1.\" $NetBSD: socket.2,v 1.42 2017/05/27 21:02:55 bouyer 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. Neither the name of the University nor the names of its contributors 15.\" may be used to endorse or promote products derived from this software 16.\" without specific prior written permission. 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 19.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 20.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 21.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 22.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 23.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 24.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 25.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 26.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 27.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 28.\" SUCH DAMAGE. 29.\" 30.\" @(#)socket.2 8.1 (Berkeley) 6/4/93 31.\" 32.Dd April 27, 2017 33.Dt SOCKET 2 34.Os 35.Sh NAME 36.Nm socket 37.Nd create an endpoint for communication 38.Sh LIBRARY 39.Lb libc 40.Sh SYNOPSIS 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.Ao Pa sys/socket.h Ac . 55The currently understood formats are: 56.Pp 57.Bd -literal -offset indent -compact 58PF_LOCAL local (previously UNIX) domain protocols 59PF_INET ARPA Internet protocols 60PF_INET6 IPv6 (Internet Protocol version 6) protocols 61PF_NS Xerox Network Systems protocols 62PF_APPLETALK AppleTalk protocols 63PF_BLUETOOTH Bluetooth protocols 64PF_CAN CAN bus protocols 65.Ed 66.Pp 67The socket has the indicated 68.Fa type , 69which specifies the semantics of communication. 70Currently defined types are: 71.Pp 72.Bd -literal -offset indent -compact 73SOCK_STREAM 74SOCK_DGRAM 75SOCK_RAW 76SOCK_SEQPACKET 77SOCK_RDM 78.Ed 79.Pp 80The following flags can be or'ed to the type to condition the returned 81file descriptor: 82The following flags are valid: 83.Bl -column SOCK_NONBLOCK -offset indent 84.It Dv SOCK_CLOEXEC 85Set the close on exec property. 86.It Dv SOCK_NONBLOCK 87Sets non-blocking I/O. 88.It Dv SOCK_NOSIGPIPE 89Return 90.Er EPIPE 91instead of raising 92.Dv SIGPIPE . 93.El 94.Pp 95A 96.Dv SOCK_STREAM 97type provides sequenced, reliable, 98two-way connection based byte streams. 99An out-of-band data transmission mechanism may be supported. 100A 101.Dv SOCK_DGRAM 102socket supports 103datagrams (connectionless, unreliable messages of 104a fixed (typically small) maximum length). 105A 106.Dv SOCK_SEQPACKET 107socket may provide a sequenced, reliable, 108two-way connection-based data transmission path for datagrams 109of fixed maximum length; a consumer may be required to read 110an entire packet with each read system call. 111This facility is protocol specific, and presently implemented 112only for 113.Dv PF_NS . 114.Dv SOCK_RAW 115sockets provide access to internal network protocols and interfaces. 116The types 117.Dv SOCK_RAW , 118which is available only to the super-user, and 119.Dv SOCK_RDM , 120which is planned, 121but not yet implemented, are not described here. 122.Pp 123The 124.Fa protocol 125specifies a particular protocol to be used with the socket. 126Normally only a single protocol exists to support a particular 127socket type within a given protocol family. 128However, it is possible that many protocols may exist, in which case 129a particular protocol must be specified in this manner. 130The protocol number to use is 131particular to the \*(lqcommunication domain\*(rq in which communication 132is to take place; see 133.Xr protocols 5 . 134.Pp 135Sockets of type 136.Dv SOCK_STREAM 137are full-duplex byte streams. 138A stream socket must be in a 139.Em connected 140state before any data may be sent or received 141on it. 142A connection to another socket is created with a 143.Xr connect 2 144call. 145Once connected, data may be transferred using 146.Xr read 2 147and 148.Xr write 2 149calls or some variant of the 150.Xr send 2 151and 152.Xr recv 2 153calls. 154When a session has been completed a 155.Xr close 2 156may be performed. 157Out-of-band data may also be transmitted as described in 158.Xr send 2 159and received as described in 160.Xr recv 2 . 161.Pp 162The communications protocols used to implement a 163.Dv SOCK_STREAM 164ensure that data 165is not lost or duplicated. 166If a piece of data for which the 167peer protocol has buffer space cannot be successfully transmitted 168within a reasonable length of time, then 169the connection is considered broken and calls 170will indicate an error with 171\-1 returns and with 172.Er ETIMEDOUT 173as the specific code 174in the global variable 175.Va errno . 176The protocols optionally keep sockets 177.Dq warm 178by forcing transmissions 179roughly every minute in the absence of other activity. 180An error is then indicated if no response can be 181elicited on an otherwise 182idle connection for an extended period (e.g., 5 minutes). 183A 184.Dv SIGPIPE 185signal is raised if a process sends 186on a broken stream; this causes naive processes, 187which do not handle the signal, to exit. 188.Pp 189.Dv SOCK_SEQPACKET 190sockets employ the same system calls 191as 192.Dv SOCK_STREAM 193sockets. 194The only difference is that 195.Xr read 2 196calls will return only the amount of data requested, 197and any remaining in the arriving packet will be discarded. 198.Pp 199.Dv SOCK_DGRAM 200and 201.Dv SOCK_RAW 202sockets allow sending of datagrams to correspondents 203named in 204.Xr send 2 205calls. 206Datagrams are generally received with 207.Xr recvfrom 2 , 208which returns the next datagram with its return address. 209.Pp 210An 211.Xr fcntl 2 212call can be used to specify a process group to receive 213a 214.Dv SIGURG 215signal when the out-of-band data arrives. 216It may also enable non-blocking I/O 217and asynchronous notification of I/O events 218via 219.Dv SIGIO . 220.Pp 221The operation of sockets is controlled by socket level 222.Em options . 223These options are defined in the file 224.Ao Pa sys/socket.h Ac . 225The 226.Xr setsockopt 2 227and 228.Xr getsockopt 2 229system calls are used to set and get options, respectively. 230.Sh RETURN VALUES 231A \-1 is returned if an error occurs, otherwise the return 232value is a descriptor referencing the socket. 233.Sh ERRORS 234The 235.Fn socket 236call fails if: 237.Bl -tag -width Er 238.It Bq Er EACCES 239Permission to create a socket of the specified type and/or protocol 240is denied. 241.It Bq Er EAFNOSUPPORT 242The address family (domain) is not supported or 243the specified domain is not supported by this protocol family. 244.It Bq Er EMFILE 245The per-process descriptor table is full. 246.It Bq Er ENFILE 247The system file table is full. 248.It Bq Er ENOBUFS 249Insufficient buffer space is available. 250The socket cannot be created until sufficient resources are freed. 251.It Bq Er EPROTONOSUPPORT 252The protocol family is not supported or 253the specified protocol is not supported within this domain. 254.It Bq Er EPROTOTYPE 255The socket type is not supported by the protocol. 256.El 257.Sh SEE ALSO 258.Xr accept 2 , 259.Xr bind 2 , 260.Xr connect 2 , 261.Xr getsockname 2 , 262.Xr getsockopt 2 , 263.Xr ioctl 2 , 264.Xr listen 2 , 265.Xr poll 2 , 266.Xr read 2 , 267.Xr recv 2 , 268.Xr select 2 , 269.Xr send 2 , 270.Xr setsockopt 2 , 271.Xr shutdown 2 , 272.Xr socketpair 2 , 273.Xr write 2 , 274.Xr getprotoent 3 275.Rs 276.%T "An Introductory 4.4BSD Interprocess Communication Tutorial" 277.%A Stuart Sechrest 278.Re 279.Pq see Pa /usr/share/doc/psd/20.ipctut 280.Rs 281.%T "Advanced 4.4BSD IPC Tutorial" 282.%A Samuel J. Leffler 283.%A Robert S. Fabry 284.%A William N. Joy 285.%A Phil Lapsley 286.%A Steve Miller 287.%A Chris Torek 288.Re 289.Pq see Pa /usr/share/doc/psd/21.ipc 290.Sh HISTORY 291The 292.Fn socket 293function call appeared in 294.Bx 4.2 . 295