1130b656e5
This will make a number of things easier in the future, as well as (finally!) avoiding the Id-smashing problem which has plagued developers for so long. Boy, I'm glad we're not using sup anymore. This update would have been insane otherwise.
271 lines
7.8 KiB
Groff
271 lines
7.8 KiB
Groff
.\" Copyright (c) 1983, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" From: @(#)socket.2 8.1 (Berkeley) 6/4/93
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.\" $FreeBSD$
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.\"
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.Dd February 15, 1995
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.Dt SOCKET 2
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.Os BSD 4.2
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.Sh NAME
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.Nm socket
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.Nd create an endpoint for communication
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.Sh SYNOPSIS
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.Fd #include <sys/types.h>
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.Fd #include <sys/socket.h>
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.Ft int
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.Fn socket "int domain" "int type" "int protocol"
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.Sh DESCRIPTION
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.Fn Socket
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creates an endpoint for communication and returns a descriptor.
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.Pp
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The
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.Fa domain
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parameter specifies a communications domain within which
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communication will take place; this selects the protocol family
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which should be used.
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These families are defined in the include file
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.Ao Pa sys/socket.h Ac .
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The currently understood formats are
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.Pp
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.Bd -literal -offset indent -compact
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PF_LOCAL (Host-internal protocols, formerly called PF_UNIX),
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PF_INET (ARPA Internet protocols),
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PF_ISO (ISO protocols),
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PF_CCITT (ITU-T protocols, like X.25),
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PF_NS (Xerox Network Systems protocols), and
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.\"PF_IMPLINK (IMP \*(lqhost at IMP\*(rq link layer).
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.Ed
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.Pp
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The socket has the indicated
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.Fa type ,
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which specifies the semantics of communication. Currently
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defined types are:
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.Pp
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.Bd -literal -offset indent -compact
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SOCK_STREAM
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SOCK_DGRAM
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SOCK_RAW
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SOCK_SEQPACKET
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SOCK_RDM
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.Ed
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.Pp
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A
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.Dv SOCK_STREAM
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type provides sequenced, reliable,
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two-way connection based byte streams.
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An out-of-band data transmission mechanism may be supported.
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A
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.Dv SOCK_DGRAM
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socket supports
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datagrams (connectionless, unreliable messages of
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a fixed (typically small) maximum length).
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A
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.Dv SOCK_SEQPACKET
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socket may provide a sequenced, reliable,
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two-way connection-based data transmission path for datagrams
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of fixed maximum length; a consumer may be required to read
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an entire packet with each read system call.
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This facility is protocol specific, and presently implemented
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only for
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.Dv PF_NS .
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.Dv SOCK_RAW
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sockets provide access to internal network protocols and interfaces.
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The types
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.Dv SOCK_RAW ,
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which is available only to the super-user, and
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.Dv SOCK_RDM ,
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which is planned,
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but not yet implemented, are not described here.
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.Pp
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The
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.Fa protocol
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specifies a particular protocol to be used with the socket.
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Normally only a single protocol exists to support a particular
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socket type within a given protocol family. However, it is possible
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that many protocols may exist, in which case a particular protocol
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must be specified in this manner. The protocol number to use is
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particular to the \*(lqcommunication domain\*(rq in which communication
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is to take place; see
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.Xr protocols 5 .
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.Pp
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Sockets of type
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.Dv SOCK_STREAM
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are full-duplex byte streams, similar
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to pipes. A stream socket must be in a
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.Em connected
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state before any data may be sent or received
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on it. A connection to another socket is created with a
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.Xr connect 2
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call.
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Once connected, data may be transferred using
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.Xr read 2
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and
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.Xr write 2
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calls or some variant of the
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.Xr send 2
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and
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.Xr recv 2
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calls.
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(Some protocol families, such as the Internet family,
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support the notion of an
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.Dq implied connect,
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which permits data to be sent piggybacked onto a connect operation by
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using the
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.Xr sendto 2
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call.)
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When a session has been completed a
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.Xr close 2
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may be performed.
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Out-of-band data may also be transmitted as described in
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.Xr send 2
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and received as described in
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.Xr recv 2 .
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.Pp
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The communications protocols used to implement a
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.Dv SOCK_STREAM
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insure that data
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is not lost or duplicated. If a piece of data for which the
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peer protocol has buffer space cannot be successfully transmitted
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within a reasonable length of time, then
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the connection is considered broken and calls
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will indicate an error with
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-1 returns and with
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.Dv ETIMEDOUT
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as the specific code
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in the global variable
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.Va errno .
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The protocols optionally keep sockets
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.Dq warm
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by forcing transmissions
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roughly every minute in the absence of other activity.
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An error is then indicated if no response can be
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elicited on an otherwise
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idle connection for a extended period (e.g. 5 minutes).
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A
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.Dv SIGPIPE
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signal is raised if a process sends
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on a broken stream; this causes naive processes,
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which do not handle the signal, to exit.
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.Pp
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.Dv SOCK_SEQPACKET
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sockets employ the same system calls
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as
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.Dv SOCK_STREAM
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sockets. The only difference
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is that
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.Xr read 2
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calls will return only the amount of data requested,
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and any remaining in the arriving packet will be discarded.
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.Pp
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.Dv SOCK_DGRAM
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and
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.Dv SOCK_RAW
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sockets allow sending of datagrams to correspondents
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named in
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.Xr send 2
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calls. Datagrams are generally received with
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.Xr recvfrom 2 ,
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which returns the next datagram with its return address.
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.Pp
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An
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.Xr fcntl 2
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call can be used to specify a process group to receive
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a
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.Dv SIGURG
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signal when the out-of-band data arrives.
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It may also enable non-blocking I/O
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and asynchronous notification of I/O events
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via
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.Dv SIGIO .
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.Pp
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The operation of sockets is controlled by socket level
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.Em options .
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These options are defined in the file
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.Ao Pa sys/socket.h Ac .
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.Xr Setsockopt 2
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and
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.Xr getsockopt 2
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are used to set and get options, respectively.
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.Sh RETURN VALUES
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A -1 is returned if an error occurs, otherwise the return
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value is a descriptor referencing the socket.
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.Sh ERRORS
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The
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.Fn socket
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call fails if:
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.Bl -tag -width EPROTONOPSUPPORTA
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.It Bq Er EPROTONOSUPPORT
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The protocol type or the specified protocol is not supported
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within this domain.
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.It Bq Er EMFILE
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The per-process descriptor table is full.
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.It Bq Er ENFILE
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The system file table is full.
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.It Bq Er EACCESS
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Permission to create a socket of the specified type and/or protocol
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is denied.
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.It Bq Er ENOBUFS
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Insufficient buffer space is available.
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The socket cannot be created until sufficient resources are freed.
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.El
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.Sh SEE ALSO
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.Xr accept 2 ,
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.Xr bind 2 ,
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.Xr connect 2 ,
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.Xr getprotoent 3 ,
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.Xr getsockname 2 ,
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.Xr getsockopt 2 ,
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.Xr ioctl 2 ,
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.Xr listen 2 ,
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.Xr read 2 ,
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.Xr recv 2 ,
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.Xr select 2 ,
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.Xr send 2 ,
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.Xr shutdown 2 ,
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.Xr socketpair 2 ,
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.Xr write 2
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.Rs
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.%T "An Introductory 4.3 BSD Interprocess Communication Tutorial"
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.%B PS1
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.%N 7
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.Re
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.Rs
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.%T "BSD Interprocess Communication Tutorial"
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.%B PS1
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.%N 8
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.Re
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.Sh HISTORY
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The
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.Fn socket
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function call appeared in
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.Bx 4.2 .
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