# socket

## 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.
    


## NAME



           socket — create an endpoint for communication
    


## SYNOPSIS



           #include <sys/socket.h>
    
           int socket(int _domain_ , int _type_ , int _protocol_);
    


## DESCRIPTION



           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.
    


## RETURN VALUE



           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.
    


## ERRORS



           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._
    


## EXAMPLES



           None.
    


## 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.
    
           The application can determine whether an address family is
           supported by trying to create a socket with _domain_ set to the
           protocol in question.
    


## RATIONALE



           None.
    


## FUTURE DIRECTIONS



           None.
    


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