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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.
118 Additionally, the following flags are allowed in the
122 .Bd -literal -offset indent -compact
123 SOCK_CLOEXEC Set close-on-exec on the new descriptor,
124 SOCK_NONBLOCK Set non-blocking mode on the new socket
130 specifies a particular protocol to be used with the socket.
131 Normally only a single protocol exists to support a particular
132 socket type within a given protocol family.
133 However, it is possible
134 that many protocols may exist, in which case a particular protocol
135 must be specified in this manner.
136 The protocol number to use is
138 .Dq "communication domain"
139 in which communication
140 is to take place; see
145 argument may be set to zero (0) to request the default
146 implementation of a socket type for the protocol, if any.
150 are full-duplex byte streams, similar
152 A stream socket must be in a
154 state before any data may be sent or received
156 A connection to another socket is created with a
159 Once connected, data may be transferred using
163 calls or some variant of the
168 (Some protocol families, such as the Internet family,
169 support the notion of an
170 .Dq implied connect ,
171 which permits data to be sent piggybacked onto a connect operation by
175 When a session has been completed a
178 Out-of-band data may also be transmitted as described in
180 and received as described in
183 The communications protocols used to implement a
186 is not lost or duplicated.
187 If a piece of data for which the
188 peer protocol has buffer space cannot be successfully transmitted
189 within a reasonable length of time, then
190 the connection is considered broken and calls
191 will indicate an error with
195 in the global variable
197 The protocols optionally keep sockets
199 by forcing transmissions
200 roughly every minute in the absence of other activity.
201 An error is then indicated if no response can be
202 elicited on an otherwise
203 idle connection for an extended period (e.g.\& 5 minutes).
206 signal is raised if a process sends
207 on a broken stream, but this behavior may be inhibited via
211 sockets employ the same system calls
218 calls will return only the amount of data requested,
219 and any remaining in the arriving packet will be discarded.
224 sockets allow sending of datagrams to correspondents
228 Datagrams are generally received with
230 which returns the next datagram with its return address.
234 system call can be used to specify a process group to receive
237 signal when the out-of-band data arrives.
238 It may also enable non-blocking I/O
239 and asynchronous notification of I/O events
243 The operation of sockets is controlled by socket level
245 These options are defined in the file
251 system calls are used to set and get options, respectively.
253 A -1 is returned if an error occurs, otherwise the return
254 value is a descriptor referencing the socket.
258 system call fails if:
261 Permission to create a socket of the specified type and/or protocol
263 .It Bq Er EAFNOSUPPORT
264 The address family (domain) is not supported or the
265 specified domain is not supported by this protocol family.
267 The per-process descriptor table is full.
269 The system file table is full.
271 Insufficient buffer space is available.
272 The socket cannot be created until sufficient resources are freed.
274 User has insufficient privileges to carry out the requested operation.
275 .It Bq Er EPROTONOSUPPORT
276 The protocol type or the specified protocol is not supported
279 The socket type is not supported by the protocol.
301 .%T "An Introductory 4.3 BSD Interprocess Communication Tutorial"
306 .%T "BSD Interprocess Communication Tutorial"
313 system call appeared in