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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_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"
194 .It Dv SO_NO_OFFLOAD Ta "disables protocol offloads"
195 .It Dv SO_NO_DDP Ta "disables direct data placement offload"
199 enables debugging in the underlying protocol modules.
202 indicates that the rules used in validating addresses supplied
205 system call should allow reuse of local addresses.
208 allows completely duplicate bindings by multiple processes
211 before binding the port.
212 This option permits multiple instances of a program to each
213 receive UDP/IP multicast or broadcast datagrams destined for the bound port.
216 allows completely duplicate bindings by multiple processes
219 before binding the port.
220 Incoming TCP and UDP connections are distributed among the sharing
221 processes based on a hash function of local port number, foreign IP
222 address and port number.
223 A maximum of 256 processes can share one socket.
227 periodic transmission of messages on a connected socket.
229 connected party fail to respond to these messages, the connection is
230 considered broken and processes using the socket are notified via a
232 signal when attempting to send data.
235 indicates that outgoing messages should
236 bypass the standard routing facilities.
237 Instead, messages are directed
238 to the appropriate network interface according to the network portion
239 of the destination address.
242 controls the action taken when unsent messages
243 are queued on socket and a
246 If the socket promises reliable delivery of data and
249 the system will block the process on the
251 attempt until it is able to transmit the data or until it decides it
252 is unable to deliver the information (a timeout period, termed the
253 linger interval, is specified in seconds in the
262 is issued, the system will process the close in a manner that allows
263 the process to continue as quickly as possible.
267 requests permission to send broadcast datagrams
269 Broadcast was a privileged operation in earlier versions of the system.
271 With protocols that support out-of-band data, the
274 requests that out-of-band data be placed in the normal data input queue
275 as received; it will then be accessible with
282 Some protocols always behave as if this option is set.
287 are options to adjust the normal
288 buffer sizes allocated for output and input buffers, respectively.
289 The buffer size may be increased for high-volume connections,
290 or may be decreased to limit the possible backlog of incoming data.
291 The system places an absolute maximum on these values, which is accessible
295 .Dq Li kern.ipc.maxsockbuf .
298 is an option to set the minimum count for output operations.
299 Most output operations process all of the data supplied
300 by the call, delivering data to the protocol for transmission
301 and blocking as necessary for flow control.
302 Nonblocking output operations will process as much data as permitted
303 subject to flow control without blocking, but will process no data
304 if flow control does not allow the smaller of the low water mark value
305 or the entire request to be processed.
308 operation testing the ability to write to a socket will return true
309 only if the low water mark amount could be processed.
310 The default value for
312 is set to a convenient size for network efficiency, often 1024.
315 is an option to set the minimum count for input operations.
316 In general, receive calls will block until any (non-zero) amount of data
317 is received, then return with the smaller of the amount available or the amount
319 The default value for
324 is set to a larger value, blocking receive calls normally
325 wait until they have received the smaller of the low water mark value
326 or the requested amount.
327 Receive calls may still return less than the low water mark if an error
328 occurs, a signal is caught, or the type of data next in the receive queue
329 is different from that which was returned.
332 is an option to set a timeout value for output operations.
335 argument with the number of seconds and microseconds
336 used to limit waits for output operations to complete.
337 If a send operation has blocked for this much time,
338 it returns with a partial count
341 if no data were sent.
342 In the current implementation, this timer is restarted each time additional
343 data are delivered to the protocol,
344 implying that the limit applies to output portions ranging in size
345 from the low water mark to the high water mark for output.
348 is an option to set a timeout value for input operations.
351 argument with the number of seconds and microseconds
352 used to limit waits for input operations to complete.
353 In the current implementation, this timer is restarted each time additional
354 data are received by the protocol,
355 and thus the limit is in effect an inactivity timer.
356 If a receive operation has been blocked for this much time without
357 receiving additional data, it returns with a short count
360 if no data were received.
363 can be used to over-ride the default FIB (routing table) for the given socket.
364 The value must be from 0 to one less than the number returned from
369 can be used to set the uint32_t so_user_cookie field in the socket.
370 The value is an uint32_t, and can be used in the kernel code that
371 manipulates traffic related to the socket.
372 The default value for the field is 0.
373 As an example, the value can be used as the skipto target or
381 which will filter incoming connections
382 on a listening stream socket before being presented for
386 must be called on the socket before
387 trying to install the filter on it,
390 system call will fail.
392 struct accept_filter_arg {
402 .Fa struct accept_filter_arg
403 that will select and configure the
404 .Xr accept_filter 9 .
408 should be filled with the name of the accept filter
409 that the application wishes to place on the listening socket.
410 The optional argument
412 can be passed to the accept
415 to provide additional configuration options at attach time.
418 of NULL will remove the filter.
422 option controls generation of the
425 when writing to a connected socket where the other end has been
426 closed returns with the error
433 option is enabled on a
437 call may return a timestamp corresponding to when the datagram was received.
438 However, it may not, for example due to a resource shortage.
443 structure points to a buffer that contains a
445 structure followed by a
455 fields have the following values for TIMESTAMP by default:
457 cmsg_len = CMSG_LEN(sizeof(struct timeval));
458 cmsg_level = SOL_SOCKET;
459 cmsg_type = SCM_TIMESTAMP;
465 cmsg_len = CMSG_LEN(sizeof(struct bintime));
466 cmsg_level = SOL_SOCKET;
467 cmsg_type = SCM_BINTIME;
470 Additional timestamp types are available by following
474 which requests a specific timestamp format to be returned instead of
475 .Dv SCM_TIMESTAMP when
476 .Dv SO_TIMESTAMP is enabled.
479 values are recognized in
481 .Bl -column SO_TS_CLOCK -offset indent
482 .It Dv SO_TS_REALTIME_MICRO Ta "realtime (SCM_TIMESTAMP, struct timeval), default"
483 .It Dv SO_TS_BINTIME Ta "realtime (SCM_BINTIME, struct bintime)"
484 .It Dv SO_TS_REALTIME Ta "realtime (SCM_REALTIME, struct timespec)"
485 .It Dv SO_TS_MONOTONIC Ta "monotonic time (SCM_MONOTONIC, struct timespec)"
495 are options used only with
498 returns whether the socket is currently accepting connections,
499 that is, whether or not the
501 system call was invoked on the socket.
503 returns the type of the socket, such as
505 it is useful for servers that inherit sockets on startup.
507 returns the protocol number for the socket, for
513 returns any pending error on the socket and clears
515 It may be used to check for asynchronous errors on connected
516 datagram sockets or for other asynchronous errors.
519 returns the MAC label of the socket.
521 returns the MAC label of the socket's peer.
522 Note that your kernel must be compiled with MAC support.
525 for more information.
528 returns the maximal number of queued connections, as set by
531 returns the number of unaccepted complete connections.
533 returns the number of unaccepted incomplete connections.
535 .Dv SO_MAX_PACING_RATE
536 instruct the socket and underlying network adapter layers to limit the
537 transfer rate to the given unsigned 32-bit value in bytes per second.
540 disables support for protocol offloads.
541 At present, this prevents TCP sockets from using TCP offload engines.
543 disables support for a specific TCP offload known as direct data
545 DDP is an offload supported by Chelsio network adapters that permits
546 reassembled TCP data streams to be received via zero-copy in
547 user-supplied buffers using
556 system calls succeed unless:
561 is not a valid descriptor.
565 is a file, not a socket.
566 .It Bq Er ENOPROTOOPT
567 The option is unknown at the level indicated.
569 The address pointed to by
571 is not in a valid part of the process address space.
574 this error may also be returned if
576 is not in a valid part of the process address space.
580 on a non-listening socket was attempted.
582 A memory allocation failed that was required to service the request.
587 system call may also return the following error:
590 Insufficient resources were available in the system
591 to perform the operation.
607 .Xr accept_filter 9 ,
614 system calls appeared in
617 Several of the socket options should be handled at lower levels of the system.