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35 .\" $Id: socket.2,v 1.4 1999/05/13 11:33:42 freitag Exp $
37 .\" Modified 1993-07-24 by Rik Faith <faith@cs.unc.edu>
38 .\" Modified 1996-10-22 by Eric S. Raymond <esr@thyrsus.com>
39 .\" Modified 1998, 1999 by Andi Kleen <ak@muc.de>
40 .\" Modified 2002-07-17 by Michael Kerrisk <mtk.manpages@gmail.com>
41 .\" Modified 2004-06-17 by Michael Kerrisk <mtk.manpages@gmail.com>
43 .TH SOCKET 2 2009-01-19 "Linux" "Linux Programmer's Manual"
45 socket \- create an endpoint for communication
47 .BR "#include <sys/types.h>" " /* See NOTES */"
49 .B #include <sys/socket.h>
51 .BI "int socket(int " domain ", int " type ", int " protocol );
54 creates an endpoint for communication and returns a descriptor.
58 argument specifies a communication domain; this selects the protocol
59 family which will be used for communication.
60 These families are defined in
62 The currently understood formats include:
68 .BR AF_UNIX ", " AF_LOCAL
76 T}:IPv4 Internet protocols:T{
81 T}:IPv6 Internet protocols:T{
86 T}:IPX \- Novell protocols:
90 Kernel user interface device
96 T}:ITU-T X.25 / ISO-8208 protocol:T{
102 Amateur radio AX.25 protocol
106 T}:Access to raw ATM PVCs:
115 Low level packet interface
121 The socket has the indicated
123 which specifies the communication semantics.
124 Currently defined types
128 Provides sequenced, reliable, two-way, connection-based byte streams.
129 An out-of-band data transmission mechanism may be supported.
132 Supports datagrams (connectionless, unreliable messages of a fixed
136 Provides a sequenced, reliable, two-way connection-based data
137 transmission path for datagrams of fixed maximum length; a consumer is
138 required to read an entire packet with each input system call.
141 Provides raw network protocol access.
144 Provides a reliable datagram layer that does not guarantee ordering.
147 Obsolete and should not be used in new programs;
151 Some socket types may not be implemented by all protocol families;
154 is not implemented for
157 Since Linux 2.6.27, the
159 argument serves a second purpose:
160 in addition to specifying a socket type,
161 it may include the bitwise OR of any of the following values,
162 to modify the behavior of
168 file status flag on the new open file description.
169 Using this flag saves extra calls to
171 to achieve the same result.
174 Set the close-on-exec
176 flag on the new file descriptor.
177 See the description of the
181 for reasons why this may be useful.
185 specifies a particular protocol to be used with the socket.
186 Normally only a single protocol exists to support a particular
187 socket type within a given protocol family, in which case
189 can be specified as 0.
190 However, it is possible that many protocols may exist, in
191 which case a particular protocol must be specified in this manner.
192 The protocol number to use is specific to the \*(lqcommunication domain\*(rq
193 in which communication is to take place; see
197 on how to map protocol name strings to protocol numbers.
201 are full-duplex byte streams, similar to pipes.
204 A stream socket must be in
207 state before any data may be sent or received on it.
209 another socket is created with a
212 Once connected, data may be transferred using
216 calls or some variant of the
221 When a session has been completed a
224 Out-of-band data may also be transmitted as described in
226 and received as described in
229 The communications protocols which implement a
231 ensure that data is not lost or duplicated.
232 If a piece of data for which
233 the peer protocol has buffer space cannot be successfully transmitted
234 within a reasonable length of time, then the connection is considered
238 is enabled on the socket the protocol checks in a protocol-specific
239 manner if the other end is still alive.
242 signal is raised if a process sends or receives
243 on a broken stream; this causes naive processes,
244 which do not handle the signal, to exit.
246 sockets employ the same system calls as
249 The only difference is that
251 calls will return only the amount of data requested,
252 and any data remaining in the arriving packet will be discarded.
253 Also all message boundaries in incoming datagrams are preserved.
258 sockets allow sending of datagrams to correspondents named in
261 Datagrams are generally received with
263 which returns the next datagram along with the address of its sender.
266 is an obsolete socket type to receive raw packets directly from the
275 operation can be used to specify a process or process group to receive a
277 signal when the out-of-band data arrives or
281 connection breaks unexpectedly.
282 This operation may also be used to set the process or process group
283 that receives the I/O and asynchronous notification of I/O events via
295 When the network signals an error condition to the protocol module (e.g.,
296 using a ICMP message for IP) the pending error flag is set for the socket.
297 The next operation on this socket will return the error code of the pending
299 For some protocols it is possible to enable a per-socket error queue
300 to retrieve detailed information about the error; see
305 The operation of sockets is controlled by socket level
307 These options are defined in
313 are used to set and get options, respectively.
315 On success, a file descriptor for the new socket is returned.
316 On error, \-1 is returned, and
318 is set appropriately.
322 Permission to create a socket of the specified type and/or protocol
326 The implementation does not support the specified address family.
329 Unknown protocol, or protocol family not available.
332 .\" Since Linux 2.6.27
337 Process file table overflow.
340 The system limit on the total number of open files has been reached.
342 .BR ENOBUFS " or " ENOMEM
343 Insufficient memory is available.
345 created until sufficient resources are freed.
348 The protocol type or the specified protocol is not
349 supported within this domain.
351 Other errors may be generated by the underlying protocol modules.
353 4.4BSD, POSIX.1-2001.
359 flags are Linux-specific.
363 It is generally portable to/from
364 non-BSD systems supporting clones of the BSD socket layer (including
367 POSIX.1-2001 does not require the inclusion of
369 and this header file is not required on Linux.
370 However, some historical (BSD) implementations required this header
371 file, and portable applications are probably wise to include it.
373 The manifest constants used under 4.x BSD for protocol families
380 and so on are used for address
382 However, already the BSD man page promises: "The protocol
383 family generally is the same as the address family", and subsequent
384 standards use AF_* everywhere.
386 An example of the use of
414 \(lqAn Introductory 4.3BSD Interprocess Communication Tutorial\(rq
416 \(lqBSD Interprocess Communication Tutorial\(rq,
418 .I UNIX Programmer's Supplementary Documents Volume 1.