NAME

socket − create an endpoint for communication

USAGE

#include <sys/types.h>
#include <sys/socket.h>

s = socket(af, type, protocol)
int s, af, type, protocol;

DESCRIPTION

Socket creates an endpoint for communication and returns a descriptor. 

The af parameter specifies an address format in which addresses specified by later operations at the socket should be interpreted.  These formats are defined in the include file <sys/socket.h>.  The only currently available format is:

AF_INET(ARPA Internet addresses),

The socket has the indicated type which specifies the semantics of communication.  Possible types are:

SOCK_STREAM
SOCK_DGRAM

A SOCK_STREAM type provides sequenced, reliable, two-way connection-based byte streams with an out-of-band data transmission mechanism.  A SOCK_DGRAM socket supports datagrams (i.e., connectionless, unreliable messages of a fixed (typically small) maximum length). 

The protocol specifies a particular protocol to be used with the socket.  Normally, only a single protocol exists to support a particular socket type using a given address format.  However, many protocols may exist, in which case a particular protocol must be specified in this manner.  The protocol number to use is particular to the “communication environment” in which communication is to take place; see services(5) and protocols(5). 

Sockets of the type SOCK_STREAM are full-duplex byte streams, similar to pipes.  A stream socket must be connected before any data can be sent or received on it.  A connection to another socket is created with a connect(2) call.  Once connected, data may be transferred using read(2) and write(2) calls or some variant of the send(2) and recv(2) calls.  When a session is over, a close(2) is performed.  Out-of-band data may also be transmitted as described in send(2) and received as described in recv(2). 

The communications protocols used to implement a SOCK_STREAM ensure that data is not lost or duplicated.  If a piece of data for which the peer protocol has buffer space cannot be successfully transmitted within a reasonable length of time, the connection is considered broken and calls will indicate an error with a return of −1 and with ETIMEDOUT as the specific code in the global variable errno.  The protocols may keep sockets active by forcing transmissions roughly every minute in the absence of other activity.  An error is indicated if no response can be elicited on an otherwise idle connection for a extended time period (e.g., 5 minutes).  A SIGPIPE signal is raised if a process sends on a broken stream; this causes processes which do not handle the signal to exit. 

SOCK_DGRAM sockets allow the sending of datagrams to correspondents named in send(2) calls.  You may receive datagrams at such a socket with recv(2). 

An fcntl(2) call can be used to specify a process group that will receive a SIGURG signal when the out-of-band data arrives. 

RETURN VALUE

A −1 is returned if an error occurs; otherwise, the return value is a descriptor referencing the socket. 

ERRORS

The socket call fails if:

[EAFNOSUPPORT] The specified address family is not supported in this version of the system. 

[ESOCKTNOSUPPORT]
The specified socket type is not supported in this address family.

[EPROTONOSUPPORT]
The specified protocol is not supported.

[EMFILE] The per-process descriptor table is full. 

[ENOBUFS] No buffer space is available.  The socket cannot be created. 

RELATED INFORMATION

accept(2), bind(2), connect(2), getsockname(2), getsockopt(2), ioctl(2), listen(2), recv(2), select(2), send(2), shutdown(2), socketpair(2)