1.\" $NetBSD: getsockopt.2,v 1.23 2002/02/08 01:28:18 ross Exp $ 2.\" 3.\" Copyright (c) 1983, 1991, 1993 4.\" The Regents of the University of California. All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 3. All advertising materials mentioning features or use of this software 15.\" must display the following acknowledgement: 16.\" This product includes software developed by the University of 17.\" California, Berkeley and its contributors. 18.\" 4. Neither the name of the University nor the names of its contributors 19.\" may be used to endorse or promote products derived from this software 20.\" without specific prior written permission. 21.\" 22.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 23.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 24.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 25.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 26.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 27.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 28.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 29.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 31.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32.\" SUCH DAMAGE. 33.\" 34.\" @(#)getsockopt.2 8.4 (Berkeley) 5/2/95 35.\" 36.Dd October 22, 2001 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.Fd #include \*[Lt]sys/socket.h\*[Gt] 47.Ft int 48.Fn getsockopt "int s" "int level" "int optname" "void * restrict optval" "socklen_t * restrict optlen" 49.Ft int 50.Fn setsockopt "int s" "int level" "int optname" "const void *optval" "socklen_t optlen" 51.Sh DESCRIPTION 52.Fn getsockopt 53and 54.Fn setsockopt 55manipulate the 56.Em options 57associated with a socket. Options may exist at multiple 58protocol levels; they are always present at the uppermost 59.Dq socket 60level. 61.Pp 62When manipulating socket options the level at which the 63option resides and the name of the option must be specified. 64To manipulate options at the socket level, 65.Fa level 66is specified as 67.Dv SOL_SOCKET . 68To manipulate options at any 69other level the protocol number of the appropriate protocol 70controlling the option is supplied. For example, 71to indicate that an option is to be interpreted by the 72.Tn TCP 73protocol, 74.Fa level 75should be set to the protocol number of 76.Tn TCP ; 77see 78.Xr getprotoent 3 . 79.Pp 80The parameters 81.Fa optval 82and 83.Fa optlen 84are used to access option values for 85.Fn setsockopt . 86For 87.Fn getsockopt 88they identify a buffer in which the value for the 89requested option(s) are to be returned. For 90.Fn getsockopt , 91.Fa optlen 92is a value-result parameter, initially containing the 93size of the buffer pointed to by 94.Fa optval , 95and modified on return to indicate the actual size of 96the value returned. If no option value is 97to be supplied or returned, 98.Fa optval 99may be NULL. 100.Pp 101.Fa optname 102and any specified options are passed uninterpreted to the appropriate 103protocol module for interpretation. 104The include file 105.Ao Pa sys/socket.h Ac 106contains definitions for 107socket level options, described below. 108Options at other protocol levels vary in format and 109name; consult the appropriate entries in 110section 1114 of the manual. 112.Pp 113Most socket-level options utilize an 114.Fa int 115parameter for 116.Fa optval . 117For 118.Fn setsockopt , 119the parameter should be non-zero to enable a boolean option, 120or zero if the option is to be disabled. 121.Dv SO_LINGER 122uses a 123.Fa struct linger 124parameter, defined in 125.Ao Pa sys/socket.h Ac , 126which specifies the desired state of the option and the 127linger interval (see below). 128.Dv SO_SNDTIMEO 129and 130.Dv SO_RCVTIMEO 131use a 132.Fa struct timeval 133parameter, defined in 134.Ao Pa sys/time.h Ac . 135.Pp 136The following options are recognized at the socket level. 137Except as noted, each may be examined with 138.Fn getsockopt 139and set with 140.Fn setsockopt . 141.Bl -column SO_OOBINLINE -offset indent 142.It Dv SO_DEBUG Ta "enables recording of debugging information" 143.It Dv SO_REUSEADDR Ta "enables local address reuse" 144.It Dv SO_REUSEPORT Ta "enables duplicate address and port bindings" 145.It Dv SO_KEEPALIVE Ta "enables keep connections alive" 146.It Dv SO_DONTROUTE Ta "enables routing bypass for outgoing messages" 147.It Dv SO_LINGER Ta "linger on close if data present" 148.It Dv SO_BROADCAST Ta "enables permission to transmit broadcast messages" 149.It Dv SO_OOBINLINE Ta "enables reception of out-of-band data in band" 150.It Dv SO_SNDBUF Ta "set buffer size for output" 151.It Dv SO_RCVBUF Ta "set buffer size for input" 152.It Dv SO_SNDLOWAT Ta "set minimum count for output" 153.It Dv SO_RCVLOWAT Ta "set minimum count for input" 154.It Dv SO_SNDTIMEO Ta "set timeout value for output" 155.It Dv SO_RCVTIMEO Ta "set timeout value for input" 156.It Dv SO_TIMESTAMP Ta "enables reception of a timestamp with datagrams" 157.It Dv SO_TYPE Ta "get the type of the socket (get only)" 158.It Dv SO_ERROR Ta "get and clear error on the socket (get only)" 159.El 160.Pp 161.Dv SO_DEBUG 162enables debugging in the underlying protocol modules. 163.Dv SO_REUSEADDR 164indicates that the rules used in validating addresses supplied 165in a 166.Xr bind 2 167call should allow reuse of local addresses. 168.Dv SO_REUSEPORT 169allows completely duplicate bindings by multiple processes 170if they all set 171.Dv SO_REUSEPORT 172before binding the port. 173This option permits multiple instances of a program to each 174receive UDP/IP multicast or broadcast datagrams destined for the bound port. 175.Dv SO_KEEPALIVE 176enables the 177periodic transmission of messages on a connected socket. Should the 178connected party fail to respond to these messages, the connection is 179considered broken and processes using the socket are notified via a 180.Dv SIGPIPE 181signal when attempting to send data. 182.Dv SO_DONTROUTE 183indicates that outgoing messages should 184bypass the standard routing facilities. Instead, messages are directed 185to the appropriate network interface according to the network portion 186of the destination address. 187.Pp 188.Dv SO_LINGER 189controls the action taken when unsent messages 190are queued on socket and a 191.Xr close 2 192is performed. 193If the socket promises reliable delivery of data and 194.Dv SO_LINGER 195is set, the system will block the process on the 196.Xr close 2 197attempt until it is able to transmit the data or until it decides it 198is unable to deliver the information (a timeout period, measured in 199seconds, termed the linger interval, is specified in the 200.Fn setsockopt 201call when 202.Dv SO_LINGER 203is requested). 204If 205.Dv SO_LINGER 206is disabled and a 207.Xr close 2 208is issued, the system will process the close in a manner that allows 209the process to continue as quickly as possible. 210.Pp 211The option 212.Dv SO_BROADCAST 213requests permission to send broadcast datagrams 214on the socket. 215Broadcast was a privileged operation in earlier versions of the system. 216With protocols that support out-of-band data, the 217.Dv SO_OOBINLINE 218option 219requests that out-of-band data be placed in the normal data input queue 220as received; it will then be accessible with 221.Xr recv 2 222or 223.Xr read 2 224calls without the 225.Dv MSG_OOB 226flag. 227Some protocols always behave as if this option is set. 228.Dv SO_SNDBUF 229and 230.Dv SO_RCVBUF 231are options to adjust the normal 232buffer sizes allocated for output and input buffers, respectively. 233The buffer size may be increased for high-volume connections, 234or may be decreased to limit the possible backlog of incoming data. 235The system places an absolute limit on these values. 236.Pp 237.Dv SO_SNDLOWAT 238is an option to set the minimum count for output operations. 239Most output operations process all of the data supplied 240by the call, delivering data to the protocol for transmission 241and blocking as necessary for flow control. 242Nonblocking output operations will process as much data as permitted 243subject to flow control without blocking, but will process no data 244if flow control does not allow the smaller of the low water mark value 245or the entire request to be processed. 246A 247.Xr select 2 248or 249.Xr poll 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 than that 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 EAGAIN 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 EAGAIN 300if no data were received. 301.Pp 302If the 303.Dv SO_TIMESTAMP 304option is enabled on a 305.Dv SOCK_DGRAM 306socket, the 307.Xr recvmsg 2 308call will return a timestamp corresponding to when the datagram was 309received. 310The msg_control field in the msghdr structure points to a buffer 311that contains a cmsghdr structure followed by a struct timeval. 312The cmsghdr fields have the following values: 313.Bd -literal 314cmsg_len = sizeof(struct timeval) 315cmsg_level = SOL_SOCKET 316cmsg_type = SCM_TIMESTAMP 317.Ed 318.Pp 319Finally, 320.Dv SO_TYPE 321and 322.Dv SO_ERROR 323are options used only with 324.Fn getsockopt . 325.Dv SO_TYPE 326returns the type of the socket, such as 327.Dv SOCK_STREAM ; 328it is useful for servers that inherit sockets on startup. 329.Dv SO_ERROR 330returns any pending error on the socket and clears 331the error status. 332It may be used to check for asynchronous errors on connected 333datagram sockets or for other asynchronous errors. 334.Sh RETURN VALUES 335A 0 is returned if the call succeeds, -1 if it fails. 336.Sh ERRORS 337The call succeeds unless: 338.Bl -tag -width Er 339.It Bq Er EBADF 340The argument 341.Fa s 342is not a valid descriptor. 343.It Bq Er ENOTSOCK 344The argument 345.Fa s 346is a file, not a socket. 347.It Bq Er ENOPROTOOPT 348The option is unknown at the level indicated. 349.It Bq Er EFAULT 350The address pointed to by 351.Fa optval 352is not in a valid part of the process address space. 353For 354.Fn getsockopt , 355this error may also be returned if 356.Fa optlen 357is not in a valid part of the process address space. 358.El 359.Sh SEE ALSO 360.Xr ioctl 2 , 361.Xr poll 2 , 362.Xr select 2 , 363.Xr socket 2 , 364.Xr getprotoent 3 , 365.Xr protocols 5 366.Sh HISTORY 367The 368.Fn getsockopt 369system call appeared in 370.Bx 4.2 . 371.Sh BUGS 372Several of the socket options should be handled at lower levels of the system. 373