Section: POSIX Programmer's Manual (3P)
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.
--- create an endpoint for communication
int socket(int domain, int type, int protocol);
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 file descriptor shall be allocated as described in
, File Descriptor Allocation.
function takes the following arguments:
Specifies the communications domain in which a socket is to be
Specifies the type of socket to be created.
Specifies a particular protocol to be used with the socket. Specifying
of 0 causes
to use an unspecified default protocol appropriate for the requested
argument specifies the address family used in the communications
domain. The address families supported by the system are
Symbolic constants that can be used for the domain argument are defined
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:
Provides sequenced, reliable, bidirectional, connection-mode byte
streams, and may provide a transmission mechanism for out-of-band
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 flag.
argument is non-zero, it shall specify a protocol that is supported by
the address family. If the
argument is zero, the default protocol for this address family and type
shall be used. The protocols supported by the system are
The process may need to have appropriate privileges to use the
function or to create some sockets.
Upon successful completion,
shall return a non-negative integer, the socket file descriptor.
Otherwise, a value of -1 shall be returned and
set to indicate the error.
function shall fail if:
The implementation does not support the specified address family.
All file descriptors available to the process are currently open.
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.
function may fail if:
The process does not have appropriate privileges.
Insufficient resources were available in the system to perform the
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
set to the protocol in question.
, File Descriptor Allocation,
The Base Definitions volume of POSIX.1-2017,
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 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
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