.\" Copyright (c) 1983 The Regents of the University of California.
.\" Redistribution and use in source and binary forms are permitted
.\" provided that the above copyright notice and this paragraph are
.\" duplicated in all such forms and that any documentation,
.\" advertising materials, and other materials related to such
.\" distribution and use acknowledge that the software was developed
.\" by the University of California, Berkeley. The name of the
.\" University may not be used to endorse or promote products derived
.\" from this software without specific prior written permission.
.\" THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
.\" IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
.\" WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
.\" @(#)socket.2 6.6 (Berkeley) %G%
socket \- create an endpoint for communication
s = socket(domain, type, protocol)
int s, domain, type, protocol;
creates an endpoint for communication and returns a descriptor.
parameter specifies a communications domain within which
communication will take place; this selects the protocol family
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
The currently understood formats are
PF_UNIX (UNIX internal protocols),
PF_INET (ARPA Internet protocols),
PF_NS (Xerox Network Systems protocols), and
PF_IMPLINK (IMP \*(lqhost at IMP\*(rq link layer).
The socket has the indicated
which specifies the semantics of communication. Currently
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 specific, and presently implemented
SOCK_RAW sockets provide access to internal network protocols and interfaces.
which is available only to the super-user, and
SOCK_RDM, which is planned,
but not yet implemented, are not described here.
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, it is possible
that 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 \*(lqcommunication domain\*(rq in which communication
Sockets of type SOCK_STREAM
are full-duplex byte streams, similar
to pipes. A stream socket must be in a
state before any data may be sent or received
on it. A connection to another socket is created with a
call. Once connected, data may be transferred using
calls or some variant of the
calls. When a session has been completed a
Out-of-band data may also be transmitted as described in
and received as described in
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 \*(lqwarm\*(rq by
roughly every minute in the absence of other activity.
An error is then indicated if no response can be
idle connection for a extended period (e.g. 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
calls will return only the amount of data requested,
and any remaining in the arriving packet will be discarded.
sockets allow sending of datagrams to correspondents
calls. Datagrams are generally received with
which returns the next datagram with its return address.
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
The operation of sockets is controlled by socket level
These options are defined in the file
are used to set and get options, respectively.
A \-1 is returned if an error occurs, otherwise the return
value is a descriptor referencing the socket.
The \fIsocket\fP call fails if:
The protocol type or the specified protocol is not supported
The per-process descriptor table is full.
The system file table is full.
Permission to create a socket of the specified type and/or protocol
Insufficient buffer space is available.
The socket cannot be created until sufficient resources are freed.
accept(2), bind(2), connect(2), getsockname(2), getsockopt(2),
ioctl(2), listen(2), read(2), recv(2),
select(2), send(2), shutdown(2), socketpair(2), write(2)
``An Introductory 4.3BSD Interprocess Communication Tutorial.''
(reprinted in UNIX Programmer's Supplementary Documents Volume 1, PS1:7)
``An Advanced 4.3BSD Interprocess Communication Tutorial.''
(reprinted in UNIX Programmer's Supplementary Documents Volume 1, PS1:8)