'\" et .TH SOCKET "3P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual" .\" .SH PROLOG 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. .\" .SH NAME socket \(em create an endpoint for communication .SH SYNOPSIS .LP .nf #include .P int socket(int \fIdomain\fP, int \fItype\fP, int \fIprotocol\fP); .fi .SH DESCRIPTION The \fIsocket\fR() 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 .IR "Section 2.14" ", " "File Descriptor Allocation". .P The \fIsocket\fR() function takes the following arguments: .IP "\fIdomain\fR" 12 Specifies the communications domain in which a socket is to be created. .IP "\fItype\fR" 12 Specifies the type of socket to be created. .IP "\fIprotocol\fR" 12 Specifies a particular protocol to be used with the socket. Specifying a .IR protocol of 0 causes \fIsocket\fR() to use an unspecified default protocol appropriate for the requested socket type. .P The .IR domain argument specifies the address family used in the communications domain. The address families supported by the system are implementation-defined. .P Symbolic constants that can be used for the domain argument are defined in the .IR header. .P The .IR 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: .IP SOCK_STREAM 12 Provides sequenced, reliable, bidirectional, connection-mode byte streams, and may provide a transmission mechanism for out-of-band data. .IP SOCK_DGRAM 12 Provides datagrams, which are connectionless-mode, unreliable messages of fixed maximum length. .IP SOCK_SEQPACKET 12 .br 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. .P If the .IR protocol argument is non-zero, it shall specify a protocol that is supported by the address family. If the .IR 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. .P The process may need to have appropriate privileges to use the \fIsocket\fR() function or to create some sockets. .SH "RETURN VALUE" Upon successful completion, \fIsocket\fR() shall return a non-negative integer, the socket file descriptor. Otherwise, a value of \-1 shall be returned and .IR errno set to indicate the error. .br .SH ERRORS The \fIsocket\fR() function shall fail if: .TP .BR EAFNOSUPPORT .br The implementation does not support the specified address family. .TP .BR EMFILE All file descriptors available to the process are currently open. .TP .BR ENFILE No more file descriptors are available for the system. .TP .BR EPROTONOSUPPORT .br The protocol is not supported by the address family, or the protocol is not supported by the implementation. .TP .BR EPROTOTYPE The socket type is not supported by the protocol. .P The \fIsocket\fR() function may fail if: .TP .BR EACCES The process does not have appropriate privileges. .TP .BR ENOBUFS Insufficient resources were available in the system to perform the operation. .TP .BR ENOMEM Insufficient memory was available to fulfill the request. .LP .IR "The following sections are informative." .SH "EXAMPLES" None. .SH "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. .P The application can determine whether an address family is supported by trying to create a socket with .IR domain set to the protocol in question. .SH "RATIONALE" None. .SH "FUTURE DIRECTIONS" None. .SH "SEE ALSO" .IR "Section 2.14" ", " "File Descriptor Allocation", .IR "\fIaccept\fR\^(\|)", .IR "\fIbind\fR\^(\|)", .IR "\fIconnect\fR\^(\|)", .IR "\fIgetsockname\fR\^(\|)", .IR "\fIgetsockopt\fR\^(\|)", .IR "\fIlisten\fR\^(\|)", .IR "\fIrecv\fR\^(\|)", .IR "\fIrecvfrom\fR\^(\|)", .IR "\fIrecvmsg\fR\^(\|)", .IR "\fIsend\fR\^(\|)", .IR "\fIsendmsg\fR\^(\|)", .IR "\fIsetsockopt\fR\^(\|)", .IR "\fIshutdown\fR\^(\|)", .IR "\fIsocketpair\fR\^(\|)" .P The Base Definitions volume of POSIX.1\(hy2017, .IR "\fB\fP", .IR "\fB\fP" .\" .SH COPYRIGHT 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 . .PP 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 .