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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 2013-12-31 "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.
153 Since Linux 2.6.27, the
155 argument serves a second purpose:
156 in addition to specifying a socket type,
157 it may include the bitwise OR of any of the following values,
158 to modify the behavior of
164 file status flag on the new open file description.
165 Using this flag saves extra calls to
167 to achieve the same result.
170 Set the close-on-exec
172 flag on the new file descriptor.
173 See the description of the
177 for reasons why this may be useful.
181 specifies a particular protocol to be used with the socket.
182 Normally only a single protocol exists to support a particular
183 socket type within a given protocol family, in which case
185 can be specified as 0.
186 However, it is possible that many protocols may exist, in
187 which case a particular protocol must be specified in this manner.
188 The protocol number to use is specific to the \*(lqcommunication domain\*(rq
189 in which communication is to take place; see
193 on how to map protocol name strings to protocol numbers.
197 are full-duplex byte streams, similar to pipes.
200 A stream socket must be in
203 state before any data may be sent or received on it.
205 another socket is created with a
208 Once connected, data may be transferred using
212 calls or some variant of the
217 When a session has been completed a
220 Out-of-band data may also be transmitted as described in
222 and received as described in
225 The communications protocols which implement a
227 ensure that data is not lost or duplicated.
228 If a piece of data for which
229 the peer protocol has buffer space cannot be successfully transmitted
230 within a reasonable length of time, then the connection is considered
234 is enabled on the socket the protocol checks in a protocol-specific
235 manner if the other end is still alive.
238 signal is raised if a process sends or receives
239 on a broken stream; this causes naive processes,
240 which do not handle the signal, to exit.
242 sockets employ the same system calls as
245 The only difference is that
247 calls will return only the amount of data requested,
248 and any data remaining in the arriving packet will be discarded.
249 Also all message boundaries in incoming datagrams are preserved.
254 sockets allow sending of datagrams to correspondents named in
257 Datagrams are generally received with
259 which returns the next datagram along with the address of its sender.
262 is an obsolete socket type to receive raw packets directly from the
271 operation can be used to specify a process or process group to receive a
273 signal when the out-of-band data arrives or
277 connection breaks unexpectedly.
278 This operation may also be used to set the process or process group
279 that receives the I/O and asynchronous notification of I/O events via
291 When the network signals an error condition to the protocol module (e.g.,
292 using a ICMP message for IP) the pending error flag is set for the socket.
293 The next operation on this socket will return the error code of the pending
295 For some protocols it is possible to enable a per-socket error queue
296 to retrieve detailed information about the error; see
301 The operation of sockets is controlled by socket level
303 These options are defined in
309 are used to set and get options, respectively.
311 On success, a file descriptor for the new socket is returned.
312 On error, \-1 is returned, and
314 is set appropriately.
318 Permission to create a socket of the specified type and/or protocol
322 The implementation does not support the specified address family.
325 Unknown protocol, or protocol family not available.
328 .\" Since Linux 2.6.27
333 Process file table overflow.
336 The system limit on the total number of open files has been reached.
338 .BR ENOBUFS " or " ENOMEM
339 Insufficient memory is available.
341 created until sufficient resources are freed.
344 The protocol type or the specified protocol is not
345 supported within this domain.
347 Other errors may be generated by the underlying protocol modules.
349 4.4BSD, POSIX.1-2001.
355 flags are Linux-specific.
359 It is generally portable to/from
360 non-BSD systems supporting clones of the BSD socket layer (including
363 POSIX.1-2001 does not require the inclusion of
365 and this header file is not required on Linux.
366 However, some historical (BSD) implementations required this header
367 file, and portable applications are probably wise to include it.
369 The manifest constants used under 4.x BSD for protocol families
376 and so on are used for address
378 However, already the BSD man page promises: "The protocol
379 family generally is the same as the address family", and subsequent
380 standards use AF_* everywhere.
382 An example of the use of
410 \(lqAn Introductory 4.3BSD Interprocess Communication Tutorial\(rq
412 \(lqBSD Interprocess Communication Tutorial\(rq,
414 .I UNIX Programmer's Supplementary Documents Volume 1.
416 This page is part of release 3.67 of the Linux
419 A description of the project,
420 information about reporting bugs,
421 and the latest version of this page,
423 \%http://www.kernel.org/doc/man\-pages/.