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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 8.3 (Berkeley) 4/19/94 33.\" 34.Dd April 19, 1994 35.Dt GETSOCKOPT 2 36.Os BSD 4.3r 37.Sh NAME 38.Nm getsockopt , 39.Nm setsockopt 40.Nd get and set options on sockets 41.Sh SYNOPSIS 42.Fd #include <sys/types.h> 43.Fd #include <sys/socket.h> 44.Ft int 45.Fn getsockopt "int s" "int level" "int optname" "void *optval" "int *optlen" 46.Ft int 47.Fn setsockopt "int s" "int level" "int optname" "const void *optval" "int 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.Ao Pa sys/socket.h Ac 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.Ao Pa sys/socket.h Ac , 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.Ao Pa sys/time.h Ac . 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_OOBINLINE -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_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 is set, 191the system will block the process on the 192.Xr close 193attempt until it is able to transmit the data or until it decides it 194is unable to deliver the information (a timeout period, termed the 195linger interval, is specified in the 196.Fn setsockopt 197call when 198.Dv SO_LINGER 199is requested). 200If 201.Dv SO_LINGER 202is disabled and a 203.Xr close 204is issued, the system will process the close in a manner that allows 205the process to continue as quickly as possible. 206.Pp 207The option 208.Dv SO_BROADCAST 209requests permission to send broadcast datagrams 210on the socket. 211Broadcast was a privileged operation in earlier versions of the system. 212With protocols that support out-of-band data, the 213.Dv SO_OOBINLINE 214option 215requests that out-of-band data be placed in the normal data input queue 216as received; it will then be accessible with 217.Xr recv 218or 219.Xr read 220calls without the 221.Dv MSG_OOB 222flag. 223Some protocols always behave as if this option is set. 224.Dv SO_SNDBUF 225and 226.Dv SO_RCVBUF 227are options to adjust the normal 228buffer sizes allocated for output and input buffers, respectively. 229The buffer size may be increased for high-volume connections, 230or may be decreased to limit the possible backlog of incoming data. 231The system places an absolute limit on these values. 232.Pp 233.Dv SO_SNDLOWAT 234is an option to set the minimum count for output operations. 235Most output operations process all of the data supplied 236by the call, delivering data to the protocol for transmission 237and blocking as necessary for flow control. 238Nonblocking output operations will process as much data as permitted 239subject to flow control without blocking, but will process no data 240if flow control does not allow the smaller of the low water mark value 241or the entire request to be processed. 242A 243.Xr select 2 244operation testing the ability to write to a socket will return true 245only if the low water mark amount could be processed. 246The default value for 247.Dv SO_SNDLOWAT 248is set to a convenient size for network efficiency, often 1024. 249.Dv SO_RCVLOWAT 250is an option to set the minimum count for input operations. 251In general, receive calls will block until any (non-zero) amount of data 252is received, then return with the smaller of the amount available or the amount 253requested. 254The default value for 255.Dv SO_RCVLOWAT 256is 1. 257If 258.Dv SO_RCVLOWAT 259is set to a larger value, blocking receive calls normally 260wait until they have received the smaller of the low water mark value 261or the requested amount. 262Receive calls may still return less than the low water mark if an error 263occurs, a signal is caught, or the type of data next in the receive queue 264is different than that returned. 265.Pp 266.Dv SO_SNDTIMEO 267is an option to set a timeout value for output operations. 268It accepts a 269.Fa struct timeval 270parameter with the number of seconds and microseconds 271used to limit waits for output operations to complete. 272If a send operation has blocked for this much time, 273it returns with a partial count 274or with the error 275.Er EWOULDBLOCK 276if no data were sent. 277In the current implementation, this timer is restarted each time additional 278data are delivered to the protocol, 279implying that the limit applies to output portions ranging in size 280from the low water mark to the high water mark for output. 281.Dv SO_RCVTIMEO 282is an option to set a timeout value for input operations. 283It accepts a 284.Fa struct timeval 285parameter with the number of seconds and microseconds 286used to limit waits for input operations to complete. 287In the current implementation, this timer is restarted each time additional 288data are received by the protocol, 289and thus the limit is in effect an inactivity timer. 290If a receive operation has been blocked for this much time without 291receiving additional data, it returns with a short count 292or with the error 293.Er EWOULDBLOCK 294if no data were received. 295.Pp 296Finally, 297.Dv SO_TYPE 298and 299.Dv SO_ERROR 300are options used only with 301.Fn getsockopt . 302.Dv SO_TYPE 303returns the type of the socket, such as 304.Dv SOCK_STREAM ; 305it is useful for servers that inherit sockets on startup. 306.Dv SO_ERROR 307returns any pending error on the socket and clears 308the error status. 309It may be used to check for asynchronous errors on connected 310datagram sockets or for other asynchronous errors. 311.Sh RETURN VALUES 312A 0 is returned if the call succeeds, -1 if it fails. 313.Sh ERRORS 314The call succeeds unless: 315.Bl -tag -width ENOPROTOOPTAA 316.It Bq Er EBADF 317The argument 318.Fa s 319is not a valid descriptor. 320.It Bq Er ENOTSOCK 321The argument 322.Fa s 323is a file, not a socket. 324.It Bq Er ENOPROTOOPT 325The option is unknown at the level indicated. 326.It Bq Er EFAULT 327The address pointed to by 328.Fa optval 329is not in a valid part of the process address space. 330For 331.Fn getsockopt , 332this error may also be returned if 333.Fa optlen 334is not in a valid part of the process address space. 335.El 336.Sh SEE ALSO 337.Xr ioctl 2 , 338.Xr socket 2 , 339.Xr getprotoent 3 340.Xr protocols 5 341.Sh BUGS 342Several of the socket options should be handled at lower levels of the system. 343.Sh HISTORY 344The 345.Nm 346system call appeared in 347.Bx 4.2 . 348