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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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SOCKET(3P) POSIX Programmer's Manual SOCKET(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.
socket — create an endpoint for communication
#include <sys/socket.h>
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 file
descriptor shall be allocated as described in Section 2.14, File
Descriptor Allocation.
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.
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.
The socket() function shall fail if:
EAFNOSUPPORT
The implementation does not support the specified address
family.
EMFILE All file descriptors available to the process are currently
open.
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.
None.
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.
None.
None.
Section 2.14, File Descriptor Allocation, accept(3p), bind(3p),
connect(3p), getsockname(3p), getsockopt(3p), listen(3p),
recv(3p), recvfrom(3p), recvmsg(3p), send(3p), sendmsg(3p),
setsockopt(3p), shutdown(3p), socketpair(3p)
The Base Definitions volume of POSIX.1‐2017, netinet_in.h(0p),
sys_socket.h(0p)
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
http://www.opengroup.org/unix/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
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2017 SOCKET(3P)
Pages that refer to this page: sys_socket.h(0p), sys_un.h(0p), accept(3p), bind(3p), connect(3p), fdopen(3p), freeaddrinfo(3p), getnameinfo(3p), getpeername(3p), getsockname(3p), getsockopt(3p), listen(3p), recv(3p), recvfrom(3p), recvmsg(3p), send(3p), sendmsg(3p), sendto(3p), setsockopt(3p), shutdown(3p), socketpair(3p)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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