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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 $
36 .Nd create an endpoint for communication
43 .Fn socket "int domain" "int type" "int protocol"
46 creates an endpoint for communication and returns a descriptor.
50 parameter specifies a communications domain within which
51 communication will take place; this selects the protocol family
53 These families are defined in the include file
55 The currently understood formats are:
57 .Bd -literal -offset indent -compact
58 PF_LOCAL Host-internal protocols, formerly called PF_UNIX,
59 PF_UNIX Host-internal protocols, deprecated, use PF_LOCAL,
60 PF_INET Internet version 4 protocols,
61 PF_IMPLINK ARPAnet IMP addresses,
62 PF_PUP PUP protocols, like BSP,
63 PF_CHAOS MIT CHAOS protocols,
64 PF_NS Xerox Network Systems protocols,
66 PF_OSI Open Systems Interconnection protocols,
67 PF_ECMA European Computer Manufacturers,
68 PF_DATAKIT Datakit protocols,
69 PF_CCITT ITU-T protocols, like X.25,
72 PF_DLI DEC Direct Data Link Interface protocol,
74 PF_HYLINK NSC Hyperchannel,
75 PF_ROUTE Internal Routing protocol,
76 PF_LINK Link layer interface,
77 PF_XTP eXpress Transfer Protocol,
78 PF_COIP Connection-Oriented IP, aka ST II,
79 PF_CNT Computer Network Technology,
80 PF_SIP Simple Internet Protocol,
81 PF_IPX Novell Internet Packet eXchange protocol,
82 PF_RTIP Help Identify RTIP packets,
83 PF_PIP Help Identify PIP packets,
84 PF_ISDN Integrated Services Digital Network,
85 PF_KEY Internal key-management function,
86 PF_INET6 Internet version 6 protocols,
87 PF_NATM Native ATM access,
89 PF_NETGRAPH Netgraph sockets
92 The socket has the indicated
94 which specifies the semantics of communication. Currently
97 .Bd -literal -offset indent -compact
98 SOCK_STREAM Stream socket,
99 SOCK_DGRAM Datagram socket,
100 SOCK_RAW Raw-protocol interface,
101 SOCK_RDM Reliably-delivered packet,
102 SOCK_SEQPACKET Sequenced packet stream
107 type provides sequenced, reliable,
108 two-way connection based byte streams.
109 An out-of-band data transmission mechanism may be supported.
113 datagrams (connectionless, unreliable messages of
114 a fixed (typically small) maximum length).
117 socket may provide a sequenced, reliable,
118 two-way connection-based data transmission path for datagrams
119 of fixed maximum length; a consumer may be required to read
120 an entire packet with each read system call.
121 This facility is protocol specific, and presently implemented
127 sockets provide access to internal network protocols and interfaces.
130 which is available only to the super-user, and
133 but not yet implemented, are not described here.
135 Additionally, the following flags are allowed in the
139 .Bd -literal -offset indent -compact
140 SOCK_CLOEXEC Set close-on-exec on the new descriptor,
141 SOCK_NONBLOCK Set non-blocking mode on the new socket
146 specifies a particular protocol to be used with the socket.
147 Normally only a single protocol exists to support a particular
148 socket type within a given protocol family. However, it is possible
149 that many protocols may exist, in which case a particular protocol
150 must be specified in this manner. The protocol number to use is
152 .Dq "communication domain"
153 in which communication
154 is to take place; see
159 are full-duplex byte streams, similar
160 to pipes. A stream socket must be in a
162 state before any data may be sent or received
163 on it. A connection to another socket is created with a
166 Once connected, data may be transferred using
170 calls or some variant of the
175 (Some protocol families, such as the Internet family,
176 support the notion of an
177 .Dq implied connect ,
178 which permits data to be sent piggybacked onto a connect operation by
182 When a session has been completed a
185 Out-of-band data may also be transmitted as described in
187 and received as described in
190 The communications protocols used to implement a
193 is not lost or duplicated. If a piece of data for which the
194 peer protocol has buffer space cannot be successfully transmitted
195 within a reasonable length of time, then
196 the connection is considered broken and calls
197 will indicate an error with
201 in the global variable
203 The protocols optionally keep sockets
205 by forcing transmissions
206 roughly every minute in the absence of other activity.
207 An error is then indicated if no response can be
208 elicited on an otherwise
209 idle connection for an extended period (e.g. 5 minutes).
212 signal is raised if a process sends
213 on a broken stream; this causes naive processes,
214 which do not handle the signal, to exit.
217 sockets employ the same system calls
220 sockets. The only difference
223 calls will return only the amount of data requested,
224 and any remaining in the arriving packet will be discarded.
229 sockets allow sending of datagrams to correspondents
232 calls. Datagrams are generally received with
234 which returns the next datagram with its return address.
238 call can be used to specify a process group to receive
241 signal when the out-of-band data arrives.
242 It may also enable non-blocking I/O
243 and asynchronous notification of I/O events
247 The operation of sockets is controlled by socket level
249 These options are defined in the file
254 are used to set and get options, respectively.
256 Upon successful completion
258 returns a descriptor referencing the socket.
259 Otherwise, -1 is returned and the global variable
261 is set to indicate the error.
267 .It Bq Er EPROTONOSUPPORT
268 The protocol type or the specified protocol is not supported
271 The per-process descriptor table is full.
273 The system file table is full.
275 Permission to create a socket of the specified type and/or protocol
278 Insufficient buffer space is available.
279 The socket cannot be created until sufficient resources are freed.
301 .%T "An Introductory 4.3 BSD Interprocess Communication Tutorial"
306 .%T "BSD Interprocess Communication Tutorial"
313 function call appeared in