NAME
socket - create an endpoint for communication
SYNOPSIS
#include <sys/socket.h>
int socket(int domain, int type, int protocol);
DESCRIPTION
The socket() function shall create an unbound socket in a
communications domain, and return a file descriptor that can be used in
later function calls that operate on sockets.
The socket() function takes the following arguments:
domain Specifies the communications domain in which a socket is to be
created.
type Specifies the type of socket to be created.
protocol
Specifies a particular protocol to be used with the socket.
Specifying a protocol of 0 causes socket() to use an unspecified
default protocol appropriate for the requested socket type.
The domain argument specifies the address family used in the
communications domain. The address families supported by the system are
implementation-defined.
Symbolic constants that can be used for the domain argument are defined
in the <sys/socket.h> header.
The type argument specifies the socket type, which determines the
semantics of communication over the socket. The following socket types
are defined; implementations may specify additional socket types:
SOCK_STREAM
Provides sequenced, reliable, bidirectional, connection-mode
byte streams, and may provide a transmission mechanism for out-
of-band data.
SOCK_DGRAM
Provides datagrams, which are connectionless-mode, unreliable
messages of fixed maximum length.
SOCK_SEQPACKET
Provides sequenced, reliable, bidirectional, connection-mode
transmission paths for records. A record can be sent using one
or more output operations and received using one or more input
operations, but a single operation never transfers part of more
than one record. Record boundaries are visible to the receiver
via the MSG_EOR flag.
If the protocol argument is non-zero, it shall specify a protocol that
is supported by the address family. If the protocol argument is zero,
the default protocol for this address family and type shall be used.
The protocols supported by the system are implementation-defined.
The process may need to have appropriate privileges to use the socket()
function or to create some sockets.
RETURN VALUE
Upon successful completion, socket() shall return a non-negative
integer, the socket file descriptor. Otherwise, a value of -1 shall be
returned and errno set to indicate the error.
ERRORS
The socket() function shall fail if:
EAFNOSUPPORT
The implementation does not support the specified address
family.
EMFILE No more file descriptors are available for this process.
ENFILE No more file descriptors are available for the system.
EPROTONOSUPPORT
The protocol is not supported by the address family, or the
protocol is not supported by the implementation.
EPROTOTYPE
The socket type is not supported by the protocol.
The socket() function may fail if:
EACCES The process does not have appropriate privileges.
ENOBUFS
Insufficient resources were available in the system to perform
the operation.
ENOMEM Insufficient memory was available to fulfill the request.
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
The documentation for specific address families specifies which
protocols each address family supports. The documentation for specific
protocols specifies which socket types each protocol supports.
The application can determine whether an address family is supported by
trying to create a socket with domain set to the protocol in question.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
accept() , bind() , connect() , getsockname() , getsockopt() , listen()
, recv() , recvfrom() , recvmsg() , send() , sendmsg() , setsockopt() ,
shutdown() , socketpair() , the Base Definitions volume of
IEEE Std 1003.1-2001, <netinet/in.h>, <sys/socket.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online
at http://www.opengroup.org/unix/online.html .