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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_PROTOCOL Ta "get the protocol number for the socket (get only)"
176 .It Dv SO_PROTOTYPE Ta "SunOS alias for the Linux SO_PROTOCOL (get only)"
177 .It Dv SO_ERROR Ta "get and clear error on the socket (get only)"
178 .It Dv SO_SETFIB Ta "set the associated FIB (routing table) for the socket (set only)"
181 The following options are recognized in
183 .Bl -column SO_LISTENINCQLEN -offset indent
184 .It Dv SO_LABEL Ta "get MAC label of the socket (get only)"
185 .It Dv SO_PEERLABEL Ta "get socket's peer's MAC label (get only)"
186 .It Dv SO_LISTENQLIMIT Ta "get backlog limit of the socket (get only)"
187 .It Dv SO_LISTENQLEN Ta "get complete queue length of the socket (get only)"
188 .It Dv SO_LISTENINCQLEN Ta "get incomplete queue length of the socket (get only)"
189 .It Dv SO_USER_COOKIE Ta "set the 'so_user_cookie' value for the socket (uint32_t, set only)"
193 enables debugging in the underlying protocol modules.
196 indicates that the rules used in validating addresses supplied
199 system call should allow reuse of local addresses.
202 allows completely duplicate bindings by multiple processes
205 before binding the port.
206 This option permits multiple instances of a program to each
207 receive UDP/IP multicast or broadcast datagrams destined for the bound port.
211 periodic transmission of messages on a connected socket.
213 connected party fail to respond to these messages, the connection is
214 considered broken and processes using the socket are notified via a
216 signal when attempting to send data.
219 indicates that outgoing messages should
220 bypass the standard routing facilities.
221 Instead, messages are directed
222 to the appropriate network interface according to the network portion
223 of the destination address.
226 controls the action taken when unsent messages
227 are queued on socket and a
230 If the socket promises reliable delivery of data and
233 the system will block the process on the
235 attempt until it is able to transmit the data or until it decides it
236 is unable to deliver the information (a timeout period, termed the
237 linger interval, is specified in seconds in the
246 is issued, the system will process the close in a manner that allows
247 the process to continue as quickly as possible.
251 requests permission to send broadcast datagrams
253 Broadcast was a privileged operation in earlier versions of the system.
255 With protocols that support out-of-band data, the
258 requests that out-of-band data be placed in the normal data input queue
259 as received; it will then be accessible with
266 Some protocols always behave as if this option is set.
271 are options to adjust the normal
272 buffer sizes allocated for output and input buffers, respectively.
273 The buffer size may be increased for high-volume connections,
274 or may be decreased to limit the possible backlog of incoming data.
275 The system places an absolute maximum on these values, which is accessible
279 .Dq Li kern.ipc.maxsockbuf .
282 is an option to set the minimum count for output operations.
283 Most output operations process all of the data supplied
284 by the call, delivering data to the protocol for transmission
285 and blocking as necessary for flow control.
286 Nonblocking output operations will process as much data as permitted
287 subject to flow control without blocking, but will process no data
288 if flow control does not allow the smaller of the low water mark value
289 or the entire request to be processed.
292 operation testing the ability to write to a socket will return true
293 only if the low water mark amount could be processed.
294 The default value for
296 is set to a convenient size for network efficiency, often 1024.
299 is an option to set the minimum count for input operations.
300 In general, receive calls will block until any (non-zero) amount of data
301 is received, then return with the smaller of the amount available or the amount
303 The default value for
308 is set to a larger value, blocking receive calls normally
309 wait until they have received the smaller of the low water mark value
310 or the requested amount.
311 Receive calls may still return less than the low water mark if an error
312 occurs, a signal is caught, or the type of data next in the receive queue
313 is different from that which was returned.
316 is an option to set a timeout value for output operations.
319 argument with the number of seconds and microseconds
320 used to limit waits for output operations to complete.
321 If a send operation has blocked for this much time,
322 it returns with a partial count
325 if no data were sent.
326 In the current implementation, this timer is restarted each time additional
327 data are delivered to the protocol,
328 implying that the limit applies to output portions ranging in size
329 from the low water mark to the high water mark for output.
332 is an option to set a timeout value for input operations.
335 argument with the number of seconds and microseconds
336 used to limit waits for input operations to complete.
337 In the current implementation, this timer is restarted each time additional
338 data are received by the protocol,
339 and thus the limit is in effect an inactivity timer.
340 If a receive operation has been blocked for this much time without
341 receiving additional data, it returns with a short count
344 if no data were received.
347 can be used to over-ride the default FIB (routing table) for the given socket.
348 The value must be from 0 to one less than the number returned from
353 can be used to set the uint32_t so_user_cookie field in the socket.
354 The value is an uint32_t, and can be used in the kernel code that
355 manipulates traffic related to the socket.
356 The default value for the field is 0.
357 As an example, the value can be used as the skipto target or
365 which will filter incoming connections
366 on a listening stream socket before being presented for
370 must be called on the socket before
371 trying to install the filter on it,
374 system call will fail.
376 struct accept_filter_arg {
386 .Fa struct accept_filter_arg
387 that will select and configure the
388 .Xr accept_filter 9 .
392 should be filled with the name of the accept filter
393 that the application wishes to place on the listening socket.
394 The optional argument
396 can be passed to the accept
399 to provide additional configuration options at attach time.
402 of NULL will remove the filter.
406 option controls generation of the
409 when writing to a connected socket where the other end has been
410 closed returns with the error
417 option is enabled on a
421 call will return a timestamp corresponding to when the datagram was received.
426 structure points to a buffer that contains a
428 structure followed by a
438 fields have the following values for TIMESTAMP:
440 cmsg_len = CMSG_LEN(sizeof(struct timeval));
441 cmsg_level = SOL_SOCKET;
442 cmsg_type = SCM_TIMESTAMP;
448 cmsg_len = CMSG_LEN(sizeof(struct bintime));
449 cmsg_level = SOL_SOCKET;
450 cmsg_type = SCM_BINTIME;
460 are options used only with
463 returns whether the socket is currently accepting connections,
464 that is, whether or not the
466 system call was invoked on the socket.
468 returns the type of the socket, such as
470 it is useful for servers that inherit sockets on startup.
472 returns the protocol number for the socket, for
478 returns any pending error on the socket and clears
480 It may be used to check for asynchronous errors on connected
481 datagram sockets or for other asynchronous errors.
485 returns the MAC label of the socket.
487 returns the MAC label of the socket's peer.
488 Note that your kernel must be compiled with MAC support.
491 for more information.
493 returns the maximal number of queued connections, as set by
496 returns the number of unaccepted complete connections.
498 returns the number of unaccepted incomplete connections.
502 The call succeeds unless:
507 is not a valid descriptor.
511 is a file, not a socket.
512 .It Bq Er ENOPROTOOPT
513 The option is unknown at the level indicated.
515 The address pointed to by
517 is not in a valid part of the process address space.
520 this error may also be returned if
522 is not in a valid part of the process address space.
526 on a non-listening socket was attempted.
542 .Xr accept_filter 9 ,
549 system calls appeared in
552 Several of the socket options should be handled at lower levels of the system.