1.\" $NetBSD: socket.2,v 1.28 2003/08/07 16:44:09 agc 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 May 15, 2003 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 ARPA IPv6 (Internet Protocol version 6) protocols 61PF_ISO ISO protocols 62PF_NS Xerox Network Systems protocols 63PF_IMPLINK IMP \*(lqhost at IMP\*(rq link layer 64PF_APPLETALK AppleTalk 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 80A 81.Dv SOCK_STREAM 82type provides sequenced, reliable, 83two-way connection based byte streams. 84An out-of-band data transmission mechanism may be supported. 85A 86.Dv SOCK_DGRAM 87socket supports 88datagrams (connectionless, unreliable messages of 89a fixed (typically small) maximum length). 90A 91.Dv SOCK_SEQPACKET 92socket may provide a sequenced, reliable, 93two-way connection-based data transmission path for datagrams 94of fixed maximum length; a consumer may be required to read 95an entire packet with each read system call. 96This facility is protocol specific, and presently implemented 97only for 98.Dv PF_NS . 99.Dv SOCK_RAW 100sockets provide access to internal network protocols and interfaces. 101The types 102.Dv SOCK_RAW , 103which is available only to the super-user, and 104.Dv SOCK_RDM , 105which is planned, 106but not yet implemented, are not described here. 107.Pp 108The 109.Fa protocol 110specifies a particular protocol to be used with the socket. 111Normally only a single protocol exists to support a particular 112socket type within a given protocol family. 113However, it is possible that many protocols may exist, in which case 114a particular protocol must be specified in this manner. 115The protocol number to use is 116particular to the \*(lqcommunication domain\*(rq in which communication 117is to take place; see 118.Xr protocols 5 . 119.Pp 120Sockets of type 121.Dv SOCK_STREAM 122are full-duplex byte streams, similar 123to pipes. 124A stream socket must be in a 125.Em connected 126state before any data may be sent or received 127on it. 128A connection to another socket is created with a 129.Xr connect 2 130call. 131Once connected, data may be transferred using 132.Xr read 2 133and 134.Xr write 2 135calls or some variant of the 136.Xr send 2 137and 138.Xr recv 2 139calls. 140When a session has been completed a 141.Xr close 2 142may be performed. 143Out-of-band data may also be transmitted as described in 144.Xr send 2 145and received as described in 146.Xr recv 2 . 147.Pp 148The communications protocols used to implement a 149.Dv SOCK_STREAM 150ensure that data 151is not lost or duplicated. 152If a piece of data for which the 153peer protocol has buffer space cannot be successfully transmitted 154within a reasonable length of time, then 155the connection is considered broken and calls 156will indicate an error with 157-1 returns and with 158.Er ETIMEDOUT 159as the specific code 160in the global variable 161.Va errno . 162The protocols optionally keep sockets 163.Dq warm 164by forcing transmissions 165roughly every minute in the absence of other activity. 166An error is then indicated if no response can be 167elicited on an otherwise 168idle connection for an extended period (e.g., 5 minutes). 169A 170.Dv SIGPIPE 171signal is raised if a process sends 172on a broken stream; this causes naive processes, 173which do not handle the signal, to exit. 174.Pp 175.Dv SOCK_SEQPACKET 176sockets employ the same system calls 177as 178.Dv SOCK_STREAM 179sockets. 180The only difference is that 181.Xr read 2 182calls will return only the amount of data requested, 183and any remaining in the arriving packet will be discarded. 184.Pp 185.Dv SOCK_DGRAM 186and 187.Dv SOCK_RAW 188sockets allow sending of datagrams to correspondents 189named in 190.Xr send 2 191calls. 192Datagrams are generally received with 193.Xr recvfrom 2 , 194which returns the next datagram with its return address. 195.Pp 196An 197.Xr fcntl 2 198call can be used to specify a process group to receive 199a 200.Dv SIGURG 201signal when the out-of-band data arrives. 202It may also enable non-blocking I/O 203and asynchronous notification of I/O events 204via 205.Dv SIGIO . 206.Pp 207The operation of sockets is controlled by socket level 208.Em options . 209These options are defined in the file 210.Ao Pa sys/socket.h Ac . 211The 212.Xr setsockopt 2 213and 214.Xr getsockopt 2 215system calls are used to set and get options, respectively. 216.Sh RETURN VALUES 217A -1 is returned if an error occurs, otherwise the return 218value is a descriptor referencing the socket. 219.Sh ERRORS 220The 221.Fn socket 222call fails if: 223.Bl -tag -width Er 224.It Bq Er EPROTONOSUPPORT 225The protocol type or the specified protocol is not supported 226within this domain. 227.It Bq Er EMFILE 228The per-process descriptor table is full. 229.It Bq Er ENFILE 230The system file table is full. 231.It Bq Er EACCES 232Permission to create a socket of the specified type and/or protocol 233is denied. 234.It Bq Er ENOBUFS 235Insufficient buffer space is available. 236The socket cannot be created until sufficient resources are freed. 237.El 238.Sh SEE ALSO 239.Xr accept 2 , 240.Xr bind 2 , 241.Xr connect 2 , 242.Xr getsockname 2 , 243.Xr getsockopt 2 , 244.Xr ioctl 2 , 245.Xr listen 2 , 246.Xr poll 2 , 247.Xr read 2 , 248.Xr recv 2 , 249.Xr select 2 , 250.Xr send 2 , 251.Xr setsockopt 2 , 252.Xr shutdown 2 , 253.Xr socketpair 2 , 254.Xr write 2 , 255.Xr getprotoent 3 256.Rs 257.%T "An Introductory 4.4BSD Interprocess Communication Tutorial" 258.%A Stuart Sechrest 259.Re 260.Pq see Pa /usr/share/doc/psd/20.ipctut 261.Rs 262.%T "Advanced 4.4BSD IPC Tutorial" 263.%A Samuel J. Leffler 264.%A Robert S. Fabry 265.%A William N. Joy 266.%A Phil Lapsley 267.%A Steve Miller 268.%A Chris Torek 269.Re 270.Pq see Pa /usr/share/doc/psd/21.ipc 271.Sh HISTORY 272The 273.Fn socket 274function call appeared in 275.Bx 4.2 . 276