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32 .\" @(#)getsockopt.2 8.4 (Berkeley) 5/2/95
41 .Nd get and set options on sockets
43 .Fd #include <sys/types.h>
44 .Fd #include <sys/socket.h>
46 .Fn getsockopt "int s" "int level" "int optname" "void *optval" "int *optlen"
48 .Fn setsockopt "int s" "int level" "int optname" "const void *optval" "int optlen"
55 associated with a socket. Options may exist at multiple
56 protocol levels; they are always present at the uppermost
60 When manipulating socket options the level at which the
61 option resides and the name of the option must be specified.
62 To manipulate options at the socket level,
66 To manipulate options at any
67 other level the protocol number of the appropriate protocol
68 controlling the option is supplied. For example,
69 to indicate that an option is to be interpreted by the
73 should be set to the protocol number of
82 are used to access option values for
86 they identify a buffer in which the value for the
87 requested option(s) are to be returned. For
90 is a value-result parameter, initially containing the
91 size of the buffer pointed to by
93 and modified on return to indicate the actual size of
94 the value returned. If no option value is
95 to be supplied or returned,
100 and any specified options are passed uninterpreted to the appropriate
101 protocol module for interpretation.
103 .Ao Pa sys/socket.h Ac
104 contains definitions for
105 socket level options, described below.
106 Options at other protocol levels vary in format and
107 name; consult the appropriate entries in
111 Most socket-level options utilize an
117 the parameter should be non-zero to enable a boolean option,
118 or zero if the option is to be disabled.
122 parameter, defined in
123 .Ao Pa sys/socket.h Ac ,
124 which specifies the desired state of the option and the
125 linger interval (see below).
131 parameter, defined in
132 .Ao Pa sys/time.h Ac .
134 The following options are recognized at the socket level.
135 Except as noted, each may be examined with
139 .Bl -column SO_OOBINLINE -offset indent
140 .It Dv SO_DEBUG Ta "enables recording of debugging information"
141 .It Dv SO_REUSEADDR Ta "enables local address reuse"
142 .It Dv SO_REUSEPORT Ta "enables duplicate address and port bindings"
143 .It Dv SO_KEEPALIVE Ta "enables keep connections alive"
144 .It Dv SO_DONTROUTE Ta "enables routing bypass for outgoing messages"
145 .It Dv SO_LINGER Ta "linger on close if data present"
146 .It Dv SO_BROADCAST Ta "enables permission to transmit broadcast messages"
147 .It Dv SO_OOBINLINE Ta "enables reception of out-of-band data in band"
148 .It Dv SO_SNDBUF Ta "set buffer size for output"
149 .It Dv SO_RCVBUF Ta "set buffer size for input"
150 .It Dv SO_SNDLOWAT Ta "set minimum count for output"
151 .It Dv SO_RCVLOWAT Ta "set minimum count for input"
152 .It Dv SO_SNDTIMEO Ta "set timeout value for output"
153 .It Dv SO_RCVTIMEO Ta "set timeout value for input"
154 .It Dv SO_TYPE Ta "get the type of the socket (get only)"
155 .It Dv SO_ERROR Ta "get and clear error on the socket (get only)"
159 enables debugging in the underlying protocol modules.
161 indicates that the rules used in validating addresses supplied
164 call should allow reuse of local addresses.
166 allows completely duplicate bindings by multiple processes
169 before binding the port.
170 This option permits multiple instances of a program to each
171 receive UDP/IP multicast or broadcast datagrams destined for the bound port.
174 periodic transmission of messages on a connected socket. Should the
175 connected party fail to respond to these messages, the connection is
176 considered broken and processes using the socket are notified via a
178 signal when attempting to send data.
180 indicates that outgoing messages should
181 bypass the standard routing facilities. Instead, messages are directed
182 to the appropriate network interface according to the network portion
183 of the destination address.
186 controls the action taken when unsent messages
187 are queued on socket and a
190 If the socket promises reliable delivery of data and
191 .Dv SO_LINGER is set,
192 the system will block the process on the
194 attempt until it is able to transmit the data or until it decides it
195 is unable to deliver the information (a timeout period, termed the
196 linger interval, is specified in seconds in the
205 is issued, the system will process the close in a manner that allows
206 the process to continue as quickly as possible.
210 requests permission to send broadcast datagrams
212 Broadcast was a privileged operation in earlier versions of the system.
213 With protocols that support out-of-band data, the
216 requests that out-of-band data be placed in the normal data input queue
217 as received; it will then be accessible with
224 Some protocols always behave as if this option is set.
228 are options to adjust the normal
229 buffer sizes allocated for output and input buffers, respectively.
230 The buffer size may be increased for high-volume connections,
231 or may be decreased to limit the possible backlog of incoming data.
232 The system places an absolute maximum on these values, which is accessible
236 .Dq Li kern.ipc.maxsockbuf .
239 is an option to set the minimum count for output operations.
240 Most output operations process all of the data supplied
241 by the call, delivering data to the protocol for transmission
242 and blocking as necessary for flow control.
243 Nonblocking output operations will process as much data as permitted
244 subject to flow control without blocking, but will process no data
245 if flow control does not allow the smaller of the low water mark value
246 or the entire request to be processed.
249 operation testing the ability to write to a socket will return true
250 only if the low water mark amount could be processed.
251 The default value for
253 is set to a convenient size for network efficiency, often 1024.
255 is an option to set the minimum count for input operations.
256 In general, receive calls will block until any (non-zero) amount of data
257 is received, then return with the smaller of the amount available or the amount
259 The default value for
264 is set to a larger value, blocking receive calls normally
265 wait until they have received the smaller of the low water mark value
266 or the requested amount.
267 Receive calls may still return less than the low water mark if an error
268 occurs, a signal is caught, or the type of data next in the receive queue
269 is different from that which was returned.
272 is an option to set a timeout value for output operations.
275 parameter with the number of seconds and microseconds
276 used to limit waits for output operations to complete.
277 If a send operation has blocked for this much time,
278 it returns with a partial count
281 if no data were sent.
282 In the current implementation, this timer is restarted each time additional
283 data are delivered to the protocol,
284 implying that the limit applies to output portions ranging in size
285 from the low water mark to the high water mark for output.
287 is an option to set a timeout value for input operations.
290 parameter with the number of seconds and microseconds
291 used to limit waits for input operations to complete.
292 In the current implementation, this timer is restarted each time additional
293 data are received by the protocol,
294 and thus the limit is in effect an inactivity timer.
295 If a receive operation has been blocked for this much time without
296 receiving additional data, it returns with a short count
299 if no data were received.
305 are options used only with
308 returns the type of the socket, such as
310 it is useful for servers that inherit sockets on startup.
312 returns any pending error on the socket and clears
314 It may be used to check for asynchronous errors on connected
315 datagram sockets or for other asynchronous errors.
316 .Sh IMPLEMENTATION NOTES
318 In the non-threaded library
320 is implemented as the
324 In the threaded library, the
326 syscall is assembled to
327 .Fn _thread_sys_getsockopt
330 is implemented as a function which locks
332 for read and write, then calls
333 .Fn _thread_sys_getsockopt .
339 In the non-threaded library
341 is implemented as the
345 In the threaded library, the
347 syscall is assembled to
348 .Fn _thread_sys_setsockopt
351 is implemented as a function which locks
353 for read and write, then calls
354 .Fn _thread_sys_setsockopt .
360 A 0 is returned if the call succeeds, -1 if it fails.
362 The call succeeds unless:
363 .Bl -tag -width ENOPROTOOPTAA
367 is not a valid descriptor.
371 is a file, not a socket.
372 .It Bq Er ENOPROTOOPT
373 The option is unknown at the level indicated.
375 The address pointed to by
377 is not in a valid part of the process address space.
380 this error may also be returned if
382 is not in a valid part of the process address space.
392 Several of the socket options should be handled at lower levels of the system.
396 system call appeared in