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32.\" From: @(#)socket.2 8.1 (Berkeley) 6/4/93
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33.\" $FreeBSD: head/lib/libc/sys/socket.2 108028 2002-12-18 09:22:32Z ru $
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| 33.\" $FreeBSD: head/lib/libc/sys/socket.2 108087 2002-12-19 09:40:28Z ru $ |
34.\"
35.Dd November 24, 1997
36.Dt SOCKET 2
37.Os
38.Sh NAME
39.Nm socket
40.Nd create an endpoint for communication
41.Sh LIBRARY
42.Lb libc
43.Sh SYNOPSIS
44.In sys/types.h
45.In sys/socket.h
46.Ft int
47.Fn socket "int domain" "int type" "int protocol"
48.Sh DESCRIPTION
49The
50.Fn socket
51system call
52creates an endpoint for communication and returns a descriptor.
53.Pp
54The
55.Fa domain
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56parameter specifies a communications domain within which
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| 56argument specifies a communications domain within which |
57communication will take place; this selects the protocol family
58which should be used.
59These families are defined in the include file
60.Ao Pa sys/socket.h Ac .
61The currently understood formats are:
62.Pp
63.Bd -literal -offset indent -compact
64PF_LOCAL Host-internal protocols, formerly called PF_UNIX,
65PF_UNIX Host-internal protocols, deprecated, use PF_LOCAL,
66PF_INET Internet version 4 protocols,
67PF_IMPLINK ARPAnet IMP addresses,
68PF_PUP PUP protocols, like BSP,
69PF_CHAOS MIT CHAOS protocols,
70PF_NS Xerox Network Systems protocols,
71PF_ISO ISO protocols,
72PF_OSI Open Systems Interconnection protocols,
73PF_ECMA European Computer Manufacturers,
74PF_DATAKIT Datakit protocols,
75PF_CCITT ITU-T protocols, like X.25,
76PF_SNA IBM SNA,
77PF_DECnet DECnet,
78PF_DLI DEC Direct Data Link Interface protocol,
79PF_LAT LAT protocol,
80PF_HYLINK NSC Hyperchannel,
81PF_APPLETALK AppleTalk protocols,
82PF_ROUTE Internal Routing protocol,
83PF_LINK Link layer interface,
84PF_XTP eXpress Transfer Protocol,
85PF_COIP Connection-Oriented IP, aka ST II,
86PF_CNT Computer Network Technology,
87PF_SIP Simple Internet Protocol,
88PF_IPX Novell Intenet Packet eXchange protocol,
89PF_RTIP Help Identify RTIP packets,
90PF_PIP Help Identify PIP packets,
91PF_ISDN Integrated Services Digital Network,
92PF_KEY Internal key-management function,
93PF_INET6 Internet version 6 protocols,
94PF_NATM Native ATM access,
95PF_ATM ATM,
96PF_NETGRAPH Netgraph sockets
97.Ed
98.Pp
99The socket has the indicated
100.Fa type ,
101which specifies the semantics of communication. Currently
102defined types are:
103.Pp
104.Bd -literal -offset indent -compact
105SOCK_STREAM Stream socket,
106SOCK_DGRAM Datagram socket,
107SOCK_RAW Raw-protocol interface,
108SOCK_RDM Reliably-delivered packet,
109SOCK_SEQPACKET Sequenced packet stream
110.Ed
111.Pp
112A
113.Dv SOCK_STREAM
114type provides sequenced, reliable,
115two-way connection based byte streams.
116An out-of-band data transmission mechanism may be supported.
117A
118.Dv SOCK_DGRAM
119socket supports
120datagrams (connectionless, unreliable messages of
121a fixed (typically small) maximum length).
122A
123.Dv SOCK_SEQPACKET
124socket may provide a sequenced, reliable,
125two-way connection-based data transmission path for datagrams
126of fixed maximum length; a consumer may be required to read
127an entire packet with each read system call.
128This facility is protocol specific, and presently implemented
129only for
130.Dv PF_NS .
131.Dv SOCK_RAW
132sockets provide access to internal network protocols and interfaces.
133The types
134.Dv SOCK_RAW ,
135which is available only to the super-user, and
136.Dv SOCK_RDM ,
137which is planned,
138but not yet implemented, are not described here.
139.Pp
140The
141.Fa protocol
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| 142argument |
143specifies a particular protocol to be used with the socket.
144Normally only a single protocol exists to support a particular
145socket type within a given protocol family. However, it is possible
146that many protocols may exist, in which case a particular protocol
147must be specified in this manner. The protocol number to use is
148particular to the
149.Dq "communication domain"
150in which communication
151is to take place; see
152.Xr protocols 5 .
153.Pp
154Sockets of type
155.Dv SOCK_STREAM
156are full-duplex byte streams, similar
157to pipes. A stream socket must be in a
158.Em connected
159state before any data may be sent or received
160on it. A connection to another socket is created with a
161.Xr connect 2
162system call.
163Once connected, data may be transferred using
164.Xr read 2
165and
166.Xr write 2
167calls or some variant of the
168.Xr send 2
169and
170.Xr recv 2
171functions.
172(Some protocol families, such as the Internet family,
173support the notion of an
174.Dq implied connect ,
175which permits data to be sent piggybacked onto a connect operation by
176using the
177.Xr sendto 2
178system call.)
179When a session has been completed a
180.Xr close 2
181may be performed.
182Out-of-band data may also be transmitted as described in
183.Xr send 2
184and received as described in
185.Xr recv 2 .
186.Pp
187The communications protocols used to implement a
188.Dv SOCK_STREAM
189insure that data
190is not lost or duplicated. If a piece of data for which the
191peer protocol has buffer space cannot be successfully transmitted
192within a reasonable length of time, then
193the connection is considered broken and calls
194will indicate an error with
195-1 returns and with
196.Er ETIMEDOUT
197as the specific code
198in the global variable
199.Va errno .
200The protocols optionally keep sockets
201.Dq warm
202by forcing transmissions
203roughly every minute in the absence of other activity.
204An error is then indicated if no response can be
205elicited on an otherwise
206idle connection for a extended period (e.g. 5 minutes).
207A
208.Dv SIGPIPE
209signal is raised if a process sends
210on a broken stream; this causes naive processes,
211which do not handle the signal, to exit.
212.Pp
213.Dv SOCK_SEQPACKET
214sockets employ the same system calls
215as
216.Dv SOCK_STREAM
217sockets. The only difference
218is that
219.Xr read 2
220calls will return only the amount of data requested,
221and any remaining in the arriving packet will be discarded.
222.Pp
223.Dv SOCK_DGRAM
224and
225.Dv SOCK_RAW
226sockets allow sending of datagrams to correspondents
227named in
228.Xr send 2
229calls. Datagrams are generally received with
230.Xr recvfrom 2 ,
231which returns the next datagram with its return address.
232.Pp
233An
234.Xr fcntl 2
235system call can be used to specify a process group to receive
236a
237.Dv SIGURG
238signal when the out-of-band data arrives.
239It may also enable non-blocking I/O
240and asynchronous notification of I/O events
241via
242.Dv SIGIO .
243.Pp
244The operation of sockets is controlled by socket level
245.Em options .
246These options are defined in the file
247.Ao Pa sys/socket.h Ac .
248.Xr Setsockopt 2
249and
250.Xr getsockopt 2
251are used to set and get options, respectively.
252.Sh RETURN VALUES
253A -1 is returned if an error occurs, otherwise the return
254value is a descriptor referencing the socket.
255.Sh ERRORS
256The
257.Fn socket
258system call fails if:
259.Bl -tag -width Er
260.It Bq Er EPROTONOSUPPORT
261The protocol type or the specified protocol is not supported
262within this domain.
263.It Bq Er EMFILE
264The per-process descriptor table is full.
265.It Bq Er ENFILE
266The system file table is full.
267.It Bq Er EACCES
268Permission to create a socket of the specified type and/or protocol
269is denied.
270.It Bq Er ENOBUFS
271Insufficient buffer space is available.
272The socket cannot be created until sufficient resources are freed.
273.El
274.Sh SEE ALSO
275.Xr accept 2 ,
276.Xr bind 2 ,
277.Xr connect 2 ,
278.Xr getpeername 2 ,
279.Xr getsockname 2 ,
280.Xr getsockopt 2 ,
281.Xr ioctl 2 ,
282.Xr listen 2 ,
283.Xr read 2 ,
284.Xr recv 2 ,
285.Xr select 2 ,
286.Xr send 2 ,
287.Xr shutdown 2 ,
288.Xr socketpair 2 ,
289.Xr write 2 ,
290.Xr getprotoent 3 ,
291.Xr netgraph 4 ,
292.Xr protocols 5
293.Rs
294.%T "An Introductory 4.3 BSD Interprocess Communication Tutorial"
295.%B PS1
296.%N 7
297.Re
298.Rs
299.%T "BSD Interprocess Communication Tutorial"
300.%B PS1
301.%N 8
302.Re
303.Sh HISTORY
304The
305.Fn socket
306system call appeared in
307.Bx 4.2 .
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