socket(3N) socket(3N)
NAME
socket - create an endpoint for communication
SYNOPSIS
cc [options] file -lsocket -lnsl
#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 ARPA Internet protocols
The socket has the indicated type, which specifies the
communication 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
transmission mechanism may be supported. A SOCK_DGRAM socket
supports 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 fixed maximum
length; a consumer may be required to read an entire packet
with each read system call. This facility is protocol
Copyright 1994 Novell, Inc. Page 1
socket(3N) socket(3N)
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 a
privileged user, and SOCK_RDM, for which no implementation
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.
However, multiple 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
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
protocol 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
connection to another socket is created with a connect call.
Once connected, data may be transferred using read and write
calls or some variant of the send and recv calls. When a
session has been completed, a close may be performed. Out-
of-band data may also be transmitted as described on the
send(3N) manual page and received as described on the recv(3N)
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 process 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 calls
will return only the amount of data requested, and any
Copyright 1994 Novell, Inc. Page 2
socket(3N) socket(3N)
remaining in the arriving packet will be discarded.
SOCK_DGRAM and SOCK_RAW sockets allow datagrams to be sent to
correspondents named in sendto calls. Datagrams are generally
received with recvfrom, which returns the next datagram with
its return address.
An fcntl 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 notification
of I/O events with SIGIO signals.
The operation of sockets is controlled by socket level
options. These options are defined in the file sys/socket.h.
setsockopt and getsockopt are used to set and get options,
respectively.
Files
/usr/lib/locale/locale/LC_MESSAGES/uxnsl
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:
EPROTONOSUPPORT The protocol type or the specified
protocol is not supported within this
domain.
EMFILE The per-process descriptor table is full.
EACCESS Permission to create a socket of the
specified type and/or protocol is denied.
ENOMEM Insufficient user memory is available.
ENOSR There were insufficient STREAMS resources
available to complete the operation.
REFERENCES
accept(3N), bind(3N), close(2), connect(3N), fcntl(2),
getsockname(3N), getsockopt(3N), ioctl(2), listen(3N),
read(2), recv(3N), send(3N), shutdown(3N), socketpair(3N),
write(2)
Copyright 1994 Novell, Inc. Page 3