This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior), or
the interface may not be implemented on Linux.
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
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
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.
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.
The socket() function shall fail if:
The implementation does not support the specified address
EMFILE All file descriptors available to the process are currently
ENFILE No more file descriptors are available for the system.
The protocol is not supported by the address family, or the
protocol is not supported 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
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
The application can determine whether an address family is supported
by trying to create a socket with domain set to the protocol in
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The Open
Group Base Specifications Issue 7, Copyright (C) 2013 by the
Institute of Electrical and Electronics Engineers, Inc and The Open
Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
applied.) 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.unix.org/online.html .
Any typographical or formatting errors that appear in this page are
most likely to have been introduced during the conversion of the
source files to man page format. To report such errors, see
IEEE/The Open Group 2013 SOCKET(3P)