Sockets Library Functions socket(3SOCKET)

NAME

socket - create an endpoint for communication

SYNOPSIS

cc [ flag ... ] file ... -lsocket -lnsl [ library ... ]

#include <sys/types.h>

#include <sys/socket.h>

int socket(int domain, int type, int protocol);

DESCRIPTION

socket() creates an endpoint for communication and returns a

descriptor.

The domain parameter specifies a communications domain

within which communication will take place; this selects the

protocol family which should be used. The protocol family

generally is the same as the address family for the

addresses supplied in later operations on the socket. These

families are defined in the include file <sys/socket.h>.

There must be an entry in the netconfig(4) file for at least

each protocol family and type required. If protocol has

been specified, but no exact match for the tuplet family,

type, protocol is found, then the first entry containing the

specified family and type with zero for protocol will be

used. The currently understood formats are:

PF_UNIX

UNIX system internal protocols

PF_INET

Internet Protocol Version 4 (IPv4)

PF_INET6

Internet Protocol Version 6 (IPv6)

The socket has the indicated type, which specifies the com-

munication semantics. Currently defined types are:

SOCK_STREAM

SOCK_DGRAM

SOCK_RAW

SOCK_SEQPACKET

SOCK_RDM

A SOCK_STREAM type provides sequenced, reliable, two-way

connection-based byte streams. An out-of-band data transmis-

sion mechanism may be supported. A SOCK_DGRAM socket sup-

ports datagrams (connectionless, unreliable messages of a

fixed (typically small) maximum length). A SOCK_SEQPACKET

socket may provide a sequenced, reliable, two-way

connection-based data transmission path for datagrams of

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Sockets Library Functions socket(3SOCKET)

fixed maximum length; a consumer may be required to read an

entire packet with each read system call. This facility is

protocol specific, and presently not implemented for any

protocol family. SOCK_RAW sockets provide access to internal

network interfaces. The types SOCK_RAW, which is available

only to the superuser, and SOCK_RDM, for which no implemen-

tation currently exists, are not described here.

protocol specifies a particular protocol to be used with the

socket. Normally only a single protocol exists to support a

particular socket type within a given protocol family. How-

ever, multiple protocols may exist, in which case a particu-

lar protocol must be specified in this manner. The protocol

number to use is particular to the "communication domain" in

which communication is to take place. If a protocol is

specified by the caller, then it will be packaged into a

socket level option request and sent to the underlying pro-

tocol layers.

Sockets of type SOCK_STREAM are full-duplex byte streams,

similar to pipes. A stream socket must be in a connected

state before any data may be sent or received on it. A con-

nection to another socket is created with a connect(3SOCKET)

call. Once connected, data may be transferred using read(2)

and write(2) calls or some variant of the send(3SOCKET) and

recv(3SOCKET) calls. When a session has been completed, a

close(2) may be performed. Out-of-band data may also be

transmitted as described on the send(3SOCKET) manual page

and received as described on the recv(3SOCKET) manual page.

The communications protocols used to implement a SOCK_STREAM

insure 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,

then the connection is considered broken and calls will

indicate an error with -1 returns and with ETIMEDOUT as the

specific code in the global variable errno. The protocols

optionally keep sockets "warm" by forcing transmissions

roughly every minute in the absence of other activity. An

error is then indicated if no response can be elicited on an

otherwise idle connection for a extended period (for

instance 5 minutes). A SIGPIPE signal is raised if a pro-

cess sends on a broken stream; this causes naive processes,

which do not handle the signal, to exit.

SOCK_SEQPACKET sockets employ the same system calls as

SOCK_STREAM sockets. The only difference is that read(2)

calls will return only the amount of data requested, and any

remaining in the arriving packet will be discarded.

SOCK_DGRAM and SOCK_RAW sockets allow datagrams to be sent

to correspondents named in sendto(3SOCKET) calls. Datagrams

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Sockets Library Functions socket(3SOCKET)

are generally received with recvfrom(3SOCKET), which returns

the next datagram with its return address.

An fcntl(2) call can be used to specify a process group to

receive a SIGURG signal when the out-of-band data arrives.

It may also enable non-blocking I/O and asynchronous notifi-

cation of I/O events with SIGIO signals.

. These options are defined in the file

<sys/ssocket.h>.

The operation of sockets is controlled by socket level

options. setsockopt(3SOCKET) and getsockopt(3SOCKET)

are used to set and get options, respectively.

RETURN VALUES

A -1 is returned if an error occurs. Otherwise the return

value is a descriptor referencing the socket.

ERRORS

The socket() call fails if:

EACCES

Permission to create a socket of the specified type

and/or protocol is denied.

EMFILE

The per-process descriptor table is full.

ENOMEM

Insufficient user memory is available.

ENOSR There were insufficient STREAMS resources available to

complete the operation.

EPROTONOSUPPORT

The protocol type or the specified protocol is not

supported within this domain.

ATTRIBUTES

See attributes(5) for descriptions of the following attri-

butes:

____________________________________________________________

| ATTRIBUTE TYPE | ATTRIBUTE VALUE |

|______________________________|______________________________|

| MT-Level | Safe |

|______________________________|______________________________|