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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_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_RERROR Ta "enables receive error reporting"
181 .It Dv SO_SETFIB Ta "set the associated FIB (routing table) for the socket (set only)"
184 The following options are recognized in
186 .Bl -column SO_LISTENINCQLEN -offset indent
187 .It Dv SO_LABEL Ta "get MAC label of the socket (get only)"
188 .It Dv SO_PEERLABEL Ta "get socket's peer's MAC label (get only)"
189 .It Dv SO_LISTENQLIMIT Ta "get backlog limit of the socket (get only)"
190 .It Dv SO_LISTENQLEN Ta "get complete queue length of the socket (get only)"
191 .It Dv SO_LISTENINCQLEN Ta "get incomplete queue length of the socket (get only)"
192 .It Dv SO_USER_COOKIE Ta "set the 'so_user_cookie' value for the socket (uint32_t, set only)"
193 .It Dv SO_TS_CLOCK Ta "set specific format of timestamp returned by SO_TIMESTAMP"
194 .It Dv SO_MAX_PACING_RATE Ta "set the maximum transmit rate in bytes per second for the socket"
195 .It Dv SO_NO_OFFLOAD Ta "disables protocol offloads"
196 .It Dv SO_NO_DDP Ta "disables direct data placement offload"
200 enables debugging in the underlying protocol modules.
203 indicates that the rules used in validating addresses supplied
206 system call should allow reuse of local addresses.
209 allows completely duplicate bindings by multiple processes
212 before binding the port.
213 This option permits multiple instances of a program to each
214 receive UDP/IP multicast or broadcast datagrams destined for the bound port.
217 allows completely duplicate bindings by multiple processes
220 before binding the port.
221 Incoming TCP and UDP connections are distributed among the sharing
222 processes based on a hash function of local port number, foreign IP
223 address and port number.
224 A maximum of 256 processes can share one socket.
228 periodic transmission of messages on a connected socket.
230 connected party fail to respond to these messages, the connection is
231 considered broken and processes using the socket are notified via a
233 signal when attempting to send data.
236 indicates that outgoing messages should
237 bypass the standard routing facilities.
238 Instead, messages are directed
239 to the appropriate network interface according to the network portion
240 of the destination address.
243 controls the action taken when unsent messages
244 are queued on socket and a
247 If the socket promises reliable delivery of data and
250 the system will block the process on the
252 attempt until it is able to transmit the data or until it decides it
253 is unable to deliver the information (a timeout period, termed the
254 linger interval, is specified in seconds in the
263 is issued, the system will process the close in a manner that allows
264 the process to continue as quickly as possible.
268 requests permission to send broadcast datagrams
270 Broadcast was a privileged operation in earlier versions of the system.
272 With protocols that support out-of-band data, the
275 requests that out-of-band data be placed in the normal data input queue
276 as received; it will then be accessible with
283 Some protocols always behave as if this option is set.
288 are options to adjust the normal
289 buffer sizes allocated for output and input buffers, respectively.
290 The buffer size may be increased for high-volume connections,
291 or may be decreased to limit the possible backlog of incoming data.
292 The system places an absolute maximum on these values, which is accessible
296 .Dq Li kern.ipc.maxsockbuf .
299 is an option to set the minimum count for output operations.
300 Most output operations process all of the data supplied
301 by the call, delivering data to the protocol for transmission
302 and blocking as necessary for flow control.
303 Nonblocking output operations will process as much data as permitted
304 subject to flow control without blocking, but will process no data
305 if flow control does not allow the smaller of the low water mark value
306 or the entire request to be processed.
309 operation testing the ability to write to a socket will return true
310 only if the low water mark amount could be processed.
311 The default value for
313 is set to a convenient size for network efficiency, often 1024.
316 is an option to set the minimum count for input operations.
317 In general, receive calls will block until any (non-zero) amount of data
318 is received, then return with the smaller of the amount available or the amount
320 The default value for
325 is set to a larger value, blocking receive calls normally
326 wait until they have received the smaller of the low water mark value
327 or the requested amount.
328 Receive calls may still return less than the low water mark if an error
329 occurs, a signal is caught, or the type of data next in the receive queue
330 is different from that which was returned.
333 is an option to set a timeout value for output operations.
336 argument with the number of seconds and microseconds
337 used to limit waits for output operations to complete.
338 If a send operation has blocked for this much time,
339 it returns with a partial count
342 if no data were sent.
343 In the current implementation, this timer is restarted each time additional
344 data are delivered to the protocol,
345 implying that the limit applies to output portions ranging in size
346 from the low water mark to the high water mark for output.
349 is an option to set a timeout value for input operations.
352 argument with the number of seconds and microseconds
353 used to limit waits for input operations to complete.
354 In the current implementation, this timer is restarted each time additional
355 data are received by the protocol,
356 and thus the limit is in effect an inactivity timer.
357 If a receive operation has been blocked for this much time without
358 receiving additional data, it returns with a short count
361 if no data were received.
364 can be used to over-ride the default FIB (routing table) for the given socket.
365 The value must be from 0 to one less than the number returned from
370 can be used to set the uint32_t so_user_cookie field in the socket.
371 The value is an uint32_t, and can be used in the kernel code that
372 manipulates traffic related to the socket.
373 The default value for the field is 0.
374 As an example, the value can be used as the skipto target or
382 which will filter incoming connections
383 on a listening stream socket before being presented for
387 must be called on the socket before
388 trying to install the filter on it,
391 system call will fail.
393 struct accept_filter_arg {
403 .Fa struct accept_filter_arg
404 that will select and configure the
405 .Xr accept_filter 9 .
409 should be filled with the name of the accept filter
410 that the application wishes to place on the listening socket.
411 The optional argument
413 can be passed to the accept
416 to provide additional configuration options at attach time.
419 of NULL will remove the filter.
423 option controls generation of the
426 when writing to a connected socket where the other end has been
427 closed returns with the error
434 option is enabled on a
438 call may return a timestamp corresponding to when the datagram was received.
439 However, it may not, for example due to a resource shortage.
444 structure points to a buffer that contains a
446 structure followed by a
456 fields have the following values for TIMESTAMP by default:
458 cmsg_len = CMSG_LEN(sizeof(struct timeval));
459 cmsg_level = SOL_SOCKET;
460 cmsg_type = SCM_TIMESTAMP;
466 cmsg_len = CMSG_LEN(sizeof(struct bintime));
467 cmsg_level = SOL_SOCKET;
468 cmsg_type = SCM_BINTIME;
471 Additional timestamp types are available by following
475 which requests a specific timestamp format to be returned instead of
476 .Dv SCM_TIMESTAMP when
477 .Dv SO_TIMESTAMP is enabled.
480 values are recognized in
482 .Bl -column SO_TS_CLOCK -offset indent
483 .It Dv SO_TS_REALTIME_MICRO Ta "realtime (SCM_TIMESTAMP, struct timeval), default"
484 .It Dv SO_TS_BINTIME Ta "realtime (SCM_BINTIME, struct bintime)"
485 .It Dv SO_TS_REALTIME Ta "realtime (SCM_REALTIME, struct timespec)"
486 .It Dv SO_TS_MONOTONIC Ta "monotonic time (SCM_MONOTONIC, struct timespec)"
496 are options used only with
499 returns whether the socket is currently accepting connections,
500 that is, whether or not the
502 system call was invoked on the socket.
504 returns the type of the socket, such as
506 it is useful for servers that inherit sockets on startup.
508 returns the protocol number for the socket, for
514 returns any pending error on the socket and clears
516 It may be used to check for asynchronous errors on connected
517 datagram sockets or for other asynchronous errors.
519 indicates that receive buffer overflows should be handled as errors.
520 Historically receive buffer overflows have been ignored and programs
521 could not tell if they missed messages or messages had been truncated
522 because of overflows.
523 Since programs historically do not expect to get receive overflow errors,
524 this behavior is not the default.
527 returns the MAC label of the socket.
529 returns the MAC label of the socket's peer.
530 Note that your kernel must be compiled with MAC support.
533 for more information.
536 returns the maximal number of queued connections, as set by
539 returns the number of unaccepted complete connections.
541 returns the number of unaccepted incomplete connections.
543 .Dv SO_MAX_PACING_RATE
544 instruct the socket and underlying network adapter layers to limit the
545 transfer rate to the given unsigned 32-bit value in bytes per second.
548 disables support for protocol offloads.
549 At present, this prevents TCP sockets from using TCP offload engines.
551 disables support for a specific TCP offload known as direct data
553 DDP is an offload supported by Chelsio network adapters that permits
554 reassembled TCP data streams to be received via zero-copy in
555 user-supplied buffers using
564 system calls succeed unless:
569 is not a valid descriptor.
573 is a file, not a socket.
574 .It Bq Er ENOPROTOOPT
575 The option is unknown at the level indicated.
577 The address pointed to by
579 is not in a valid part of the process address space.
582 this error may also be returned if
584 is not in a valid part of the process address space.
588 on a non-listening socket was attempted.
590 A memory allocation failed that was required to service the request.
595 system call may also return the following error:
598 Insufficient resources were available in the system
599 to perform the operation.
615 .Xr accept_filter 9 ,
622 system calls appeared in
625 Several of the socket options should be handled at lower levels of the system.