a4b155d7a2
Stop calling system calls "function calls". Use "The .Fn system call" a-la "The .Nm utility". When referring to a non-BSD implementation in the HISTORY section, call syscall a function, to be safe.
404 lines
12 KiB
Groff
404 lines
12 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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.\" @(#)getsockopt.2 8.4 (Berkeley) 5/2/95
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.\" $FreeBSD$
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.\"
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.Dd May 2, 1995
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.Dt GETSOCKOPT 2
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.Os
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.Sh NAME
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.Nm getsockopt ,
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.Nm setsockopt
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.Nd get and set options on sockets
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In sys/types.h
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.In sys/socket.h
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.Ft int
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.Fn getsockopt "int s" "int level" "int optname" "void *optval" "socklen_t *optlen"
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.Ft int
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.Fn setsockopt "int s" "int level" "int optname" "const void *optval" "socklen_t optlen"
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.Sh DESCRIPTION
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The
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.Fn getsockopt
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and
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.Fn setsockopt
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system calls
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manipulate the
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.Em options
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associated with a socket. Options may exist at multiple
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protocol levels; they are always present at the uppermost
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.Dq socket
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level.
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.Pp
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When manipulating socket options the level at which the
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option resides and the name of the option must be specified.
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To manipulate options at the socket level,
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.Fa level
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is specified as
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.Dv SOL_SOCKET .
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To manipulate options at any
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other level the protocol number of the appropriate protocol
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controlling the option is supplied. For example,
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to indicate that an option is to be interpreted by the
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.Tn TCP
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protocol,
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.Fa level
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should be set to the protocol number of
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.Tn TCP ;
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see
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.Xr getprotoent 3 .
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.Pp
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The parameters
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.Fa optval
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and
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.Fa optlen
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are used to access option values for
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.Fn setsockopt .
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For
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.Fn getsockopt
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they identify a buffer in which the value for the
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requested option(s) are to be returned. For
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.Fn getsockopt ,
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.Fa optlen
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is a value-result parameter, initially containing the
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size of the buffer pointed to by
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.Fa optval ,
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and modified on return to indicate the actual size of
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the value returned. If no option value is
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to be supplied or returned,
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.Fa optval
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may be NULL.
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.Pp
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.Fa Optname
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and any specified options are passed uninterpreted to the appropriate
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protocol module for interpretation.
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The include file
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.Ao Pa sys/socket.h Ac
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contains definitions for
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socket level options, described below.
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Options at other protocol levels vary in format and
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name; consult the appropriate entries in
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section
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4 of the manual.
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.Pp
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Most socket-level options utilize an
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.Fa int
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parameter for
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.Fa optval .
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For
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.Fn setsockopt ,
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the parameter should be non-zero to enable a boolean option,
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or zero if the option is to be disabled.
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.Dv SO_LINGER
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uses a
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.Fa struct linger
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parameter, defined in
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.Ao Pa sys/socket.h Ac ,
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which specifies the desired state of the option and the
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linger interval (see below).
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.Dv SO_SNDTIMEO
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and
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.Dv SO_RCVTIMEO
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use a
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.Fa struct timeval
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parameter, defined in
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.Ao Pa sys/time.h Ac .
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.Pp
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The following options are recognized at the socket level.
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Except as noted, each may be examined with
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.Fn getsockopt
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and set with
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.Fn setsockopt .
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.Bl -column SO_ACCEPTFILTER -offset indent
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.It Dv SO_DEBUG Ta "enables recording of debugging information"
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.It Dv SO_REUSEADDR Ta "enables local address reuse"
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.It Dv SO_REUSEPORT Ta "enables duplicate address and port bindings"
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.It Dv SO_KEEPALIVE Ta "enables keep connections alive"
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.It Dv SO_DONTROUTE Ta "enables routing bypass for outgoing messages"
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.It Dv SO_LINGER Ta "linger on close if data present"
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.It Dv SO_BROADCAST Ta "enables permission to transmit broadcast messages"
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.It Dv SO_OOBINLINE Ta "enables reception of out-of-band data in band"
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.It Dv SO_SNDBUF Ta "set buffer size for output"
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.It Dv SO_RCVBUF Ta "set buffer size for input"
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.It Dv SO_SNDLOWAT Ta "set minimum count for output"
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.It Dv SO_RCVLOWAT Ta "set minimum count for input"
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.It Dv SO_SNDTIMEO Ta "set timeout value for output"
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.It Dv SO_RCVTIMEO Ta "set timeout value for input"
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.It Dv SO_ACCEPTFILTER Ta "set accept filter on listening socket"
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.It Dv SO_TYPE Ta "get the type of the socket (get only)"
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.It Dv SO_ERROR Ta "get and clear error on the socket (get only)"
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.El
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.Pp
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.Dv SO_DEBUG
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enables debugging in the underlying protocol modules.
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.Dv SO_REUSEADDR
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indicates that the rules used in validating addresses supplied
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in a
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.Xr bind 2
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system call should allow reuse of local addresses.
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.Dv SO_REUSEPORT
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allows completely duplicate bindings by multiple processes
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if they all set
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.Dv SO_REUSEPORT
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before binding the port.
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This option permits multiple instances of a program to each
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receive UDP/IP multicast or broadcast datagrams destined for the bound port.
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.Dv SO_KEEPALIVE
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enables the
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periodic transmission of messages on a connected socket. Should the
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connected party fail to respond to these messages, the connection is
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considered broken and processes using the socket are notified via a
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.Dv SIGPIPE
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signal when attempting to send data.
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.Dv SO_DONTROUTE
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indicates that outgoing messages should
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bypass the standard routing facilities. Instead, messages are directed
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to the appropriate network interface according to the network portion
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of the destination address.
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.Pp
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.Dv SO_LINGER
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controls the action taken when unsent messages
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are queued on socket and a
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.Xr close 2
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is performed.
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If the socket promises reliable delivery of data and
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.Dv SO_LINGER
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is set,
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the system will block the process on the
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.Xr close 2
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attempt until it is able to transmit the data or until it decides it
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is unable to deliver the information (a timeout period, termed the
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linger interval, is specified in seconds in the
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.Fn setsockopt
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system call when
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.Dv SO_LINGER
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is requested).
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If
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.Dv SO_LINGER
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is disabled and a
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.Xr close 2
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is issued, the system will process the close in a manner that allows
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the process to continue as quickly as possible.
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.Pp
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The option
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.Dv SO_BROADCAST
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requests permission to send broadcast datagrams
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on the socket.
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Broadcast was a privileged operation in earlier versions of the system.
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With protocols that support out-of-band data, the
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.Dv SO_OOBINLINE
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option
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requests that out-of-band data be placed in the normal data input queue
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as received; it will then be accessible with
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.Xr recv 2
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or
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.Xr read 2
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calls without the
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.Dv MSG_OOB
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flag.
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Some protocols always behave as if this option is set.
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.Dv SO_SNDBUF
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and
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.Dv SO_RCVBUF
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are options to adjust the normal
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buffer sizes allocated for output and input buffers, respectively.
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The buffer size may be increased for high-volume connections,
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or may be decreased to limit the possible backlog of incoming data.
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The system places an absolute maximum on these values, which is accessible
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through the
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.Xr sysctl 3
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MIB variable
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.Dq Li kern.ipc.maxsockbuf .
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.Pp
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.Dv SO_SNDLOWAT
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is an option to set the minimum count for output operations.
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Most output operations process all of the data supplied
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by the call, delivering data to the protocol for transmission
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and blocking as necessary for flow control.
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Nonblocking output operations will process as much data as permitted
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subject to flow control without blocking, but will process no data
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if flow control does not allow the smaller of the low water mark value
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or the entire request to be processed.
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A
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.Xr select 2
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operation testing the ability to write to a socket will return true
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only if the low water mark amount could be processed.
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The default value for
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.Dv SO_SNDLOWAT
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is set to a convenient size for network efficiency, often 1024.
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.Dv SO_RCVLOWAT
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is an option to set the minimum count for input operations.
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In general, receive calls will block until any (non-zero) amount of data
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is received, then return with the smaller of the amount available or the amount
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requested.
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The default value for
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.Dv SO_RCVLOWAT
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is 1.
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If
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.Dv SO_RCVLOWAT
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is set to a larger value, blocking receive calls normally
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wait until they have received the smaller of the low water mark value
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or the requested amount.
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Receive calls may still return less than the low water mark if an error
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occurs, a signal is caught, or the type of data next in the receive queue
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is different from that which was returned.
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.Pp
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.Dv SO_SNDTIMEO
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is an option to set a timeout value for output operations.
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It accepts a
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.Fa struct timeval
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parameter with the number of seconds and microseconds
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used to limit waits for output operations to complete.
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If a send operation has blocked for this much time,
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it returns with a partial count
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or with the error
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.Er EWOULDBLOCK
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if no data were sent.
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In the current implementation, this timer is restarted each time additional
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data are delivered to the protocol,
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implying that the limit applies to output portions ranging in size
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from the low water mark to the high water mark for output.
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.Dv SO_RCVTIMEO
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is an option to set a timeout value for input operations.
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It accepts a
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.Fa struct timeval
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parameter with the number of seconds and microseconds
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used to limit waits for input operations to complete.
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In the current implementation, this timer is restarted each time additional
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data are received by the protocol,
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and thus the limit is in effect an inactivity timer.
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If a receive operation has been blocked for this much time without
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receiving additional data, it returns with a short count
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or with the error
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.Er EWOULDBLOCK
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if no data were received.
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.Pp
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.Dv SO_ACCEPTFILTER
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places an
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.Xr accept_filter 9
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on the socket,
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which will filter incoming connections
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on a listening stream socket before being presented for
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.Xr accept 2 .
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Once more,
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.Xr listen 2
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must be called on the socket before
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trying to install the filter on it,
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or else the
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.Fn setsockopt
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system call will fail.
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.Bd -literal
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struct accept_filter_arg {
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char af_name[16];
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char af_arg[256-16];
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};
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.Ed
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.Pp
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.Fa optval
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should point to a
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.Fa struct accept_filter_arg
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that will select and configure the
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.Xr accept_filter 9 .
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.Fa af_name
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should be filled with the name of the accept filter
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that the application wishes to place on the listening socket.
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.Fa af_arg
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is an optional parameter that can be passed to the accept
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filter specified by
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.Fa af_name
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to provide additional configuration options at attach time.
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Passing in an
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.Fa optval
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of NULL will remove the filter.
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.Pp
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Finally,
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.Dv SO_TYPE
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and
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.Dv SO_ERROR
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are options used only with
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.Fn getsockopt .
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.Dv SO_TYPE
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returns the type of the socket, such as
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.Dv SOCK_STREAM ;
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it is useful for servers that inherit sockets on startup.
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.Dv SO_ERROR
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returns any pending error on the socket and clears
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the error status.
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It may be used to check for asynchronous errors on connected
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datagram sockets or for other asynchronous errors.
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.Sh RETURN VALUES
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.Rv -std
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.Sh ERRORS
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The call succeeds unless:
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.Bl -tag -width Er
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.It Bq Er EBADF
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The argument
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.Fa s
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is not a valid descriptor.
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.It Bq Er ENOTSOCK
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The argument
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.Fa s
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is a file, not a socket.
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.It Bq Er ENOPROTOOPT
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The option is unknown at the level indicated.
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.It Bq Er EFAULT
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The address pointed to by
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.Fa optval
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is not in a valid part of the process address space.
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For
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.Fn getsockopt ,
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this error may also be returned if
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.Fa optlen
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is not in a valid part of the process address space.
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.It Bq Er EINVAL
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Installing an
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.Xr accept_filter 9
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on a non-listening socket was attempted.
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.El
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.Sh SEE ALSO
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.Xr ioctl 2 ,
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.Xr socket 2 ,
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.Xr getprotoent 3 ,
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.Xr sysctl 3 ,
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.Xr protocols 5 ,
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.Xr sysctl 8 ,
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.Xr accept_filter 9
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.Sh BUGS
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Several of the socket options should be handled at lower levels of the system.
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.Sh HISTORY
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The
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.Fn getsockopt
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system call appeared in
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.Bx 4.2 .
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