fbbd9655e5
Renumber cluase 4 to 3, per what everybody else did when BSD granted them permission to remove clause 3. My insistance on keeping the same numbering for legal reasons is too pedantic, so give up on that point. Submitted by: Jan Schaumann <jschauma@stevens.edu> Pull Request: https://github.com/freebsd/freebsd/pull/96
240 lines
6.1 KiB
Groff
240 lines
6.1 KiB
Groff
.\" Copyright (c) 1983, 1990, 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. 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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.\" @(#)accept.2 8.2 (Berkeley) 12/11/93
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.\" $FreeBSD$
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.\"
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.Dd October 9, 2014
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.Dt ACCEPT 2
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.Os
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.Sh NAME
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.Nm accept ,
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.Nm accept4
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.Nd accept a connection on a socket
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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 accept "int s" "struct sockaddr * restrict addr" "socklen_t * restrict addrlen"
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.Ft int
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.Fn accept4 "int s" "struct sockaddr * restrict addr" "socklen_t * restrict addrlen" "int flags"
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.Sh DESCRIPTION
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The argument
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.Fa s
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is a socket that has been created with
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.Xr socket 2 ,
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bound to an address with
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.Xr bind 2 ,
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and is listening for connections after a
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.Xr listen 2 .
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The
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.Fn accept
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system call extracts the first connection request on the
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queue of pending connections, creates a new socket,
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and allocates a new file descriptor for the socket which
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inherits the state of the
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.Dv O_NONBLOCK
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and
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.Dv O_ASYNC
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properties and the destination of
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.Dv SIGIO
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and
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.Dv SIGURG
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signals from the original socket
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.Fa s .
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.Pp
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The
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.Fn accept4
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system call is similar,
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but the
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.Dv O_NONBLOCK
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property of the new socket is instead determined by the
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.Dv SOCK_NONBLOCK
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flag in the
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.Fa flags
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argument,
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the
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.Dv O_ASYNC
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property is cleared,
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the signal destination is cleared
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and the close-on-exec flag on the new file descriptor can be set via the
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.Dv SOCK_CLOEXEC
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flag in the
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.Fa flags
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argument.
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.Pp
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If no pending connections are
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present on the queue, and the original socket
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is not marked as non-blocking,
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.Fn accept
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blocks the caller until a connection is present.
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If the original socket
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is marked non-blocking and no pending
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connections are present on the queue,
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.Fn accept
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returns an error as described below.
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The accepted socket
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may not be used
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to accept more connections.
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The original socket
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.Fa s
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remains open.
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.Pp
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The argument
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.Fa addr
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is a result argument that is filled-in with
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the address of the connecting entity,
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as known to the communications layer.
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The exact format of the
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.Fa addr
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argument is determined by the domain in which the communication
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is occurring.
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A null pointer may be specified for
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.Fa addr
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if the address information is not desired;
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in this case,
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.Fa addrlen
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is not used and should also be null.
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Otherwise, the
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.Fa addrlen
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argument
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is a value-result argument; it should initially contain the
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amount of space pointed to by
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.Fa addr ;
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on return it will contain the actual length (in bytes) of the
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address returned.
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This call
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is used with connection-based socket types, currently with
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.Dv SOCK_STREAM .
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.Pp
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It is possible to
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.Xr select 2
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a socket for the purposes of doing an
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.Fn accept
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by selecting it for read.
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.Pp
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For certain protocols which require an explicit confirmation,
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such as
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.Tn ISO
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or
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.Tn DATAKIT ,
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.Fn accept
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can be thought of
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as merely dequeueing the next connection
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request and not implying confirmation.
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Confirmation can be implied by a normal read or write on the new
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file descriptor, and rejection can be implied by closing the
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new socket.
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.Pp
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For some applications, performance may be enhanced by using an
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.Xr accept_filter 9
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to pre-process incoming connections.
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.Pp
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When using
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.Fn accept ,
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portable programs should not rely on the
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.Dv O_NONBLOCK
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and
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.Dv O_ASYNC
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properties and the signal destination being inherited,
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but should set them explicitly using
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.Xr fcntl 2 ;
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.Fn accept4
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sets these properties consistently,
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but may not be fully portable across
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.Ux
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platforms.
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.Sh RETURN VALUES
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These calls return \-1 on error.
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If they succeed, they return a non-negative
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integer that is a descriptor for the accepted socket.
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.Sh ERRORS
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The
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.Fn accept
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and
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.Fn accept4
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system calls will fail if:
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.Bl -tag -width Er
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.It Bq Er EBADF
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The descriptor is invalid.
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.It Bq Er EINTR
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The
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.Fn accept
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operation was interrupted.
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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 ENOTSOCK
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The descriptor references a file, not a socket.
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.It Bq Er EINVAL
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.Xr listen 2
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has not been called on the socket descriptor.
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.It Bq Er EFAULT
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The
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.Fa addr
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argument is not in a writable part of the
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user address space.
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.It Bo Er EWOULDBLOCK Bc or Bq Er EAGAIN
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The socket is marked non-blocking and no connections
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are present to be accepted.
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.It Bq Er ECONNABORTED
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A connection arrived, but it was closed while waiting
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on the listen queue.
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.El
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.Pp
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The
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.Fn accept4
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system call will also fail if:
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.Bl -tag -width Er
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.It Bq Er EINVAL
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The
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.Fa flags
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argument is invalid.
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.El
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.Sh SEE ALSO
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.Xr bind 2 ,
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.Xr connect 2 ,
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.Xr getpeername 2 ,
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.Xr getsockname 2 ,
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.Xr listen 2 ,
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.Xr select 2 ,
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.Xr socket 2 ,
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.Xr accept_filter 9
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.Sh HISTORY
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The
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.Fn accept
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system call appeared in
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.Bx 4.2 .
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.Pp
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The
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.Fn accept4
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system call appeared in
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.Fx 10.0 .
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