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Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" @(#)getsockopt.2 8.4 (Berkeley) 5/2/95 33.\" $FreeBSD: src/lib/libc/sys/getsockopt.2,v 1.12.2.11 2002/01/09 17:44:15 yar Exp $ 34.\" $DragonFly: src/lib/libc/sys/getsockopt.2,v 1.5 2007/07/14 21:48:15 swildner Exp $ 35.\" 36.Dd May 2, 1995 37.Dt GETSOCKOPT 2 38.Os 39.Sh NAME 40.Nm getsockopt , 41.Nm setsockopt 42.Nd get and set options on sockets 43.Sh LIBRARY 44.Lb libc 45.Sh SYNOPSIS 46.In sys/types.h 47.In sys/socket.h 48.Ft int 49.Fn getsockopt "int s" "int level" "int optname" "void *optval" "socklen_t *optlen" 50.Ft int 51.Fn setsockopt "int s" "int level" "int optname" "const void *optval" "socklen_t optlen" 52.Sh DESCRIPTION 53.Fn Getsockopt 54and 55.Fn setsockopt 56manipulate the 57.Em options 58associated with a socket. Options may exist at multiple 59protocol levels; they are always present at the uppermost 60.Dq socket 61level. 62.Pp 63When manipulating socket options the level at which the 64option resides and the name of the option must be specified. 65To manipulate options at the socket level, 66.Fa level 67is specified as 68.Dv SOL_SOCKET . 69To manipulate options at any 70other level the protocol number of the appropriate protocol 71controlling the option is supplied. For example, 72to indicate that an option is to be interpreted by the 73.Tn TCP 74protocol, 75.Fa level 76should be set to the protocol number of 77.Tn TCP ; 78see 79.Xr getprotoent 3 . 80.Pp 81The parameters 82.Fa optval 83and 84.Fa optlen 85are used to access option values for 86.Fn setsockopt . 87For 88.Fn getsockopt 89they identify a buffer in which the value for the 90requested option(s) are to be returned. For 91.Fn getsockopt , 92.Fa optlen 93is a value-result parameter, initially containing the 94size of the buffer pointed to by 95.Fa optval , 96and modified on return to indicate the actual size of 97the value returned. If no option value is 98to be supplied or returned, 99.Fa optval 100may be NULL. 101.Pp 102.Fa Optname 103and any specified options are passed uninterpreted to the appropriate 104protocol module for interpretation. 105The include file 106.In sys/socket.h 107contains definitions for 108socket level options, described below. 109Options at other protocol levels vary in format and 110name; consult the appropriate entries in 111section 1124 of the manual. 113.Pp 114Most socket-level options utilize an 115.Fa int 116parameter for 117.Fa optval . 118For 119.Fn setsockopt , 120the parameter should be non-zero to enable a boolean option, 121or zero if the option is to be disabled. 122.Dv SO_LINGER 123uses a 124.Fa struct linger 125parameter, defined in 126.In sys/socket.h , 127which specifies the desired state of the option and the 128linger interval (see below). 129.Dv SO_SNDTIMEO 130and 131.Dv SO_RCVTIMEO 132use a 133.Fa struct timeval 134parameter, defined in 135.In sys/time.h . 136.Pp 137The following options are recognized at the socket level. 138Except as noted, each may be examined with 139.Fn getsockopt 140and set with 141.Fn setsockopt . 142.Bl -column SO_ACCEPTFILTER -offset indent 143.It Dv SO_DEBUG Ta "enables recording of debugging information" 144.It Dv SO_REUSEADDR Ta "enables local address reuse" 145.It Dv SO_REUSEPORT Ta "enables duplicate address and port bindings" 146.It Dv SO_KEEPALIVE Ta "enables keep connections alive" 147.It Dv SO_DONTROUTE Ta "enables routing bypass for outgoing messages" 148.It Dv SO_LINGER Ta "linger on close if data present" 149.It Dv SO_BROADCAST Ta "enables permission to transmit broadcast messages" 150.It Dv SO_OOBINLINE Ta "enables reception of out-of-band data in band" 151.It Dv SO_SNDBUF Ta "set buffer size for output" 152.It Dv SO_RCVBUF Ta "set buffer size for input" 153.It Dv SO_SNDLOWAT Ta "set minimum count for output" 154.It Dv SO_RCVLOWAT Ta "set minimum count for input" 155.It Dv SO_SNDTIMEO Ta "set timeout value for output" 156.It Dv SO_RCVTIMEO Ta "set timeout value for input" 157.It Dv SO_ACCEPTFILTER Ta "set accept filter on listening socket" 158.It Dv SO_TYPE Ta "get the type of the socket (get only)" 159.It Dv SO_ERROR Ta "get and clear error on the socket (get only)" 160.El 161.Pp 162.Dv SO_DEBUG 163enables debugging in the underlying protocol modules. 164.Dv SO_REUSEADDR 165indicates that the rules used in validating addresses supplied 166in a 167.Xr bind 2 168call should allow reuse of local addresses. 169.Dv SO_REUSEPORT 170allows completely duplicate bindings by multiple processes 171if they all set 172.Dv SO_REUSEPORT 173before binding the port. 174This option permits multiple instances of a program to each 175receive UDP/IP multicast or broadcast datagrams destined for the bound port. 176.Dv SO_KEEPALIVE 177enables the 178periodic transmission of messages on a connected socket. Should the 179connected party fail to respond to these messages, the connection is 180considered broken and processes using the socket are notified via a 181.Dv SIGPIPE 182signal when attempting to send data. 183.Dv SO_DONTROUTE 184indicates that outgoing messages should 185bypass the standard routing facilities. Instead, messages are directed 186to the appropriate network interface according to the network portion 187of the destination address. 188.Pp 189.Dv SO_LINGER 190controls the action taken when unsent messages 191are queued on socket and a 192.Xr close 2 193is performed. 194If the socket promises reliable delivery of data and 195.Dv SO_LINGER 196is set, 197the system will block the process on the 198.Xr close 2 199attempt until it is able to transmit the data or until it decides it 200is unable to deliver the information (a timeout period, termed the 201linger interval, is specified in seconds in the 202.Fn setsockopt 203call when 204.Dv SO_LINGER 205is requested). 206If 207.Dv SO_LINGER 208is disabled and a 209.Xr close 2 210is issued, the system will process the close in a manner that allows 211the process to continue as quickly as possible. 212.Pp 213The option 214.Dv SO_BROADCAST 215requests permission to send broadcast datagrams 216on the socket. 217Broadcast was a privileged operation in earlier versions of the system. 218With protocols that support out-of-band data, the 219.Dv SO_OOBINLINE 220option 221requests that out-of-band data be placed in the normal data input queue 222as received; it will then be accessible with 223.Xr recv 2 224or 225.Xr read 2 226calls without the 227.Dv MSG_OOB 228flag. 229Some protocols always behave as if this option is set. 230.Dv SO_SNDBUF 231and 232.Dv SO_RCVBUF 233are options to adjust the normal 234buffer sizes allocated for output and input buffers, respectively. 235The buffer size may be increased for high-volume connections, 236or may be decreased to limit the possible backlog of incoming data. 237The system places an absolute maximum on these values, which is accessible 238through the 239.Xr sysctl 3 240MIB variable 241.Va kern.ipc.maxsockbuf . 242.Pp 243.Dv SO_SNDLOWAT 244is an option to set the minimum count for output operations. 245Most output operations process all of the data supplied 246by the call, delivering data to the protocol for transmission 247and blocking as necessary for flow control. 248Nonblocking output operations will process as much data as permitted 249subject to flow control without blocking, but will process no data 250if flow control does not allow the smaller of the low water mark value 251or the entire request to be processed. 252A 253.Xr select 2 254operation testing the ability to write to a socket will return true 255only if the low water mark amount could be processed. 256The default value for 257.Dv SO_SNDLOWAT 258is set to a convenient size for network efficiency, often 1024. 259.Dv SO_RCVLOWAT 260is an option to set the minimum count for input operations. 261In general, receive calls will block until any (non-zero) amount of data 262is received, then return with the smaller of the amount available or the amount 263requested. 264The default value for 265.Dv SO_RCVLOWAT 266is 1. 267If 268.Dv SO_RCVLOWAT 269is set to a larger value, blocking receive calls normally 270wait until they have received the smaller of the low water mark value 271or the requested amount. 272Receive calls may still return less than the low water mark if an error 273occurs, a signal is caught, or the type of data next in the receive queue 274is different from that which was returned. 275.Pp 276.Dv SO_SNDTIMEO 277is an option to set a timeout value for output operations. 278It accepts a 279.Fa struct timeval 280parameter with the number of seconds and microseconds 281used to limit waits for output operations to complete. 282If a send operation has blocked for this much time, 283it returns with a partial count 284or with the error 285.Er EWOULDBLOCK 286if no data were sent. 287In the current implementation, this timer is restarted each time additional 288data are delivered to the protocol, 289implying that the limit applies to output portions ranging in size 290from the low water mark to the high water mark for output. 291.Dv SO_RCVTIMEO 292is an option to set a timeout value for input operations. 293It accepts a 294.Fa struct timeval 295parameter with the number of seconds and microseconds 296used to limit waits for input operations to complete. 297In the current implementation, this timer is restarted each time additional 298data are received by the protocol, 299and thus the limit is in effect an inactivity timer. 300If a receive operation has been blocked for this much time without 301receiving additional data, it returns with a short count 302or with the error 303.Er EWOULDBLOCK 304if no data were received. 305.Pp 306.Dv SO_ACCEPTFILTER 307places an 308.Xr accept_filter 9 309on the socket, 310which will filter incoming connections 311on a listening stream socket before being presented for 312.Xr accept 2 . 313Once more, 314.Xr listen 2 315must be called on the socket before 316trying to install the filter on it, 317or else the 318.Fn setsockopt 319call will fail. 320.Bd -literal 321struct accept_filter_arg { 322 char af_name[16]; 323 char af_arg[256-16]; 324}; 325.Ed 326.Pp 327.Fa optval 328should point to a 329.Fa struct accept_filter_arg 330that will select and configure the 331.Xr accept_filter 9 . 332.Fa af_name 333should be filled with the name of the accept filter 334that the application wishes to place on the listening socket. 335.Fa af_arg 336is an optional parameter that can be passed to the accept 337filter specified by 338.Fa af_name 339to provide additional configuration options at attach time. 340Passing in an 341.Fa optval 342of NULL will remove the filter. 343.Pp 344Finally, 345.Dv SO_TYPE 346and 347.Dv SO_ERROR 348are options used only with 349.Fn getsockopt . 350.Dv SO_TYPE 351returns the type of the socket, such as 352.Dv SOCK_STREAM ; 353it is useful for servers that inherit sockets on startup. 354.Dv SO_ERROR 355returns any pending error on the socket and clears 356the error status. 357It may be used to check for asynchronous errors on connected 358datagram sockets or for other asynchronous errors. 359.Sh RETURN VALUES 360.Rv -std 361.Sh ERRORS 362The call succeeds unless: 363.Bl -tag -width Er 364.It Bq Er EBADF 365The argument 366.Fa s 367is not a valid descriptor. 368.It Bq Er ENOTSOCK 369The argument 370.Fa s 371is a file, not a socket. 372.It Bq Er ENOPROTOOPT 373The option is unknown at the level indicated. 374.It Bq Er EFAULT 375The address pointed to by 376.Fa optval 377is not in a valid part of the process address space. 378For 379.Fn getsockopt , 380this error may also be returned if 381.Fa optlen 382is not in a valid part of the process address space. 383.It Bq Er EINVAL 384Installing an 385.Xr accept_filter 9 386on a non-listening socket was attempted. 387.El 388.Sh SEE ALSO 389.Xr ioctl 2 , 390.Xr socket 2 , 391.Xr getprotoent 3 , 392.Xr sysctl 3 , 393.Xr protocols 5 , 394.Xr sysctl 8 , 395.Xr accept_filter 9 396.Sh HISTORY 397The 398.Fn getsockopt 399system call appeared in 400.Bx 4.2 . 401.Sh BUGS 402Several of the socket options should be handled at lower levels of the system. 403