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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.\" From: @(#)socket.2 8.1 (Berkeley) 6/4/93 29.\" $FreeBSD$ 30.\" 31.Dd March 19, 2013 32.Dt SOCKET 2 33.Os 34.Sh NAME 35.Nm socket 36.Nd create an endpoint for communication 37.Sh LIBRARY 38.Lb libc 39.Sh SYNOPSIS 40.In sys/types.h 41.In sys/socket.h 42.Ft int 43.Fn socket "int domain" "int type" "int protocol" 44.Sh DESCRIPTION 45The 46.Fn socket 47system call 48creates an endpoint for communication and returns a descriptor. 49.Pp 50The 51.Fa domain 52argument specifies a communications domain within which 53communication will take place; this selects the protocol family 54which should be used. 55These families are defined in the include file 56.In sys/socket.h . 57The currently understood formats are: 58.Pp 59.Bd -literal -offset indent -compact 60PF_LOCAL Host-internal protocols, formerly called PF_UNIX, 61PF_UNIX Host-internal protocols, deprecated, use PF_LOCAL, 62PF_INET Internet version 4 protocols, 63PF_PUP PUP protocols, like BSP, 64PF_APPLETALK AppleTalk protocols, 65PF_ROUTE Internal Routing protocol, 66PF_LINK Link layer interface, 67PF_IPX Novell Internet Packet eXchange protocol, 68PF_RTIP Help Identify RTIP packets, 69PF_PIP Help Identify PIP packets, 70PF_ISDN Integrated Services Digital Network, 71PF_KEY Internal key-management function, 72PF_INET6 Internet version 6 protocols, 73PF_NATM Native ATM access, 74PF_ATM ATM, 75PF_NETGRAPH Netgraph sockets 76.Ed 77.Pp 78The socket has the indicated 79.Fa type , 80which specifies the semantics of communication. 81Currently 82defined types are: 83.Pp 84.Bd -literal -offset indent -compact 85SOCK_STREAM Stream socket, 86SOCK_DGRAM Datagram socket, 87SOCK_RAW Raw-protocol interface, 88SOCK_RDM Reliably-delivered packet, 89SOCK_SEQPACKET Sequenced packet stream 90.Ed 91.Pp 92A 93.Dv SOCK_STREAM 94type provides sequenced, reliable, 95two-way connection based byte streams. 96An out-of-band data transmission mechanism may be supported. 97A 98.Dv SOCK_DGRAM 99socket supports 100datagrams (connectionless, unreliable messages of 101a fixed (typically small) maximum length). 102A 103.Dv SOCK_SEQPACKET 104socket may provide a sequenced, reliable, 105two-way connection-based data transmission path for datagrams 106of fixed maximum length; a consumer may be required to read 107an entire packet with each read system call. 108This facility is protocol specific, and presently unimplemented. 109.Dv SOCK_RAW 110sockets provide access to internal network protocols and interfaces. 111The types 112.Dv SOCK_RAW , 113which is available only to the super-user, and 114.Dv SOCK_RDM , 115which is planned, 116but not yet implemented, are not described here. 117.Pp 118Additionally, the following flags are allowed in the 119.Fa type 120argument: 121.Pp 122.Bd -literal -offset indent -compact 123SOCK_CLOEXEC Set close-on-exec on the new descriptor, 124SOCK_NONBLOCK Set non-blocking mode on the new socket 125.Ed 126.Pp 127The 128.Fa protocol 129argument 130specifies a particular protocol to be used with the socket. 131Normally only a single protocol exists to support a particular 132socket type within a given protocol family. 133However, it is possible 134that many protocols may exist, in which case a particular protocol 135must be specified in this manner. 136The protocol number to use is 137particular to the 138.Dq "communication domain" 139in which communication 140is to take place; see 141.Xr protocols 5 . 142.Pp 143The 144.Fa protocol 145argument may be set to zero (0) to request the default 146implementation of a socket type for the protocol, if any. 147.Pp 148Sockets of type 149.Dv SOCK_STREAM 150are full-duplex byte streams, similar 151to pipes. 152A stream socket must be in a 153.Em connected 154state before any data may be sent or received 155on it. 156A connection to another socket is created with a 157.Xr connect 2 158system call. 159Once connected, data may be transferred using 160.Xr read 2 161and 162.Xr write 2 163calls or some variant of the 164.Xr send 2 165and 166.Xr recv 2 167functions. 168(Some protocol families, such as the Internet family, 169support the notion of an 170.Dq implied connect , 171which permits data to be sent piggybacked onto a connect operation by 172using the 173.Xr sendto 2 174system call.) 175When a session has been completed a 176.Xr close 2 177may be performed. 178Out-of-band data may also be transmitted as described in 179.Xr send 2 180and received as described in 181.Xr recv 2 . 182.Pp 183The communications protocols used to implement a 184.Dv SOCK_STREAM 185ensure that data 186is not lost or duplicated. 187If a piece of data for which the 188peer protocol has buffer space cannot be successfully transmitted 189within a reasonable length of time, then 190the connection is considered broken and calls 191will indicate an error with 192-1 returns and with 193.Er ETIMEDOUT 194as the specific code 195in the global variable 196.Va errno . 197The protocols optionally keep sockets 198.Dq warm 199by forcing transmissions 200roughly every minute in the absence of other activity. 201An error is then indicated if no response can be 202elicited on an otherwise 203idle connection for an extended period (e.g.\& 5 minutes). 204By default, a 205.Dv SIGPIPE 206signal is raised if a process sends 207on a broken stream, but this behavior may be inhibited via 208.Xr setsockopt 2 . 209.Pp 210.Dv SOCK_SEQPACKET 211sockets employ the same system calls 212as 213.Dv SOCK_STREAM 214sockets. 215The only difference 216is that 217.Xr read 2 218calls will return only the amount of data requested, 219and any remaining in the arriving packet will be discarded. 220.Pp 221.Dv SOCK_DGRAM 222and 223.Dv SOCK_RAW 224sockets allow sending of datagrams to correspondents 225named in 226.Xr send 2 227calls. 228Datagrams are generally received with 229.Xr recvfrom 2 , 230which returns the next datagram with its return address. 231.Pp 232An 233.Xr fcntl 2 234system call can be used to specify a process group to receive 235a 236.Dv SIGURG 237signal when the out-of-band data arrives. 238It may also enable non-blocking I/O 239and asynchronous notification of I/O events 240via 241.Dv SIGIO . 242.Pp 243The operation of sockets is controlled by socket level 244.Em options . 245These options are defined in the file 246.In sys/socket.h . 247The 248.Xr setsockopt 2 249and 250.Xr getsockopt 2 251system calls are used to set and get options, respectively. 252.Sh RETURN VALUES 253A -1 is returned if an error occurs, otherwise the return 254value is a descriptor referencing the socket. 255.Sh ERRORS 256The 257.Fn socket 258system call fails if: 259.Bl -tag -width Er 260.It Bq Er EACCES 261Permission to create a socket of the specified type and/or protocol 262is denied. 263.It Bq Er EAFNOSUPPORT 264The address family (domain) is not supported or the 265specified domain is not supported by this protocol family. 266.It Bq Er EMFILE 267The per-process descriptor table is full. 268.It Bq Er ENFILE 269The system file table is full. 270.It Bq Er ENOBUFS 271Insufficient buffer space is available. 272The socket cannot be created until sufficient resources are freed. 273.It Bq Er EPERM 274User has insufficient privileges to carry out the requested operation. 275.It Bq Er EPROTONOSUPPORT 276The protocol type or the specified protocol is not supported 277within this domain. 278.It Bq Er EPROTOTYPE 279The socket type is not supported by the protocol. 280.El 281.Sh SEE ALSO 282.Xr accept 2 , 283.Xr bind 2 , 284.Xr connect 2 , 285.Xr getpeername 2 , 286.Xr getsockname 2 , 287.Xr getsockopt 2 , 288.Xr ioctl 2 , 289.Xr listen 2 , 290.Xr read 2 , 291.Xr recv 2 , 292.Xr select 2 , 293.Xr send 2 , 294.Xr shutdown 2 , 295.Xr socketpair 2 , 296.Xr write 2 , 297.Xr getprotoent 3 , 298.Xr netgraph 4 , 299.Xr protocols 5 300.Rs 301.%T "An Introductory 4.3 BSD Interprocess Communication Tutorial" 302.%B PS1 303.%N 7 304.Re 305.Rs 306.%T "BSD Interprocess Communication Tutorial" 307.%B PS1 308.%N 8 309.Re 310.Sh HISTORY 311The 312.Fn socket 313system call appeared in 314.Bx 4.2 . 315