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Neither the name of the University nor the names of its contributors 13.\" may be used to endorse or promote products derived from this software 14.\" without specific prior written permission. 15.\" 16.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 17.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 20.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26.\" SUCH DAMAGE. 27.\" 28.\" @(#)getsockopt.2 8.4 (Berkeley) 5/2/95 29.\" $FreeBSD: src/lib/libc/sys/getsockopt.2,v 1.12.2.11 2002/01/09 17:44:15 yar Exp $ 30.\" $DragonFly: src/lib/libc/sys/getsockopt.2,v 1.5 2007/07/14 21:48:15 swildner Exp $ 31.\" 32.Dd May 2, 1995 33.Dt GETSOCKOPT 2 34.Os 35.Sh NAME 36.Nm getsockopt , 37.Nm setsockopt 38.Nd get and set options on sockets 39.Sh LIBRARY 40.Lb libc 41.Sh SYNOPSIS 42.In sys/types.h 43.In sys/socket.h 44.Ft int 45.Fn getsockopt "int s" "int level" "int optname" "void *optval" "socklen_t *optlen" 46.Ft int 47.Fn setsockopt "int s" "int level" "int optname" "const void *optval" "socklen_t optlen" 48.Sh DESCRIPTION 49.Fn Getsockopt 50and 51.Fn setsockopt 52manipulate the 53.Em options 54associated with a socket. Options may exist at multiple 55protocol levels; they are always present at the uppermost 56.Dq socket 57level. 58.Pp 59When manipulating socket options the level at which the 60option resides and the name of the option must be specified. 61To manipulate options at the socket level, 62.Fa level 63is specified as 64.Dv SOL_SOCKET . 65To manipulate options at any 66other level the protocol number of the appropriate protocol 67controlling the option is supplied. For example, 68to indicate that an option is to be interpreted by the 69.Tn TCP 70protocol, 71.Fa level 72should be set to the protocol number of 73.Tn TCP ; 74see 75.Xr getprotoent 3 . 76.Pp 77The parameters 78.Fa optval 79and 80.Fa optlen 81are used to access option values for 82.Fn setsockopt . 83For 84.Fn getsockopt 85they identify a buffer in which the value for the 86requested option(s) are to be returned. For 87.Fn getsockopt , 88.Fa optlen 89is a value-result parameter, initially containing the 90size of the buffer pointed to by 91.Fa optval , 92and modified on return to indicate the actual size of 93the value returned. If no option value is 94to be supplied or returned, 95.Fa optval 96may be NULL. 97.Pp 98.Fa Optname 99and any specified options are passed uninterpreted to the appropriate 100protocol module for interpretation. 101The include file 102.In sys/socket.h 103contains definitions for 104socket level options, described below. 105Options at other protocol levels vary in format and 106name; consult the appropriate entries in 107section 1084 of the manual. 109.Pp 110Most socket-level options utilize an 111.Fa int 112parameter for 113.Fa optval . 114For 115.Fn setsockopt , 116the parameter should be non-zero to enable a boolean option, 117or zero if the option is to be disabled. 118.Dv SO_LINGER 119uses a 120.Fa struct linger 121parameter, defined in 122.In sys/socket.h , 123which specifies the desired state of the option and the 124linger interval (see below). 125.Dv SO_SNDTIMEO 126and 127.Dv SO_RCVTIMEO 128use a 129.Fa struct timeval 130parameter, defined in 131.In sys/time.h . 132.Pp 133The following options are recognized at the socket level. 134Except as noted, each may be examined with 135.Fn getsockopt 136and set with 137.Fn setsockopt . 138.Bl -column SO_ACCEPTFILTER -offset indent 139.It Dv SO_DEBUG Ta "enables recording of debugging information" 140.It Dv SO_REUSEADDR Ta "enables local address reuse" 141.It Dv SO_REUSEPORT Ta "enables duplicate address and port bindings" 142.It Dv SO_KEEPALIVE Ta "enables keep connections alive" 143.It Dv SO_DONTROUTE Ta "enables routing bypass for outgoing messages" 144.It Dv SO_LINGER Ta "linger on close if data present" 145.It Dv SO_BROADCAST Ta "enables permission to transmit broadcast messages" 146.It Dv SO_OOBINLINE Ta "enables reception of out-of-band data in band" 147.It Dv SO_SNDBUF Ta "set buffer size for output" 148.It Dv SO_RCVBUF Ta "set buffer size for input" 149.It Dv SO_SNDLOWAT Ta "set minimum count for output" 150.It Dv SO_RCVLOWAT Ta "set minimum count for input" 151.It Dv SO_SNDTIMEO Ta "set timeout value for output" 152.It Dv SO_RCVTIMEO Ta "set timeout value for input" 153.It Dv SO_ACCEPTFILTER Ta "set accept filter on listening socket" 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)" 156.El 157.Pp 158.Dv SO_DEBUG 159enables debugging in the underlying protocol modules. 160.Dv SO_REUSEADDR 161indicates that the rules used in validating addresses supplied 162in a 163.Xr bind 2 164call should allow reuse of local addresses. 165.Dv SO_REUSEPORT 166allows completely duplicate bindings by multiple processes 167if they all set 168.Dv SO_REUSEPORT 169before binding the port. 170This option permits multiple instances of a program to each 171receive UDP/IP multicast or broadcast datagrams destined for the bound port. 172.Dv SO_KEEPALIVE 173enables the 174periodic transmission of messages on a connected socket. Should the 175connected party fail to respond to these messages, the connection is 176considered broken and processes using the socket are notified via a 177.Dv SIGPIPE 178signal when attempting to send data. 179.Dv SO_DONTROUTE 180indicates that outgoing messages should 181bypass the standard routing facilities. Instead, messages are directed 182to the appropriate network interface according to the network portion 183of the destination address. 184.Pp 185.Dv SO_LINGER 186controls the action taken when unsent messages 187are queued on socket and a 188.Xr close 2 189is performed. 190If the socket promises reliable delivery of data and 191.Dv SO_LINGER 192is set, 193the system will block the process on the 194.Xr close 2 195attempt until it is able to transmit the data or until it decides it 196is unable to deliver the information (a timeout period, termed the 197linger interval, is specified in seconds in the 198.Fn setsockopt 199call when 200.Dv SO_LINGER 201is requested). 202If 203.Dv SO_LINGER 204is disabled and a 205.Xr close 2 206is issued, the system will process the close in a manner that allows 207the process to continue as quickly as possible. 208.Pp 209The option 210.Dv SO_BROADCAST 211requests permission to send broadcast datagrams 212on the socket. 213Broadcast was a privileged operation in earlier versions of the system. 214With protocols that support out-of-band data, the 215.Dv SO_OOBINLINE 216option 217requests that out-of-band data be placed in the normal data input queue 218as received; it will then be accessible with 219.Xr recv 2 220or 221.Xr read 2 222calls without the 223.Dv MSG_OOB 224flag. 225Some protocols always behave as if this option is set. 226.Dv SO_SNDBUF 227and 228.Dv SO_RCVBUF 229are options to adjust the normal 230buffer sizes allocated for output and input buffers, respectively. 231The buffer size may be increased for high-volume connections, 232or may be decreased to limit the possible backlog of incoming data. 233The system places an absolute maximum on these values, which is accessible 234through the 235.Xr sysctl 3 236MIB variable 237.Va kern.ipc.maxsockbuf . 238.Pp 239.Dv SO_SNDLOWAT 240is an option to set the minimum count for output operations. 241Most output operations process all of the data supplied 242by the call, delivering data to the protocol for transmission 243and blocking as necessary for flow control. 244Nonblocking output operations will process as much data as permitted 245subject to flow control without blocking, but will process no data 246if flow control does not allow the smaller of the low water mark value 247or the entire request to be processed. 248A 249.Xr select 2 250operation testing the ability to write to a socket will return true 251only if the low water mark amount could be processed. 252The default value for 253.Dv SO_SNDLOWAT 254is set to a convenient size for network efficiency, often 1024. 255.Dv SO_RCVLOWAT 256is an option to set the minimum count for input operations. 257In general, receive calls will block until any (non-zero) amount of data 258is received, then return with the smaller of the amount available or the amount 259requested. 260The default value for 261.Dv SO_RCVLOWAT 262is 1. 263If 264.Dv SO_RCVLOWAT 265is set to a larger value, blocking receive calls normally 266wait until they have received the smaller of the low water mark value 267or the requested amount. 268Receive calls may still return less than the low water mark if an error 269occurs, a signal is caught, or the type of data next in the receive queue 270is different from that which was returned. 271.Pp 272.Dv SO_SNDTIMEO 273is an option to set a timeout value for output operations. 274It accepts a 275.Fa struct timeval 276parameter with the number of seconds and microseconds 277used to limit waits for output operations to complete. 278If a send operation has blocked for this much time, 279it returns with a partial count 280or with the error 281.Er EWOULDBLOCK 282if no data were sent. 283In the current implementation, this timer is restarted each time additional 284data are delivered to the protocol, 285implying that the limit applies to output portions ranging in size 286from the low water mark to the high water mark for output. 287.Dv SO_RCVTIMEO 288is an option to set a timeout value for input operations. 289It accepts a 290.Fa struct timeval 291parameter with the number of seconds and microseconds 292used to limit waits for input operations to complete. 293In the current implementation, this timer is restarted each time additional 294data are received by the protocol, 295and thus the limit is in effect an inactivity timer. 296If a receive operation has been blocked for this much time without 297receiving additional data, it returns with a short count 298or with the error 299.Er EWOULDBLOCK 300if no data were received. 301.Pp 302.Dv SO_ACCEPTFILTER 303places an 304.Xr accept_filter 9 305on the socket, 306which will filter incoming connections 307on a listening stream socket before being presented for 308.Xr accept 2 . 309Once more, 310.Xr listen 2 311must be called on the socket before 312trying to install the filter on it, 313or else the 314.Fn setsockopt 315call will fail. 316.Bd -literal 317struct accept_filter_arg { 318 char af_name[16]; 319 char af_arg[256-16]; 320}; 321.Ed 322.Pp 323.Fa optval 324should point to a 325.Fa struct accept_filter_arg 326that will select and configure the 327.Xr accept_filter 9 . 328.Fa af_name 329should be filled with the name of the accept filter 330that the application wishes to place on the listening socket. 331.Fa af_arg 332is an optional parameter that can be passed to the accept 333filter specified by 334.Fa af_name 335to provide additional configuration options at attach time. 336Passing in an 337.Fa optval 338of NULL will remove the filter. 339.Pp 340Finally, 341.Dv SO_TYPE 342and 343.Dv SO_ERROR 344are options used only with 345.Fn getsockopt . 346.Dv SO_TYPE 347returns the type of the socket, such as 348.Dv SOCK_STREAM ; 349it is useful for servers that inherit sockets on startup. 350.Dv SO_ERROR 351returns any pending error on the socket and clears 352the error status. 353It may be used to check for asynchronous errors on connected 354datagram sockets or for other asynchronous errors. 355.Sh RETURN VALUES 356.Rv -std 357.Sh ERRORS 358The call succeeds unless: 359.Bl -tag -width Er 360.It Bq Er EBADF 361The argument 362.Fa s 363is not a valid descriptor. 364.It Bq Er ENOTSOCK 365The argument 366.Fa s 367is a file, not a socket. 368.It Bq Er ENOPROTOOPT 369The option is unknown at the level indicated. 370.It Bq Er EFAULT 371The address pointed to by 372.Fa optval 373is not in a valid part of the process address space. 374For 375.Fn getsockopt , 376this error may also be returned if 377.Fa optlen 378is not in a valid part of the process address space. 379.It Bq Er EINVAL 380Installing an 381.Xr accept_filter 9 382on a non-listening socket was attempted. 383.El 384.Sh SEE ALSO 385.Xr ioctl 2 , 386.Xr socket 2 , 387.Xr getprotoent 3 , 388.Xr sysctl 3 , 389.Xr protocols 5 , 390.Xr sysctl 8 , 391.Xr accept_filter 9 392.Sh HISTORY 393The 394.Fn getsockopt 395system call appeared in 396.Bx 4.2 . 397.Sh BUGS 398Several of the socket options should be handled at lower levels of the system. 399