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32 .\" @(#)getsockopt.2 8.4 (Berkeley) 5/2/95
41 .Nd get and set options on sockets
48 .Fn getsockopt "int s" "int level" "int optname" "void *optval" "socklen_t *optlen"
50 .Fn setsockopt "int s" "int level" "int optname" "const void *optval" "socklen_t optlen"
57 associated with a socket. Options may exist at multiple
58 protocol levels; they are always present at the uppermost
62 When manipulating socket options the level at which the
63 option resides and the name of the option must be specified.
64 To manipulate options at the socket level,
68 To manipulate options at any
69 other level the protocol number of the appropriate protocol
70 controlling the option is supplied. For example,
71 to indicate that an option is to be interpreted by the
75 should be set to the protocol number of
84 are used to access option values for
88 they identify a buffer in which the value for the
89 requested option(s) are to be returned. For
92 is a value-result parameter, initially containing the
93 size of the buffer pointed to by
95 and modified on return to indicate the actual size of
96 the value returned. If no option value is
97 to be supplied or returned,
102 and any specified options are passed uninterpreted to the appropriate
103 protocol module for interpretation.
105 .Ao Pa sys/socket.h Ac
106 contains definitions for
107 socket level options, described below.
108 Options at other protocol levels vary in format and
109 name; consult the appropriate entries in
113 Most socket-level options utilize an
119 the parameter should be non-zero to enable a boolean option,
120 or zero if the option is to be disabled.
124 parameter, defined in
125 .Ao Pa sys/socket.h Ac ,
126 which specifies the desired state of the option and the
127 linger interval (see below).
133 parameter, defined in
134 .Ao Pa sys/time.h Ac .
136 The following options are recognized at the socket level.
137 Except as noted, each may be examined with
141 .Bl -column SO_ACCEPTFILTER -offset indent
142 .It Dv SO_DEBUG Ta "enables recording of debugging information"
143 .It Dv SO_REUSEADDR Ta "enables local address reuse"
144 .It Dv SO_REUSEPORT Ta "enables duplicate address and port bindings"
145 .It Dv SO_KEEPALIVE Ta "enables keep connections alive"
146 .It Dv SO_DONTROUTE Ta "enables routing bypass for outgoing messages"
147 .It Dv SO_LINGER Ta "linger on close if data present"
148 .It Dv SO_BROADCAST Ta "enables permission to transmit broadcast messages"
149 .It Dv SO_OOBINLINE Ta "enables reception of out-of-band data in band"
150 .It Dv SO_SNDBUF Ta "set buffer size for output"
151 .It Dv SO_RCVBUF Ta "set buffer size for input"
152 .It Dv SO_SNDLOWAT Ta "set minimum count for output"
153 .It Dv SO_RCVLOWAT Ta "set minimum count for input"
154 .It Dv SO_SNDTIMEO Ta "set timeout value for output"
155 .It Dv SO_RCVTIMEO Ta "set timeout value for input"
156 .It Dv SO_ACCEPTFILTER Ta "set accept filter on listen socket"
157 .It Dv SO_TYPE Ta "get the type of the socket (get only)"
158 .It Dv SO_ERROR Ta "get and clear error on the socket (get only)"
162 enables debugging in the underlying protocol modules.
164 indicates that the rules used in validating addresses supplied
167 call should allow reuse of local addresses.
169 allows completely duplicate bindings by multiple processes
172 before binding the port.
173 This option permits multiple instances of a program to each
174 receive UDP/IP multicast or broadcast datagrams destined for the bound port.
177 periodic transmission of messages on a connected socket. Should the
178 connected party fail to respond to these messages, the connection is
179 considered broken and processes using the socket are notified via a
181 signal when attempting to send data.
183 indicates that outgoing messages should
184 bypass the standard routing facilities. Instead, messages are directed
185 to the appropriate network interface according to the network portion
186 of the destination address.
189 controls the action taken when unsent messages
190 are queued on socket and a
193 If the socket promises reliable delivery of data and
196 the system will block the process on the
198 attempt until it is able to transmit the data or until it decides it
199 is unable to deliver the information (a timeout period, termed the
200 linger interval, is specified in seconds in the
209 is issued, the system will process the close in a manner that allows
210 the process to continue as quickly as possible.
214 requests permission to send broadcast datagrams
216 Broadcast was a privileged operation in earlier versions of the system.
217 With protocols that support out-of-band data, the
220 requests that out-of-band data be placed in the normal data input queue
221 as received; it will then be accessible with
228 Some protocols always behave as if this option is set.
232 are options to adjust the normal
233 buffer sizes allocated for output and input buffers, respectively.
234 The buffer size may be increased for high-volume connections,
235 or may be decreased to limit the possible backlog of incoming data.
236 The system places an absolute maximum on these values, which is accessible
240 .Dq Li kern.ipc.maxsockbuf .
243 is an option to set the minimum count for output operations.
244 Most output operations process all of the data supplied
245 by the call, delivering data to the protocol for transmission
246 and blocking as necessary for flow control.
247 Nonblocking output operations will process as much data as permitted
248 subject to flow control without blocking, but will process no data
249 if flow control does not allow the smaller of the low water mark value
250 or the entire request to be processed.
253 operation testing the ability to write to a socket will return true
254 only if the low water mark amount could be processed.
255 The default value for
257 is set to a convenient size for network efficiency, often 1024.
259 is an option to set the minimum count for input operations.
260 In general, receive calls will block until any (non-zero) amount of data
261 is received, then return with the smaller of the amount available or the amount
263 The default value for
268 is set to a larger value, blocking receive calls normally
269 wait until they have received the smaller of the low water mark value
270 or the requested amount.
271 Receive calls may still return less than the low water mark if an error
272 occurs, a signal is caught, or the type of data next in the receive queue
273 is different from that which was returned.
276 is an option to set a timeout value for output operations.
279 parameter with the number of seconds and microseconds
280 used to limit waits for output operations to complete.
281 If a send operation has blocked for this much time,
282 it returns with a partial count
285 if no data were sent.
286 In the current implementation, this timer is restarted each time additional
287 data are delivered to the protocol,
288 implying that the limit applies to output portions ranging in size
289 from the low water mark to the high water mark for output.
291 is an option to set a timeout value for input operations.
294 parameter with the number of seconds and microseconds
295 used to limit waits for input operations to complete.
296 In the current implementation, this timer is restarted each time additional
297 data are received by the protocol,
298 and thus the limit is in effect an inactivity timer.
299 If a receive operation has been blocked for this much time without
300 receiving additional data, it returns with a short count
303 if no data were received.
309 which will filter incoming connections
310 on a listening stream socket before being presented for
313 struct accept_filter_arg {
321 .Fa struct accept_filter_arg .
322 that will select and configure the
323 .Xr accept_filter 9 .
325 should be filled with the name of the accept filter
326 that the application wishes to place on the listening socket.
328 is an optional parameter that can be passed to the accept
331 to provide additional configuration options at attach time.
334 of NULL will remove the filter.
340 are options used only with
343 returns the type of the socket, such as
345 it is useful for servers that inherit sockets on startup.
347 returns any pending error on the socket and clears
349 It may be used to check for asynchronous errors on connected
350 datagram sockets or for other asynchronous errors.
351 .Sh IMPLEMENTATION NOTES
352 In the non-threaded library
354 is implemented as the
358 In the threaded library, the
360 syscall is assembled to
361 .Fn _thread_sys_getsockopt
364 is implemented as a function which locks
366 for read and write, then calls
367 .Fn _thread_sys_getsockopt .
373 In the non-threaded library
375 is implemented as the
379 In the threaded library, the
381 syscall is assembled to
382 .Fn _thread_sys_setsockopt
385 is implemented as a function which locks
387 for read and write, then calls
388 .Fn _thread_sys_setsockopt .
396 The call succeeds unless:
401 is not a valid descriptor.
405 is a file, not a socket.
406 .It Bq Er ENOPROTOOPT
407 The option is unknown at the level indicated.
409 The address pointed to by
411 is not in a valid part of the process address space.
414 this error may also be returned if
416 is not in a valid part of the process address space.
427 Several of the socket options should be handled at lower levels of the system.
431 system call appeared in