SOCKET(P) POSIX Programmer's Manual SOCKET(P)
socket - create an endpoint for communication
int socket(int domain, int type, int protocol);
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.
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
The type argument specifies the socket type, which determines the semantics of communica-
tion over the socket. The following socket types are defined; implementations may specify
additional socket types:
Provides sequenced, reliable, bidirectional, connection-mode byte streams, and may
provide a transmission mechanism for out-of-band data.
Provides datagrams, which are connectionless-mode, unreliable messages of fixed
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
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-
The process may need to have appropriate privileges to use the socket() function or to
create some sockets.
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
The socket() function shall fail if:
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.
The protocol is not supported by the address family, or the protocol is not sup-
ported by the implementation.
The socket type is not supported by the protocol.
The socket() function may fail if:
EACCES The process does not have appropriate privileges.
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.
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.
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>
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 orig-
inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 SOCKET(P)