to the accept
379 to provide additional configuration options at attach time.
382 of NULL will remove the filter.
386 option controls generation of the
389 when writing to a connected socket where the other end has been
390 closed returns with the error
397 option is enabled on a
401 call will return a timestamp corresponding to when the datagram was received.
406 structure points to a buffer that contains a
408 structure followed by a
418 fields have the following values for TIMESTAMP:
420 cmsg_len = sizeof(struct timeval);
421 cmsg_level = SOL_SOCKET;
422 cmsg_type = SCM_TIMESTAMP;
428 cmsg_len = sizeof(struct bintime);
429 cmsg_level = SOL_SOCKET;
430 cmsg_type = SCM_BINTIME;
437 are options used only with
440 returns whether the socket is currently accepting connections,
441 that is, whether or not the
443 system call was invoked on the socket.
445 returns the type of the socket, such as
447 it is useful for servers that inherit sockets on startup.
449 returns any pending error on the socket and clears
451 It may be used to check for asynchronous errors on connected
452 datagram sockets or for other asynchronous errors.
456 returns the MAC label of the socket.
458 returns the MAC label of the socket's peer.
459 Note that your kernel must be compiled with MAC support.
462 for more information.
464 returns the maximal number of queued connections, as set by
467 returns the number of unaccepted complete connections.
469 returns the number of unaccepted incomplete connections.
473 The call succeeds unless:
478 is not a valid descriptor.
482 is a file, not a socket.
483 .It Bq Er ENOPROTOOPT
484 The option is unknown at the level indicated.
486 The address pointed to by
488 is not in a valid part of the process address space.
491 this error may also be returned if
493 is not in a valid part of the process address space.
497 on a non-listening socket was attempted.
513 .Xr accept_filter 9 ,
518 system call appeared in
521 Several of the socket options should be handled at lower levels of the system.