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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_TYPE Ta "get the type of the socket (get only)"
176 .It Dv SO_PROTOCOL Ta "get the protocol number for the socket (get only)"
177 .It Dv SO_PROTOTYPE Ta "SunOS alias for the Linux SO_PROTOCOL (get only)"
178 .It Dv SO_ERROR Ta "get and clear error on the socket (get only)"
179 .It Dv SO_SETFIB Ta "set the associated FIB (routing table) for the socket (set only)"
182 The following options are recognized in
184 .Bl -column SO_LISTENINCQLEN -offset indent
185 .It Dv SO_LABEL Ta "get MAC label of the socket (get only)"
186 .It Dv SO_PEERLABEL Ta "get socket's peer's MAC label (get only)"
187 .It Dv SO_LISTENQLIMIT Ta "get backlog limit of the socket (get only)"
188 .It Dv SO_LISTENQLEN Ta "get complete queue length of the socket (get only)"
189 .It Dv SO_LISTENINCQLEN Ta "get incomplete queue length of the socket (get only)"
190 .It Dv SO_USER_COOKIE Ta "set the 'so_user_cookie' value for the socket (uint32_t, set only)"
191 .It Dv SO_TS_CLOCK Ta "set specific format of timestamp returned by SO_TIMESTAMP"
192 .It Dv SO_MAX_PACING_RATE Ta "set the maximum transmit rate in bytes per second for the socket"
196 enables debugging in the underlying protocol modules.
199 indicates that the rules used in validating addresses supplied
202 system call should allow reuse of local addresses.
205 allows completely duplicate bindings by multiple processes
208 before binding the port.
209 This option permits multiple instances of a program to each
210 receive UDP/IP multicast or broadcast datagrams destined for the bound port.
213 allows completely duplicate bindings by multiple processes
216 before binding the port.
217 Incoming TCP and UDP connections are distributed among the sharing
218 processes based on a hash function of local port number, foreign IP
219 address and port number. A maximum of 256 processes can share one socket.
223 periodic transmission of messages on a connected socket.
225 connected party fail to respond to these messages, the connection is
226 considered broken and processes using the socket are notified via a
228 signal when attempting to send data.
231 indicates that outgoing messages should
232 bypass the standard routing facilities.
233 Instead, messages are directed
234 to the appropriate network interface according to the network portion
235 of the destination address.
238 controls the action taken when unsent messages
239 are queued on socket and a
242 If the socket promises reliable delivery of data and
245 the system will block the process on the
247 attempt until it is able to transmit the data or until it decides it
248 is unable to deliver the information (a timeout period, termed the
249 linger interval, is specified in seconds in the
258 is issued, the system will process the close in a manner that allows
259 the process to continue as quickly as possible.
263 requests permission to send broadcast datagrams
265 Broadcast was a privileged operation in earlier versions of the system.
267 With protocols that support out-of-band data, the
270 requests that out-of-band data be placed in the normal data input queue
271 as received; it will then be accessible with
278 Some protocols always behave as if this option is set.
283 are options to adjust the normal
284 buffer sizes allocated for output and input buffers, respectively.
285 The buffer size may be increased for high-volume connections,
286 or may be decreased to limit the possible backlog of incoming data.
287 The system places an absolute maximum on these values, which is accessible
291 .Dq Li kern.ipc.maxsockbuf .
294 is an option to set the minimum count for output operations.
295 Most output operations process all of the data supplied
296 by the call, delivering data to the protocol for transmission
297 and blocking as necessary for flow control.
298 Nonblocking output operations will process as much data as permitted
299 subject to flow control without blocking, but will process no data
300 if flow control does not allow the smaller of the low water mark value
301 or the entire request to be processed.
304 operation testing the ability to write to a socket will return true
305 only if the low water mark amount could be processed.
306 The default value for
308 is set to a convenient size for network efficiency, often 1024.
311 is an option to set the minimum count for input operations.
312 In general, receive calls will block until any (non-zero) amount of data
313 is received, then return with the smaller of the amount available or the amount
315 The default value for
320 is set to a larger value, blocking receive calls normally
321 wait until they have received the smaller of the low water mark value
322 or the requested amount.
323 Receive calls may still return less than the low water mark if an error
324 occurs, a signal is caught, or the type of data next in the receive queue
325 is different from that which was returned.
328 is an option to set a timeout value for output operations.
331 argument with the number of seconds and microseconds
332 used to limit waits for output operations to complete.
333 If a send operation has blocked for this much time,
334 it returns with a partial count
337 if no data were sent.
338 In the current implementation, this timer is restarted each time additional
339 data are delivered to the protocol,
340 implying that the limit applies to output portions ranging in size
341 from the low water mark to the high water mark for output.
344 is an option to set a timeout value for input operations.
347 argument with the number of seconds and microseconds
348 used to limit waits for input operations to complete.
349 In the current implementation, this timer is restarted each time additional
350 data are received by the protocol,
351 and thus the limit is in effect an inactivity timer.
352 If a receive operation has been blocked for this much time without
353 receiving additional data, it returns with a short count
356 if no data were received.
359 can be used to over-ride the default FIB (routing table) for the given socket.
360 The value must be from 0 to one less than the number returned from
365 can be used to set the uint32_t so_user_cookie field in the socket.
366 The value is an uint32_t, and can be used in the kernel code that
367 manipulates traffic related to the socket.
368 The default value for the field is 0.
369 As an example, the value can be used as the skipto target or
377 which will filter incoming connections
378 on a listening stream socket before being presented for
382 must be called on the socket before
383 trying to install the filter on it,
386 system call will fail.
388 struct accept_filter_arg {
398 .Fa struct accept_filter_arg
399 that will select and configure the
400 .Xr accept_filter 9 .
404 should be filled with the name of the accept filter
405 that the application wishes to place on the listening socket.
406 The optional argument
408 can be passed to the accept
411 to provide additional configuration options at attach time.
414 of NULL will remove the filter.
418 option controls generation of the
421 when writing to a connected socket where the other end has been
422 closed returns with the error
429 option is enabled on a
433 call will return a timestamp corresponding to when the datagram was received.
438 structure points to a buffer that contains a
440 structure followed by a
450 fields have the following values for TIMESTAMP by default:
452 cmsg_len = CMSG_LEN(sizeof(struct timeval));
453 cmsg_level = SOL_SOCKET;
454 cmsg_type = SCM_TIMESTAMP;
460 cmsg_len = CMSG_LEN(sizeof(struct bintime));
461 cmsg_level = SOL_SOCKET;
462 cmsg_type = SCM_BINTIME;
465 Additional timestamp types are available by following
469 which requests a specific timestamp format to be returned instead of
470 .Dv SCM_TIMESTAMP when
471 .Dv SO_TIMESTAMP is enabled.
474 values are recognized in
476 .Bl -column SO_TS_CLOCK -offset indent
477 .It Dv SO_TS_REALTIME_MICRO Ta "realtime (SCM_TIMESTAMP, struct timeval), default"
478 .It Dv SO_TS_BINTIME Ta "realtime (SCM_BINTIME, struct bintime)"
479 .It Dv SO_TS_REALTIME Ta "realtime (SCM_REALTIME, struct timespec)"
480 .It Dv SO_TS_MONOTONIC Ta "monotonic time (SCM_MONOTONIC, struct timespec)"
490 are options used only with
493 returns whether the socket is currently accepting connections,
494 that is, whether or not the
496 system call was invoked on the socket.
498 returns the type of the socket, such as
500 it is useful for servers that inherit sockets on startup.
502 returns the protocol number for the socket, for
508 returns any pending error on the socket and clears
510 It may be used to check for asynchronous errors on connected
511 datagram sockets or for other asynchronous errors.
515 returns the MAC label of the socket.
517 returns the MAC label of the socket's peer.
518 Note that your kernel must be compiled with MAC support.
521 for more information.
523 returns the maximal number of queued connections, as set by
526 returns the number of unaccepted complete connections.
528 returns the number of unaccepted incomplete connections.
530 .Dv SO_MAX_PACING_RATE
531 instruct the socket and underlying network adapter layers to limit the
532 transfer rate to the given unsigned 32-bit value in bytes per second.
536 The call succeeds unless:
541 is not a valid descriptor.
545 is a file, not a socket.
546 .It Bq Er ENOPROTOOPT
547 The option is unknown at the level indicated.
549 The address pointed to by
551 is not in a valid part of the process address space.
554 this error may also be returned if
556 is not in a valid part of the process address space.
560 on a non-listening socket was attempted.
562 A memory allocation failed that was required to service the request.
578 .Xr accept_filter 9 ,
585 system calls appeared in
588 Several of the socket options should be handled at lower levels of the system.