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28 .\" From: @(#)socket.2 8.1 (Berkeley) 6/4/93
36 .Nd create an endpoint for communication
43 .Fn socket "int domain" "int type" "int protocol"
48 creates an endpoint for communication and returns a descriptor.
52 argument specifies a communications domain within which
53 communication will take place; this selects the protocol family
55 These families are defined in the include file
57 The currently understood formats are:
59 .Bd -literal -offset indent -compact
60 PF_LOCAL Host-internal protocols, formerly called PF_UNIX,
61 PF_UNIX Host-internal protocols, deprecated, use PF_LOCAL,
62 PF_INET Internet version 4 protocols,
63 PF_PUP PUP protocols, like BSP,
64 PF_APPLETALK AppleTalk protocols,
65 PF_ROUTE Internal Routing protocol,
66 PF_LINK Link layer interface,
67 PF_IPX Novell Internet Packet eXchange protocol,
68 PF_RTIP Help Identify RTIP packets,
69 PF_PIP Help Identify PIP packets,
70 PF_ISDN Integrated Services Digital Network,
71 PF_KEY Internal key-management function,
72 PF_INET6 Internet version 6 protocols,
73 PF_NATM Native ATM access,
75 PF_NETGRAPH Netgraph sockets
78 The socket has the indicated
80 which specifies the semantics of communication.
84 .Bd -literal -offset indent -compact
85 SOCK_STREAM Stream socket,
86 SOCK_DGRAM Datagram socket,
87 SOCK_RAW Raw-protocol interface,
88 SOCK_RDM Reliably-delivered packet,
89 SOCK_SEQPACKET Sequenced packet stream
94 type provides sequenced, reliable,
95 two-way connection based byte streams.
96 An out-of-band data transmission mechanism may be supported.
100 datagrams (connectionless, unreliable messages of
101 a fixed (typically small) maximum length).
104 socket may provide a sequenced, reliable,
105 two-way connection-based data transmission path for datagrams
106 of fixed maximum length; a consumer may be required to read
107 an entire packet with each read system call.
108 This facility is protocol specific, and presently unimplemented.
110 sockets provide access to internal network protocols and interfaces.
113 which is available only to the super-user, and
116 but not yet implemented, are not described here.
121 specifies a particular protocol to be used with the socket.
122 Normally only a single protocol exists to support a particular
123 socket type within a given protocol family.
124 However, it is possible
125 that many protocols may exist, in which case a particular protocol
126 must be specified in this manner.
127 The protocol number to use is
129 .Dq "communication domain"
130 in which communication
131 is to take place; see
136 argument may be set to zero (0) to request the default
137 implementation of a socket type for the protocol, if any.
141 are full-duplex byte streams, similar
143 A stream socket must be in a
145 state before any data may be sent or received
147 A connection to another socket is created with a
150 Once connected, data may be transferred using
154 calls or some variant of the
159 (Some protocol families, such as the Internet family,
160 support the notion of an
161 .Dq implied connect ,
162 which permits data to be sent piggybacked onto a connect operation by
166 When a session has been completed a
169 Out-of-band data may also be transmitted as described in
171 and received as described in
174 The communications protocols used to implement a
177 is not lost or duplicated.
178 If a piece of data for which the
179 peer protocol has buffer space cannot be successfully transmitted
180 within a reasonable length of time, then
181 the connection is considered broken and calls
182 will indicate an error with
186 in the global variable
188 The protocols optionally keep sockets
190 by forcing transmissions
191 roughly every minute in the absence of other activity.
192 An error is then indicated if no response can be
193 elicited on an otherwise
194 idle connection for an extended period (e.g.\& 5 minutes).
197 signal is raised if a process sends
198 on a broken stream, but this behavior may be inhibited via
202 sockets employ the same system calls
209 calls will return only the amount of data requested,
210 and any remaining in the arriving packet will be discarded.
215 sockets allow sending of datagrams to correspondents
219 Datagrams are generally received with
221 which returns the next datagram with its return address.
225 system call can be used to specify a process group to receive
228 signal when the out-of-band data arrives.
229 It may also enable non-blocking I/O
230 and asynchronous notification of I/O events
234 The operation of sockets is controlled by socket level
236 These options are defined in the file
242 system calls are used to set and get options, respectively.
244 A -1 is returned if an error occurs, otherwise the return
245 value is a descriptor referencing the socket.
249 system call fails if:
251 .It Bq Er EPROTONOSUPPORT
252 The protocol type or the specified protocol is not supported
255 The per-process descriptor table is full.
257 The system file table is full.
259 Permission to create a socket of the specified type and/or protocol
262 Insufficient buffer space is available.
263 The socket cannot be created until sufficient resources are freed.
265 User has insufficient privileges to carry out the requested operation.
287 .%T "An Introductory 4.3 BSD Interprocess Communication Tutorial"
292 .%T "BSD Interprocess Communication Tutorial"
299 system call appeared in