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28 .\" @(#)getsockopt.2 8.4 (Berkeley) 5/2/95
31 .Dd September 11, 2019
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_REUSEPORT_LB Ta "enables duplicate address and port bindings with load balancing"
156 .It Dv SO_KEEPALIVE Ta "enables keep connections alive"
157 .It Dv SO_DONTROUTE Ta "enables routing bypass for outgoing messages"
158 .It Dv SO_LINGER Ta "linger on close if data present"
159 .It Dv SO_BROADCAST Ta "enables permission to transmit broadcast messages"
160 .It Dv SO_OOBINLINE Ta "enables reception of out-of-band data in band"
161 .It Dv SO_SNDBUF Ta "set buffer size for output"
162 .It Dv SO_RCVBUF Ta "set buffer size for input"
163 .It Dv SO_SNDLOWAT Ta "set minimum count for output"
164 .It Dv SO_RCVLOWAT Ta "set minimum count for input"
165 .It Dv SO_SNDTIMEO Ta "set timeout value for output"
166 .It Dv SO_RCVTIMEO Ta "set timeout value for input"
167 .It Dv SO_ACCEPTFILTER Ta "set accept filter on listening socket"
168 .It Dv SO_NOSIGPIPE Ta
169 controls generation of
172 .It Dv SO_TIMESTAMP Ta "enables reception of a timestamp with datagrams"
173 .It Dv SO_BINTIME Ta "enables reception of a timestamp with datagrams"
174 .It Dv SO_ACCEPTCONN Ta "get listening status of the socket (get only)"
175 .It Dv SO_DOMAIN Ta "get the domain of the socket (get only)"
176 .It Dv SO_TYPE Ta "get the type of the socket (get only)"
177 .It Dv SO_PROTOCOL Ta "get the protocol number for the socket (get only)"
178 .It Dv SO_PROTOTYPE Ta "SunOS alias for the Linux SO_PROTOCOL (get only)"
179 .It Dv SO_ERROR Ta "get and clear error on the socket (get only)"
180 .It Dv SO_SETFIB Ta "set the associated FIB (routing table) for the socket (set only)"
183 The following options are recognized in
185 .Bl -column SO_LISTENINCQLEN -offset indent
186 .It Dv SO_LABEL Ta "get MAC label of the socket (get only)"
187 .It Dv SO_PEERLABEL Ta "get socket's peer's MAC label (get only)"
188 .It Dv SO_LISTENQLIMIT Ta "get backlog limit of the socket (get only)"
189 .It Dv SO_LISTENQLEN Ta "get complete queue length of the socket (get only)"
190 .It Dv SO_LISTENINCQLEN Ta "get incomplete queue length of the socket (get only)"
191 .It Dv SO_USER_COOKIE Ta "set the 'so_user_cookie' value for the socket (uint32_t, set only)"
192 .It Dv SO_TS_CLOCK Ta "set specific format of timestamp returned by SO_TIMESTAMP"
193 .It Dv SO_MAX_PACING_RATE Ta "set the maximum transmit rate in bytes per second for the socket"
197 enables debugging in the underlying protocol modules.
200 indicates that the rules used in validating addresses supplied
203 system call should allow reuse of local addresses.
206 allows completely duplicate bindings by multiple processes
209 before binding the port.
210 This option permits multiple instances of a program to each
211 receive UDP/IP multicast or broadcast datagrams destined for the bound port.
214 allows completely duplicate bindings by multiple processes
217 before binding the port.
218 Incoming TCP and UDP connections are distributed among the sharing
219 processes based on a hash function of local port number, foreign IP
220 address and port number. A maximum of 256 processes can share one socket.
224 periodic transmission of messages on a connected socket.
226 connected party fail to respond to these messages, the connection is
227 considered broken and processes using the socket are notified via a
229 signal when attempting to send data.
232 indicates that outgoing messages should
233 bypass the standard routing facilities.
234 Instead, messages are directed
235 to the appropriate network interface according to the network portion
236 of the destination address.
239 controls the action taken when unsent messages
240 are queued on socket and a
243 If the socket promises reliable delivery of data and
246 the system will block the process on the
248 attempt until it is able to transmit the data or until it decides it
249 is unable to deliver the information (a timeout period, termed the
250 linger interval, is specified in seconds in the
259 is issued, the system will process the close in a manner that allows
260 the process to continue as quickly as possible.
264 requests permission to send broadcast datagrams
266 Broadcast was a privileged operation in earlier versions of the system.
268 With protocols that support out-of-band data, the
271 requests that out-of-band data be placed in the normal data input queue
272 as received; it will then be accessible with
279 Some protocols always behave as if this option is set.
284 are options to adjust the normal
285 buffer sizes allocated for output and input buffers, respectively.
286 The buffer size may be increased for high-volume connections,
287 or may be decreased to limit the possible backlog of incoming data.
288 The system places an absolute maximum on these values, which is accessible
292 .Dq Li kern.ipc.maxsockbuf .
295 is an option to set the minimum count for output operations.
296 Most output operations process all of the data supplied
297 by the call, delivering data to the protocol for transmission
298 and blocking as necessary for flow control.
299 Nonblocking output operations will process as much data as permitted
300 subject to flow control without blocking, but will process no data
301 if flow control does not allow the smaller of the low water mark value
302 or the entire request to be processed.
305 operation testing the ability to write to a socket will return true
306 only if the low water mark amount could be processed.
307 The default value for
309 is set to a convenient size for network efficiency, often 1024.
312 is an option to set the minimum count for input operations.
313 In general, receive calls will block until any (non-zero) amount of data
314 is received, then return with the smaller of the amount available or the amount
316 The default value for
321 is set to a larger value, blocking receive calls normally
322 wait until they have received the smaller of the low water mark value
323 or the requested amount.
324 Receive calls may still return less than the low water mark if an error
325 occurs, a signal is caught, or the type of data next in the receive queue
326 is different from that which was returned.
329 is an option to set a timeout value for output operations.
332 argument with the number of seconds and microseconds
333 used to limit waits for output operations to complete.
334 If a send operation has blocked for this much time,
335 it returns with a partial count
338 if no data were sent.
339 In the current implementation, this timer is restarted each time additional
340 data are delivered to the protocol,
341 implying that the limit applies to output portions ranging in size
342 from the low water mark to the high water mark for output.
345 is an option to set a timeout value for input operations.
348 argument with the number of seconds and microseconds
349 used to limit waits for input operations to complete.
350 In the current implementation, this timer is restarted each time additional
351 data are received by the protocol,
352 and thus the limit is in effect an inactivity timer.
353 If a receive operation has been blocked for this much time without
354 receiving additional data, it returns with a short count
357 if no data were received.
360 can be used to over-ride the default FIB (routing table) for the given socket.
361 The value must be from 0 to one less than the number returned from
366 can be used to set the uint32_t so_user_cookie field in the socket.
367 The value is an uint32_t, and can be used in the kernel code that
368 manipulates traffic related to the socket.
369 The default value for the field is 0.
370 As an example, the value can be used as the skipto target or
378 which will filter incoming connections
379 on a listening stream socket before being presented for
383 must be called on the socket before
384 trying to install the filter on it,
387 system call will fail.
389 struct accept_filter_arg {
399 .Fa struct accept_filter_arg
400 that will select and configure the
401 .Xr accept_filter 9 .
405 should be filled with the name of the accept filter
406 that the application wishes to place on the listening socket.
407 The optional argument
409 can be passed to the accept
412 to provide additional configuration options at attach time.
415 of NULL will remove the filter.
419 option controls generation of the
422 when writing to a connected socket where the other end has been
423 closed returns with the error
430 option is enabled on a
434 call may return a timestamp corresponding to when the datagram was received.
435 However, it may not, for example due to a resource shortage.
440 structure points to a buffer that contains a
442 structure followed by a
452 fields have the following values for TIMESTAMP by default:
454 cmsg_len = CMSG_LEN(sizeof(struct timeval));
455 cmsg_level = SOL_SOCKET;
456 cmsg_type = SCM_TIMESTAMP;
462 cmsg_len = CMSG_LEN(sizeof(struct bintime));
463 cmsg_level = SOL_SOCKET;
464 cmsg_type = SCM_BINTIME;
467 Additional timestamp types are available by following
471 which requests a specific timestamp format to be returned instead of
472 .Dv SCM_TIMESTAMP when
473 .Dv SO_TIMESTAMP is enabled.
476 values are recognized in
478 .Bl -column SO_TS_CLOCK -offset indent
479 .It Dv SO_TS_REALTIME_MICRO Ta "realtime (SCM_TIMESTAMP, struct timeval), default"
480 .It Dv SO_TS_BINTIME Ta "realtime (SCM_BINTIME, struct bintime)"
481 .It Dv SO_TS_REALTIME Ta "realtime (SCM_REALTIME, struct timespec)"
482 .It Dv SO_TS_MONOTONIC Ta "monotonic time (SCM_MONOTONIC, struct timespec)"
492 are options used only with
495 returns whether the socket is currently accepting connections,
496 that is, whether or not the
498 system call was invoked on the socket.
500 returns the type of the socket, such as
502 it is useful for servers that inherit sockets on startup.
504 returns the protocol number for the socket, for
510 returns any pending error on the socket and clears
512 It may be used to check for asynchronous errors on connected
513 datagram sockets or for other asynchronous errors.
517 returns the MAC label of the socket.
519 returns the MAC label of the socket's peer.
520 Note that your kernel must be compiled with MAC support.
523 for more information.
525 returns the maximal number of queued connections, as set by
528 returns the number of unaccepted complete connections.
530 returns the number of unaccepted incomplete connections.
532 .Dv SO_MAX_PACING_RATE
533 instruct the socket and underlying network adapter layers to limit the
534 transfer rate to the given unsigned 32-bit value in bytes per second.
542 system calls succeed unless:
547 is not a valid descriptor.
551 is a file, not a socket.
552 .It Bq Er ENOPROTOOPT
553 The option is unknown at the level indicated.
555 The address pointed to by
557 is not in a valid part of the process address space.
560 this error may also be returned if
562 is not in a valid part of the process address space.
566 on a non-listening socket was attempted.
568 A memory allocation failed that was required to service the request.
573 system call may also return the following error:
576 Insufficient resources were available in the system
577 to perform the operation.
593 .Xr accept_filter 9 ,
600 system calls appeared in
603 Several of the socket options should be handled at lower levels of the system.