.\" $OpenBSD: socket.2,v 1.18 2000/10/18 05:12:12 aaron Exp $
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.\" $OpenBSD: socket.2,v 1.18 2000/10/18 05:12:12 aaron Exp $
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.\" $NetBSD: socket.2,v 1.5 1995/02/27 12:37:53 cgd Exp $
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.\" $NetBSD: socket.2,v 1.5 1995/02/27 12:37:53 cgd Exp $
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.\"
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.\"
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.\" Copyright (c) 1983, 1991, 1993
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.\" Copyright (c) 1983, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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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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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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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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.\" 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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.\" 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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.\" 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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.\" 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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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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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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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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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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.\" 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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.\" 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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.\" without specific prior written permission.
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.\"
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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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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.\" 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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.\" 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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.\" 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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.\" 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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.\" 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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.\" 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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.\" 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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.\" 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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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\" SUCH DAMAGE.
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.\"
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.\"
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.\" @(#)socket.2 8.1 (Berkeley) 6/4/93
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.\" @(#)socket.2 8.1 (Berkeley) 6/4/93
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.\"
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.\"
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.Dd June 4, 1993
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.Dd June 4, 1993
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.Dt SOCKET 2
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.Dt SOCKET 2
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.Os
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.Os
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.Sh NAME
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.Sh NAME
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.Nm socket
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.Nm socket
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.Nd create an endpoint for communication
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.Nd create an endpoint for communication
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.Sh SYNOPSIS
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.Sh SYNOPSIS
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.Fd #include
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.Fd #include
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.Fd #include
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.Fd #include
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.Ft int
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.Ft int
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.Fn socket "int domain" "int type" "int protocol"
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.Fn socket "int domain" "int type" "int protocol"
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.Sh DESCRIPTION
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.Sh DESCRIPTION
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.Fn socket
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.Fn socket
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creates an endpoint for communication and returns a descriptor.
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creates an endpoint for communication and returns a descriptor.
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.Pp
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.Pp
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The
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The
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.Fa domain
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.Fa domain
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parameter specifies a communications domain within which
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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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communication will take place; this selects the protocol family
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which should be used.
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which should be used.
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These families are defined in the include file
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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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.Ao Pa sys/socket.h Ac .
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The currently understood formats are
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The currently understood formats are
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.Pp
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.Pp
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.Bd -literal -offset indent -compact
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.Bd -literal -offset indent -compact
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AF_UNIX (UNIX internal protocols),
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AF_UNIX (UNIX internal protocols),
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AF_INET (ARPA Internet protocols),
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AF_INET (ARPA Internet protocols),
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AF_INET6 (ARPA IPv6 protocols),
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AF_INET6 (ARPA IPv6 protocols),
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AF_ISO (ISO protocols),
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AF_ISO (ISO protocols),
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AF_NS (Xerox Network Systems protocols),
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AF_NS (Xerox Network Systems protocols),
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AF_IPX (Internetwork Packet Exchange), and
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AF_IPX (Internetwork Packet Exchange), and
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AF_IMPLINK (IMP \*(lqhost at IMP\*(rq link layer).
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AF_IMPLINK (IMP \*(lqhost at IMP\*(rq link layer).
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.Ed
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.Ed
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.Pp
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.Pp
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The socket has the indicated
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The socket has the indicated
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.Fa type ,
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.Fa type ,
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which specifies the semantics of communication.
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which specifies the semantics of communication.
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Currently defined types are:
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Currently defined types are:
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.Pp
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.Pp
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.Bd -literal -offset indent -compact
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.Bd -literal -offset indent -compact
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SOCK_STREAM
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SOCK_STREAM
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SOCK_DGRAM
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SOCK_DGRAM
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SOCK_RAW
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SOCK_RAW
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SOCK_SEQPACKET
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SOCK_SEQPACKET
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SOCK_RDM
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SOCK_RDM
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.Ed
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.Ed
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.Pp
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.Pp
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A
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A
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.Dv SOCK_STREAM
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.Dv SOCK_STREAM
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type provides sequenced, reliable,
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type provides sequenced, reliable,
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two-way connection based byte streams.
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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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An out-of-band data transmission mechanism may be supported.
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A
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A
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.Dv SOCK_DGRAM
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.Dv SOCK_DGRAM
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socket supports
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socket supports
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datagrams (connectionless, unreliable messages of
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datagrams (connectionless, unreliable messages of
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a fixed (typically small) maximum length).
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a fixed (typically small) maximum length).
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A
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A
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.Dv SOCK_SEQPACKET
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.Dv SOCK_SEQPACKET
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socket may provide a sequenced, reliable,
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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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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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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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an entire packet with each read system call.
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This facility is protocol specific, and presently implemented
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This facility is protocol specific, and presently implemented
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only for
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only for
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.Dv PF_NS .
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.Dv PF_NS .
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.Dv SOCK_RAW
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.Dv SOCK_RAW
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sockets provide access to internal network protocols and interfaces.
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sockets provide access to internal network protocols and interfaces.
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The types
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The types
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.Dv SOCK_RAW ,
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.Dv SOCK_RAW ,
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which is available only to the superuser, and
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which is available only to the superuser, and
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.Dv SOCK_RDM ,
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.Dv SOCK_RDM ,
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which is planned,
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which is planned,
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but not yet implemented, are not described here.
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but not yet implemented, are not described here.
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.Pp
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.Pp
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The
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The
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.Fa protocol
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.Fa protocol
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specifies a particular protocol to be used with the socket.
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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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Normally only a single protocol exists to support a particular
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socket type within a given protocol family.
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socket type within a given protocol family.
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However, it is possible that many protocols may exist,
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However, it is possible that many protocols may exist,
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in which case a particular protocol must be specified in this manner.
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in which case a particular protocol must be specified in this manner.
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The protocol number to use is particular to the \*(lqcommunication domain\*(rq
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The protocol number to use is particular to the \*(lqcommunication domain\*(rq
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in which communication is to take place; see
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in which communication is to take place; see
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.Xr protocols 5 .
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.Xr protocols 5 .
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A value of 0 for
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A value of 0 for
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.Fa protocol
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.Fa protocol
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will let the system select an appropriate protocol for the requested
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will let the system select an appropriate protocol for the requested
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socket type.
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socket type.
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.Pp
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.Pp
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Sockets of type
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Sockets of type
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.Dv SOCK_STREAM
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.Dv SOCK_STREAM
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are full-duplex byte streams, similar to pipes.
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are full-duplex byte streams, similar to pipes.
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A stream socket must be in a
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A stream socket must be in a
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.Em connected
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.Em connected
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state before any data may be sent or received on it.
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state before any data may be sent or received on it.
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A connection to another socket is created with a
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A connection to another socket is created with a
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.Xr connect 2
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.Xr connect 2
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call.
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call.
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Once connected, data may be transferred using
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Once connected, data may be transferred using
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.Xr read 2
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.Xr read 2
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and
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and
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.Xr write 2
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.Xr write 2
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calls or some variant of the
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calls or some variant of the
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.Xr send 2
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.Xr send 2
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and
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and
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.Xr recv 2
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.Xr recv 2
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calls.
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calls.
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When a session has been completed a
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When a session has been completed a
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.Xr close 2
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.Xr close 2
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may be performed.
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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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Out-of-band data may also be transmitted as described in
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.Xr send 2
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.Xr send 2
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and received as described in
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and received as described in
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.Xr recv 2 .
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.Xr recv 2 .
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.Pp
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.Pp
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The communications protocols used to implement a
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The communications protocols used to implement a
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.Dv SOCK_STREAM
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.Dv SOCK_STREAM
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ensure that data is not lost or duplicated.
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ensure that data is not lost or duplicated.
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If a piece of data for which the peer protocol has buffer space cannot
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If a piece of data for which the peer protocol has buffer space cannot
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be successfully transmitted within a reasonable length of time, then the
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be successfully transmitted within a reasonable length of time, then the
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connection is considered broken and calls will indicate an error with \-1
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connection is considered broken and calls will indicate an error with \-1
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returns and with
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returns and with
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.Er ETIMEDOUT
|
.Er ETIMEDOUT
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as the specific code in the global variable
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as the specific code in the global variable
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.Va errno .
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.Va errno .
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The protocols optionally keep sockets
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The protocols optionally keep sockets
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.Dq warm
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.Dq warm
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by forcing transmissions roughly every minute in the absence of other activity.
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by forcing transmissions roughly every minute in the absence of other activity.
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An error is then indicated if no response can be elicited on an otherwise
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An error is then indicated if no response can be elicited on an otherwise
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idle connection for a extended period (e.g., 5 minutes).
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idle connection for a extended period (e.g., 5 minutes).
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A
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A
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.Dv SIGPIPE
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.Dv SIGPIPE
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signal is raised if a process sends on a broken stream; this causes
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signal is raised if a process sends on a broken stream; this causes
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naive processes, which do not handle the signal, to exit.
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naive processes, which do not handle the signal, to exit.
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.Pp
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.Pp
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.Dv SOCK_SEQPACKET
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.Dv SOCK_SEQPACKET
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sockets employ the same system calls
|
sockets employ the same system calls
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as
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as
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.Dv SOCK_STREAM
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.Dv SOCK_STREAM
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sockets.
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sockets.
|
The only difference is that
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The only difference is that
|
.Xr read 2
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.Xr read 2
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calls will return only the amount of data requested,
|
calls will return only the amount of data requested,
|
and any remaining in the arriving packet will be discarded.
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and any remaining in the arriving packet will be discarded.
|
.Pp
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.Pp
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.Dv SOCK_DGRAM
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.Dv SOCK_DGRAM
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and
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and
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.Dv SOCK_RAW
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.Dv SOCK_RAW
|
sockets allow sending of datagrams to correspondents named in
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sockets allow sending of datagrams to correspondents named in
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.Xr send 2
|
.Xr send 2
|
calls.
|
calls.
|
Datagrams are generally received with
|
Datagrams are generally received with
|
.Xr recvfrom 2 ,
|
.Xr recvfrom 2 ,
|
which returns the next datagram with its return address.
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which returns the next datagram with its return address.
|
.Pp
|
.Pp
|
An
|
An
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.Xr fcntl 2
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.Xr fcntl 2
|
call can be used to specify a process group to receive
|
call can be used to specify a process group to receive
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a
|
a
|
.Dv SIGURG
|
.Dv SIGURG
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signal when the out-of-band data arrives.
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signal when the out-of-band data arrives.
|
It may also enable non-blocking I/O and asynchronous notification
|
It may also enable non-blocking I/O and asynchronous notification
|
of I/O events via
|
of I/O events via
|
.Dv SIGIO .
|
.Dv SIGIO .
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.Pp
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.Pp
|
The operation of sockets is controlled by socket level
|
The operation of sockets is controlled by socket level
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.Em options .
|
.Em options .
|
These options are defined in the file
|
These options are defined in the file
|
.Ao Pa sys/socket.h Ac .
|
.Ao Pa sys/socket.h Ac .
|
.Xr setsockopt 2
|
.Xr setsockopt 2
|
and
|
and
|
.Xr getsockopt 2
|
.Xr getsockopt 2
|
are used to set and get options, respectively.
|
are used to set and get options, respectively.
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.Sh RETURN VALUES
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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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A \-1 is returned if an error occurs, otherwise the return
|
value is a descriptor referencing the socket.
|
value is a descriptor referencing the socket.
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.Sh ERRORS
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.Sh ERRORS
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The
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The
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.Fn socket
|
.Fn socket
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call fails if:
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call fails if:
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.Bl -tag -width Er
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.Bl -tag -width Er
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.It Bq Er EPROTONOSUPPORT
|
.It Bq Er EPROTONOSUPPORT
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The protocol type or the specified protocol is not supported
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The protocol type or the specified protocol is not supported
|
within this domain.
|
within this domain.
|
.It Bq Er EMFILE
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.It Bq Er EMFILE
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The per-process descriptor table is full.
|
The per-process descriptor table is full.
|
.It Bq Er ENFILE
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.It Bq Er ENFILE
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The system file table is full.
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The system file table is full.
|
.It Bq Er EACCES
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.It Bq Er EACCES
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Permission to create a socket of the specified type and/or protocol
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Permission to create a socket of the specified type and/or protocol
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is denied.
|
is denied.
|
.It Bq Er ENOBUFS
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.It Bq Er ENOBUFS
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Insufficient buffer space is available.
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Insufficient buffer space is available.
|
The socket cannot be created until sufficient resources are freed.
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The socket cannot be created until sufficient resources are freed.
|
.El
|
.El
|
.Sh SEE ALSO
|
.Sh SEE ALSO
|
.Xr accept 2 ,
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.Xr accept 2 ,
|
.Xr bind 2 ,
|
.Xr bind 2 ,
|
.Xr connect 2 ,
|
.Xr connect 2 ,
|
.Xr getsockname 2 ,
|
.Xr getsockname 2 ,
|
.Xr getsockopt 2 ,
|
.Xr getsockopt 2 ,
|
.Xr ioctl 2 ,
|
.Xr ioctl 2 ,
|
.Xr listen 2 ,
|
.Xr listen 2 ,
|
.Xr poll 2 ,
|
.Xr poll 2 ,
|
.Xr read 2 ,
|
.Xr read 2 ,
|
.Xr recv 2 ,
|
.Xr recv 2 ,
|
.Xr select 2 ,
|
.Xr select 2 ,
|
.Xr send 2 ,
|
.Xr send 2 ,
|
.Xr setsockopt 2 ,
|
.Xr setsockopt 2 ,
|
.Xr shutdown 2 ,
|
.Xr shutdown 2 ,
|
.Xr socketpair 2 ,
|
.Xr socketpair 2 ,
|
.Xr write 2 ,
|
.Xr write 2 ,
|
.Xr getprotoent 3 ,
|
.Xr getprotoent 3 ,
|
.Xr netintro 4
|
.Xr netintro 4
|
.Rs
|
.Rs
|
.%T "An Introductory 4.3 BSD Interprocess Communication Tutorial"
|
.%T "An Introductory 4.3 BSD Interprocess Communication Tutorial"
|
.%O "reprinted in UNIX Programmer's Supplementary Documents Volume 1"
|
.%O "reprinted in UNIX Programmer's Supplementary Documents Volume 1"
|
.Re
|
.Re
|
.Rs
|
.Rs
|
.%T "BSD Interprocess Communication Tutorial"
|
.%T "BSD Interprocess Communication Tutorial"
|
.%O "reprinted in UNIX Programmer's Supplementary Documents Volume 1"
|
.%O "reprinted in UNIX Programmer's Supplementary Documents Volume 1"
|
.Re
|
.Re
|
.Sh HISTORY
|
.Sh HISTORY
|
The
|
The
|
.Fn socket
|
.Fn socket
|
function call appeared in
|
function call appeared in
|
.Bx 4.2 .
|
.Bx 4.2 .
|
|
|
