1.\" Copyright (c) 1983, 1991 The Regents of the University of California. 2.\" 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. All advertising materials mentioning features or use of this software 13.\" must display the following acknowledgement: 14.\" This product includes software developed by the University of 15.\" California, Berkeley and its contributors. 16.\" 4. 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.\" from: @(#)getsockopt.2 6.9 (Berkeley) 5/1/91 33.\" $Id: getsockopt.2,v 1.6 1994/03/16 02:04:14 cgd Exp $ 34.\" 35.Dd May 1, 1991 36.Dt GETSOCKOPT 2 37.Os BSD 4.3r 38.Sh NAME 39.Nm getsockopt , 40.Nm setsockopt 41.Nd get and set options on sockets 42.Sh SYNOPSIS 43.Fd #include <sys/types.h> 44.Fd #include <sys/socket.h> 45.Ft int 46.Fn getsockopt "int s" "int level" "int optname" "void *optval" "int *optlen" 47.Ft int 48.Fn setsockopt "int s" "int level" "int optname" "const void *optval" "int optlen" 49.Sh DESCRIPTION 50.Fn Getsockopt 51and 52.Fn setsockopt 53manipulate the 54.Em options 55associated with a socket. Options may exist at multiple 56protocol levels; they are always present at the uppermost 57.Dq socket 58level. 59.Pp 60When manipulating socket options the level at which the 61option resides and the name of the option must be specified. 62To manipulate options at the socket level, 63.Fa level 64is specified as 65.Dv SOL_SOCKET . 66To manipulate options at any 67other level the protocol number of the appropriate protocol 68controlling the option is supplied. For example, 69to indicate that an option is to be interpreted by the 70.Tn TCP 71protocol, 72.Fa level 73should be set to the protocol number of 74.Tn TCP ; 75see 76.Xr getprotoent 3 . 77.Pp 78The parameters 79.Fa optval 80and 81.Fa optlen 82are used to access option values for 83.Fn setsockopt . 84For 85.Fn getsockopt 86they identify a buffer in which the value for the 87requested option(s) are to be returned. For 88.Fn getsockopt , 89.Fa optlen 90is a value-result parameter, initially containing the 91size of the buffer pointed to by 92.Fa optval , 93and modified on return to indicate the actual size of 94the value returned. If no option value is 95to be supplied or returned, 96.Fa optval 97may be NULL. 98.Pp 99.Fa Optname 100and any specified options are passed uninterpreted to the appropriate 101protocol module for interpretation. 102The include file 103.Ao Pa sys/socket.h Ac 104contains definitions for 105socket level options, described below. 106Options at other protocol levels vary in format and 107name; consult the appropriate entries in 108section 1094 of the manual. 110.Pp 111Most socket-level options utilize an 112.Fa int 113parameter for 114.Fa optval . 115For 116.Fn setsockopt , 117the parameter should be non-zero to enable a boolean option, 118or zero if the option is to be disabled. 119.Dv SO_LINGER 120uses a 121.Fa struct linger 122parameter, defined in 123.Ao Pa sys/socket.h Ac , 124which specifies the desired state of the option and the 125linger interval (see below). 126.Dv SO_SNDTIMEO 127and 128.Dv SO_RCVTIMEO 129use a 130.Fa struct timeval 131parameter, defined in 132.Ao Pa sys/time.h Ac . 133.Pp 134The following options are recognized at the socket level. 135Except as noted, each may be examined with 136.Fn getsockopt 137and set with 138.Fn setsockopt . 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_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_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_KEEPALIVE 165enables the 166periodic transmission of messages on a connected socket. Should the 167connected party fail to respond to these messages, the connection is 168considered broken and processes using the socket are notified via a 169.Dv SIGPIPE 170signal when attempting to send data. 171.Dv SO_DONTROUTE 172indicates that outgoing messages should 173bypass the standard routing facilities. Instead, messages are directed 174to the appropriate network interface according to the network portion 175of the destination address. 176.Pp 177.Dv SO_LINGER 178controls the action taken when unsent messages 179are queued on socket and a 180.Xr close 2 181is performed. 182If the socket promises reliable delivery of data and 183.Dv SO_LINGER is set, 184the system will block the process on the 185.Xr close 186attempt until it is able to transmit the data or until it decides it 187is unable to deliver the information (a timeout period, termed the 188linger interval, is specified in the 189.Fn setsockopt 190call when 191.Dv SO_LINGER 192is requested). 193If 194.Dv SO_LINGER 195is disabled and a 196.Xr close 197is issued, the system will process the close in a manner that allows 198the process to continue as quickly as possible. 199.Pp 200The option 201.Dv SO_BROADCAST 202requests permission to send broadcast datagrams 203on the socket. 204Broadcast was a privileged operation in earlier versions of the system. 205With protocols that support out-of-band data, the 206.Dv SO_OOBINLINE 207option 208requests that out-of-band data be placed in the normal data input queue 209as received; it will then be accessible with 210.Xr recv 211or 212.Xr read 213calls without the 214.Dv MSG_OOB 215flag. 216Some protocols always behave as if this option is set. 217.Dv SO_SNDBUF 218and 219.Dv SO_RCVBUF 220are options to adjust the normal 221buffer sizes allocated for output and input buffers, respectively. 222The buffer size may be increased for high-volume connections, 223or may be decreased to limit the possible backlog of incoming data. 224The system places an absolute limit on these values. 225.Pp 226.Dv SO_SNDLOWAT 227is an option to set the minimum count for output operations. 228Most output operations process all of the data supplied 229by the call, delivering data to the protocol for transmission 230and blocking as necessary for flow control. 231Nonblocking output operations will process as much data as permitted 232subject to flow control without blocking, but will process no data 233if flow control does not allow the smaller of the low water mark value 234or the entire request to be processed. 235A 236.Xr select 2 237operation testing the ability to write to a socket will return true 238only if the low water mark amount could be processed. 239The default value for 240.Dv SO_SNDLOWAT 241is set to a convenient size for network efficiency, often 1024. 242.Dv SO_RCVLOWAT 243is an option to set the minimum count for input operations. 244In general, receive calls will block until any (non-zero) amount of data 245is received, then return with smaller of the amount available or the amount 246requested. 247The default value for 248.Dv SO_RCVLOWAT 249is 1. 250If 251.Dv SO_RCVLOWAT 252is set to a larger value, blocking receive calls normally 253wait until they have received the smaller of the low water mark value 254or the requested amount. 255Receive calls may still return less than the low water mark if an error 256occurs, a signal is caught, or the type of data next in the receive queue 257is different than that returned. 258.Pp 259.Dv SO_SNDTIMEO 260is an option to set a timeout value for output operations. 261It accepts a 262.Fa struct timeval 263parameter with the number of seconds and microseconds 264used to limit waits for output operations to complete. 265If a send operation has blocked for this much time, 266it returns with a partial count 267or with the error 268.Er EWOULDBLOCK 269if no data were sent. 270In the current implementation, this timer is restarted each time additional 271data are delivered to the protocol, 272implying that the limit applies to output portions ranging in size 273from the low water mark to the high water mark for output. 274.Dv SO_RCVTIMEO 275is an option to set a timeout value for input operations. 276It accepts a 277.Fa struct timeval 278parameter with the number of seconds and microseconds 279used to limit waits for input operations to complete. 280In the current implementation, this timer is restarted each time additional 281data are received by the protocol, 282and thus the limit is in effect an inactivity timer. 283If a receive operation has been blocked for this much time without 284receiving additional data, it returns with a short count 285or with the error 286.Er EWOULDBLOCK 287if no data were received. 288.Pp 289Finally, 290.Dv SO_TYPE 291and 292.Dv SO_ERROR 293are options used only with 294.Fn setsockopt . 295.Dv SO_TYPE 296returns the type of the socket, such as 297.Dv SOCK_STREAM ; 298it is useful for servers that inherit sockets on startup. 299.Dv SO_ERROR 300returns any pending error on the socket and clears 301the error status. 302It may be used to check for asynchronous errors on connected 303datagram sockets or for other asynchronous errors. 304.Sh RETURN VALUES 305A 0 is returned if the call succeeds, -1 if it fails. 306.Sh ERRORS 307The call succeeds unless: 308.Bl -tag -width Er 309.It Bq Er EBADF 310The argument 311.Fa s 312is not a valid descriptor. 313.It Bq Er ENOTSOCK 314The argument 315.Fa s 316is a file, not a socket. 317.It Bq Er ENOPROTOOPT 318The option is unknown at the level indicated. 319.It Bq Er EFAULT 320The address pointed to by 321.Fa optval 322is not in a valid part of the process address space. 323For 324.Fn getsockopt , 325this error may also be returned if 326.Fa optlen 327is not in a valid part of the process address space. 328.El 329.Sh SEE ALSO 330.Xr ioctl 2 , 331.Xr socket 2 , 332.Xr getprotoent 3 333.Xr protocols 5 334.Sh BUGS 335Several of the socket options should be handled at lower levels of the system. 336.Sh HISTORY 337The 338.Fn getsockopt 339system call appeared in 340.Bx 4.2 . 341