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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: src/lib/libc/sys/socket.2,v 1.12.2.11 2002/12/29 16:35:34 schweikh Exp $ 30.\" 31.Dd November 24, 1997 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 45.Fn Socket 46creates an endpoint for communication and returns a descriptor. 47.Pp 48The 49.Fa domain 50parameter specifies a communications domain within which 51communication will take place; this selects the protocol family 52which should be used. 53These families are defined in the include file 54.In sys/socket.h . 55The currently understood formats are: 56.Pp 57.Bd -literal -offset indent -compact 58PF_LOCAL Host-internal protocols, formerly called PF_UNIX, 59PF_UNIX Host-internal protocols, deprecated, use PF_LOCAL, 60PF_INET Internet version 4 protocols, 61PF_IMPLINK ARPAnet IMP addresses, 62PF_PUP PUP protocols, like BSP, 63PF_CHAOS MIT CHAOS protocols, 64PF_NS Xerox Network Systems protocols, 65PF_ISO ISO protocols, 66PF_OSI Open Systems Interconnection protocols, 67PF_ECMA European Computer Manufacturers, 68PF_DATAKIT Datakit protocols, 69PF_CCITT ITU-T protocols, like X.25, 70PF_SNA IBM SNA, 71PF_DECnet DECnet, 72PF_DLI DEC Direct Data Link Interface protocol, 73PF_LAT LAT protocol, 74PF_HYLINK NSC Hyperchannel, 75PF_ROUTE Internal Routing protocol, 76PF_LINK Link layer interface, 77PF_XTP eXpress Transfer Protocol, 78PF_COIP Connection-Oriented IP, aka ST II, 79PF_CNT Computer Network Technology, 80PF_SIP Simple Internet Protocol, 81PF_IPX Novell Internet Packet eXchange protocol, 82PF_RTIP Help Identify RTIP packets, 83PF_PIP Help Identify PIP packets, 84PF_ISDN Integrated Services Digital Network, 85PF_KEY Internal key-management function, 86PF_INET6 Internet version 6 protocols, 87PF_NATM Native ATM access, 88PF_ATM ATM, 89PF_NETGRAPH Netgraph sockets 90.Ed 91.Pp 92The socket has the indicated 93.Fa type , 94which specifies the semantics of communication. Currently 95defined types are: 96.Pp 97.Bd -literal -offset indent -compact 98SOCK_STREAM Stream socket, 99SOCK_DGRAM Datagram socket, 100SOCK_RAW Raw-protocol interface, 101SOCK_RDM Reliably-delivered packet, 102SOCK_SEQPACKET Sequenced packet stream 103.Ed 104.Pp 105A 106.Dv SOCK_STREAM 107type provides sequenced, reliable, 108two-way connection based byte streams. 109An out-of-band data transmission mechanism may be supported. 110A 111.Dv SOCK_DGRAM 112socket supports 113datagrams (connectionless, unreliable messages of 114a fixed (typically small) maximum length). 115A 116.Dv SOCK_SEQPACKET 117socket may provide a sequenced, reliable, 118two-way connection-based data transmission path for datagrams 119of fixed maximum length; a consumer may be required to read 120an entire packet with each read system call. 121This facility is protocol specific, and presently implemented 122only for 123.Dv PF_NS 124and 125.Dv PF_UNIX . 126.Dv SOCK_RAW 127sockets provide access to internal network protocols and interfaces. 128The types 129.Dv SOCK_RAW , 130which is available only to the super-user, and 131.Dv SOCK_RDM , 132which is planned, 133but not yet implemented, are not described here. 134.Pp 135The 136.Fa protocol 137specifies a particular protocol to be used with the socket. 138Normally only a single protocol exists to support a particular 139socket type within a given protocol family. However, it is possible 140that many protocols may exist, in which case a particular protocol 141must be specified in this manner. The protocol number to use is 142particular to the 143.Dq "communication domain" 144in which communication 145is to take place; see 146.Xr protocols 5 . 147.Pp 148Sockets of type 149.Dv SOCK_STREAM 150are full-duplex byte streams, similar 151to pipes. A stream socket must be in a 152.Em connected 153state before any data may be sent or received 154on it. A connection to another socket is created with a 155.Xr connect 2 156call. 157Once connected, data may be transferred using 158.Xr read 2 159and 160.Xr write 2 161calls or some variant of the 162.Xr send 2 163and 164.Xr recv 2 165calls. 166(Some protocol families, such as the Internet family, 167support the notion of an 168.Dq implied connect , 169which permits data to be sent piggybacked onto a connect operation by 170using the 171.Xr sendto 2 172call.) 173When a session has been completed a 174.Xr close 2 175may be performed. 176Out-of-band data may also be transmitted as described in 177.Xr send 2 178and received as described in 179.Xr recv 2 . 180.Pp 181The communications protocols used to implement a 182.Dv SOCK_STREAM 183insure that data 184is not lost or duplicated. If a piece of data for which the 185peer protocol has buffer space cannot be successfully transmitted 186within a reasonable length of time, then 187the connection is considered broken and calls 188will indicate an error with 189-1 returns and with 190.Er ETIMEDOUT 191as the specific code 192in the global variable 193.Va errno . 194The protocols optionally keep sockets 195.Dq warm 196by forcing transmissions 197roughly every minute in the absence of other activity. 198An error is then indicated if no response can be 199elicited on an otherwise 200idle connection for an extended period (e.g. 5 minutes). 201A 202.Dv SIGPIPE 203signal is raised if a process sends 204on a broken stream; this causes naive processes, 205which do not handle the signal, to exit. 206.Pp 207.Dv SOCK_SEQPACKET 208sockets employ the same system calls 209as 210.Dv SOCK_STREAM 211sockets. The only difference 212is that 213.Xr read 2 214calls will return only the amount of data requested, 215and any remaining in the arriving packet will be discarded. 216.Pp 217.Dv SOCK_DGRAM 218and 219.Dv SOCK_RAW 220sockets allow sending of datagrams to correspondents 221named in 222.Xr send 2 223calls. Datagrams are generally received with 224.Xr recvfrom 2 , 225which returns the next datagram with its return address. 226.Pp 227An 228.Xr fcntl 2 229call can be used to specify a process group to receive 230a 231.Dv SIGURG 232signal when the out-of-band data arrives. 233It may also enable non-blocking I/O 234and asynchronous notification of I/O events 235via 236.Dv SIGIO . 237.Pp 238The operation of sockets is controlled by socket level 239.Em options . 240These options are defined in the file 241.In sys/socket.h . 242.Xr Setsockopt 2 243and 244.Xr getsockopt 2 245are used to set and get options, respectively. 246.Sh RETURN VALUES 247Upon successful completion 248.Fn socket 249returns a descriptor referencing the socket. 250Otherwise, -1 is returned and the global variable 251.Va errno 252is set to indicate the error. 253.Sh ERRORS 254The 255.Fn socket 256call fails if: 257.Bl -tag -width Er 258.It Bq Er EPROTONOSUPPORT 259The protocol type or the specified protocol is not supported 260within this domain. 261.It Bq Er EMFILE 262The per-process descriptor table is full. 263.It Bq Er ENFILE 264The system file table is full. 265.It Bq Er EACCES 266Permission to create a socket of the specified type and/or protocol 267is denied. 268.It Bq Er ENOBUFS 269Insufficient buffer space is available. 270The socket cannot be created until sufficient resources are freed. 271.El 272.Sh SEE ALSO 273.Xr accept 2 , 274.Xr bind 2 , 275.Xr connect 2 , 276.Xr getpeername 2 , 277.Xr getsockname 2 , 278.Xr getsockopt 2 , 279.Xr ioctl 2 , 280.Xr listen 2 , 281.Xr read 2 , 282.Xr recv 2 , 283.Xr select 2 , 284.Xr send 2 , 285.Xr shutdown 2 , 286.Xr socketpair 2 , 287.Xr write 2 , 288.Xr getprotoent 3 , 289.Xr netgraph 4 , 290.Xr protocols 5 291.Rs 292.%T "An Introductory 4.3 BSD Interprocess Communication Tutorial" 293.%B PS1 294.%N 7 295.Re 296.Rs 297.%T "BSD Interprocess Communication Tutorial" 298.%B PS1 299.%N 8 300.Re 301.Sh HISTORY 302The 303.Fn socket 304function call appeared in 305.Bx 4.2 . 306