1.\" Copyright (c) 1983, 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 3. 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.\" 31.Dd May 2, 1995 32.Dt GETSOCKOPT 2 33.Os 34.Sh NAME 35.Nm getsockopt , 36.Nm setsockopt 37.Nd get and set options on sockets 38.Sh LIBRARY 39.Lb libc 40.Sh SYNOPSIS 41.In sys/types.h 42.In sys/socket.h 43.Ft int 44.Fn getsockopt "int s" "int level" "int optname" "void *optval" "socklen_t *optlen" 45.Ft int 46.Fn setsockopt "int s" "int level" "int optname" "const void *optval" "socklen_t optlen" 47.Sh DESCRIPTION 48.Fn Getsockopt 49and 50.Fn setsockopt 51manipulate the 52.Em options 53associated with a socket. Options may exist at multiple 54protocol levels; they are always present at the uppermost 55.Dq socket 56level. 57.Pp 58When manipulating socket options the level at which the 59option resides and the name of the option must be specified. 60To manipulate options at the socket level, 61.Fa level 62is specified as 63.Dv SOL_SOCKET . 64To manipulate options at any 65other level the protocol number of the appropriate protocol 66controlling the option is supplied. For example, 67to indicate that an option is to be interpreted by the 68.Tn TCP 69protocol, 70.Fa level 71should be set to the protocol number of 72.Tn TCP ; 73see 74.Xr getprotoent 3 . 75.Pp 76The parameters 77.Fa optval 78and 79.Fa optlen 80are used to access option values for 81.Fn setsockopt . 82For 83.Fn getsockopt 84they identify a buffer in which the value for the 85requested option(s) are to be returned. For 86.Fn getsockopt , 87.Fa optlen 88is a value-result parameter, initially containing the 89size of the buffer pointed to by 90.Fa optval , 91and modified on return to indicate the actual size of 92the value returned. If no option value is 93to be supplied or returned, 94.Fa optval 95may be NULL. 96.Pp 97.Fa Optname 98and any specified options are passed uninterpreted to the appropriate 99protocol module for interpretation. 100The include file 101.In sys/socket.h 102contains definitions for 103socket level options, described below. 104Options at other protocol levels vary in format and 105name; consult the appropriate entries in 106section 1074 of the manual. 108.Pp 109Most socket-level options utilize an 110.Fa int 111parameter for 112.Fa optval . 113For 114.Fn setsockopt , 115the parameter should be non-zero to enable a boolean option, 116or zero if the option is to be disabled. 117.Dv SO_LINGER 118uses a 119.Fa struct linger 120parameter, defined in 121.In sys/socket.h , 122which specifies the desired state of the option and the 123linger interval (see below). 124.Dv SO_SNDTIMEO 125and 126.Dv SO_RCVTIMEO 127use a 128.Fa struct timeval 129parameter, defined in 130.In sys/time.h . 131.Pp 132The following options are recognized at the socket level. 133Except as noted, each may be examined with 134.Fn getsockopt 135and set with 136.Fn setsockopt . 137.Bl -column SO_ACCEPTFILTER -offset indent 138.It Dv SO_DEBUG Ta "enables recording of debugging information" 139.It Dv SO_REUSEADDR Ta "enables local address reuse" 140.It Dv SO_REUSEPORT Ta "enables duplicate address and port bindings" 141.It Dv SO_KEEPALIVE Ta "enables keep connections alive" 142.It Dv SO_DONTROUTE Ta "enables routing bypass for outgoing messages" 143.It Dv SO_LINGER Ta "linger on close if data present" 144.It Dv SO_BROADCAST Ta "enables permission to transmit broadcast messages" 145.It Dv SO_OOBINLINE Ta "enables reception of out-of-band data in band" 146.It Dv SO_SNDBUF Ta "set buffer size for output" 147.It Dv SO_RCVBUF Ta "set buffer size for input" 148.It Dv SO_SNDLOWAT Ta "set minimum count for output" 149.It Dv SO_RCVLOWAT Ta "set minimum count for input" 150.It Dv SO_SNDTIMEO Ta "set timeout value for output" 151.It Dv SO_RCVTIMEO Ta "set timeout value for input" 152.It Dv SO_ACCEPTFILTER Ta "set accept filter on listening socket" 153.It Dv SO_TYPE Ta "get the type of the socket (get only)" 154.It Dv SO_ERROR Ta "get and clear error on the socket (get only)" 155.El 156.Pp 157.Dv SO_DEBUG 158enables debugging in the underlying protocol modules. 159.Dv SO_REUSEADDR 160indicates that the rules used in validating addresses supplied 161in a 162.Xr bind 2 163call should allow reuse of local addresses. 164.Dv SO_REUSEPORT 165allows completely duplicate bindings by multiple processes 166if they all set 167.Dv SO_REUSEPORT 168before binding the port. 169This option permits multiple instances of a program to each 170receive UDP/IP multicast or broadcast datagrams destined for the bound port. 171.Dv SO_KEEPALIVE 172enables the 173periodic transmission of messages on a connected socket. Should the 174connected party fail to respond to these messages, the connection is 175considered broken and processes using the socket are notified via a 176.Dv SIGPIPE 177signal when attempting to send data. 178.Dv SO_DONTROUTE 179indicates that outgoing messages should 180bypass the standard routing facilities. Instead, messages are directed 181to the appropriate network interface according to the network portion 182of the destination address. 183.Pp 184.Dv SO_LINGER 185controls the action taken when unsent messages 186are queued on socket and a 187.Xr close 2 188is performed. 189If the socket promises reliable delivery of data and 190.Dv SO_LINGER 191is set, 192the system will block the process on the 193.Xr close 2 194attempt until it is able to transmit the data or until it decides it 195is unable to deliver the information (a timeout period, termed the 196linger interval, is specified in seconds in the 197.Fn setsockopt 198call when 199.Dv SO_LINGER 200is requested). 201If 202.Dv SO_LINGER 203is disabled and a 204.Xr close 2 205is issued, the system will process the close in a manner that allows 206the process to continue as quickly as possible. 207.Pp 208The option 209.Dv SO_BROADCAST 210requests permission to send broadcast datagrams 211on the socket. 212Broadcast was a privileged operation in earlier versions of the system. 213With protocols that support out-of-band data, the 214.Dv SO_OOBINLINE 215option 216requests that out-of-band data be placed in the normal data input queue 217as received; it will then be accessible with 218.Xr recv 2 219or 220.Xr read 2 221calls without the 222.Dv MSG_OOB 223flag. 224Some protocols always behave as if this option is set. 225.Dv SO_SNDBUF 226and 227.Dv SO_RCVBUF 228are options to adjust the normal 229buffer sizes allocated for output and input buffers, respectively. 230The buffer size may be increased for high-volume connections, 231or may be decreased to limit the possible backlog of incoming data. 232The system places an absolute maximum on these values, which is accessible 233through the 234.Xr sysctl 3 235MIB variable 236.Va kern.ipc.maxsockbuf . 237.Pp 238.Dv SO_SNDLOWAT 239is an option to set the minimum count for output operations. 240Most output operations process all of the data supplied 241by the call, delivering data to the protocol for transmission 242and blocking as necessary for flow control. 243Nonblocking output operations will process as much data as permitted 244subject to flow control without blocking, but will process no data 245if flow control does not allow the smaller of the low water mark value 246or the entire request to be processed. 247A 248.Xr select 2 249operation testing the ability to write to a socket will return true 250only if the low water mark amount could be processed. 251The default value for 252.Dv SO_SNDLOWAT 253is set to a convenient size for network efficiency, often 1024. 254.Dv SO_RCVLOWAT 255is an option to set the minimum count for input operations. 256In general, receive calls will block until any (non-zero) amount of data 257is received, then return with the smaller of the amount available or the amount 258requested. 259The default value for 260.Dv SO_RCVLOWAT 261is 1. 262If 263.Dv SO_RCVLOWAT 264is set to a larger value, blocking receive calls normally 265wait until they have received the smaller of the low water mark value 266or the requested amount. 267Receive calls may still return less than the low water mark if an error 268occurs, a signal is caught, or the type of data next in the receive queue 269is different from that which was returned. 270.Pp 271.Dv SO_SNDTIMEO 272is an option to set a timeout value for output operations. 273It accepts a 274.Fa struct timeval 275parameter with the number of seconds and microseconds 276used to limit waits for output operations to complete. 277If a send operation has blocked for this much time, 278it returns with a partial count 279or with the error 280.Er EWOULDBLOCK 281if no data were sent. 282In the current implementation, this timer is restarted each time additional 283data are delivered to the protocol, 284implying that the limit applies to output portions ranging in size 285from the low water mark to the high water mark for output. 286.Dv SO_RCVTIMEO 287is an option to set a timeout value for input operations. 288It accepts a 289.Fa struct timeval 290parameter with the number of seconds and microseconds 291used to limit waits for input operations to complete. 292In the current implementation, this timer is restarted each time additional 293data are received by the protocol, 294and thus the limit is in effect an inactivity timer. 295If a receive operation has been blocked for this much time without 296receiving additional data, it returns with a short count 297or with the error 298.Er EWOULDBLOCK 299if no data were received. 300.Pp 301.Dv SO_ACCEPTFILTER 302places an 303.Xr accept_filter 9 304on the socket, 305which will filter incoming connections 306on a listening stream socket before being presented for 307.Xr accept 2 . 308Once more, 309.Xr listen 2 310must be called on the socket before 311trying to install the filter on it, 312or else the 313.Fn setsockopt 314call will fail. 315.Bd -literal 316struct accept_filter_arg { 317 char af_name[16]; 318 char af_arg[256-16]; 319}; 320.Ed 321.Pp 322.Fa optval 323should point to a 324.Fa struct accept_filter_arg 325that will select and configure the 326.Xr accept_filter 9 . 327.Fa af_name 328should be filled with the name of the accept filter 329that the application wishes to place on the listening socket. 330.Fa af_arg 331is an optional parameter that can be passed to the accept 332filter specified by 333.Fa af_name 334to provide additional configuration options at attach time. 335Passing in an 336.Fa optval 337of NULL will remove the filter. 338.Pp 339Finally, 340.Dv SO_TYPE 341and 342.Dv SO_ERROR 343are options used only with 344.Fn getsockopt . 345.Dv SO_TYPE 346returns the type of the socket, such as 347.Dv SOCK_STREAM ; 348it is useful for servers that inherit sockets on startup. 349.Dv SO_ERROR 350returns any pending error on the socket and clears 351the error status. 352It may be used to check for asynchronous errors on connected 353datagram sockets or for other asynchronous errors. 354.Sh RETURN VALUES 355.Rv -std 356.Sh ERRORS 357The call succeeds unless: 358.Bl -tag -width Er 359.It Bq Er EBADF 360The argument 361.Fa s 362is not a valid descriptor. 363.It Bq Er ENOTSOCK 364The argument 365.Fa s 366is a file, not a socket. 367.It Bq Er ENOPROTOOPT 368The option is unknown at the level indicated. 369.It Bq Er EFAULT 370The address pointed to by 371.Fa optval 372is not in a valid part of the process address space. 373For 374.Fn getsockopt , 375this error may also be returned if 376.Fa optlen 377is not in a valid part of the process address space. 378.It Bq Er EINVAL 379Installing an 380.Xr accept_filter 9 381on a non-listening socket was attempted. 382.El 383.Sh SEE ALSO 384.Xr ioctl 2 , 385.Xr socket 2 , 386.Xr getprotoent 3 , 387.Xr sysctl 3 , 388.Xr protocols 5 , 389.Xr sysctl 8 , 390.Xr accept_filter 9 391.Sh HISTORY 392The 393.Fn getsockopt 394system call appeared in 395.Bx 4.2 . 396.Sh BUGS 397Several of the socket options should be handled at lower levels of the system. 398