258 lines
7.1 KiB
Groff
258 lines
7.1 KiB
Groff
.\" $OpenBSD: connect.2,v 1.34 2019/06/20 14:19:25 deraadt Exp $
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.\" $NetBSD: connect.2,v 1.8 1995/10/12 15:40:48 jtc Exp $
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.\"
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.\" Copyright (c) 1983, 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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.\" @(#)connect.2 8.1 (Berkeley) 6/4/93
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.\"
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.Dd $Mdocdate: June 20 2019 $
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.Dt CONNECT 2
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.Os
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.Sh NAME
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.Nm connect
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.Nd initiate a connection on a socket
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.Sh SYNOPSIS
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.In sys/socket.h
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.Ft int
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.Fn connect "int s" "const struct sockaddr *name" "socklen_t namelen"
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.Sh DESCRIPTION
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The parameter
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.Fa s
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is a socket.
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If it is of type
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.Dv SOCK_DGRAM ,
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this call specifies the peer with which the socket is to be associated;
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this address is that to which datagrams are to be sent,
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and the only address from which datagrams are to be received.
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If the socket is of type
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.Dv SOCK_STREAM ,
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this call attempts to make a connection to
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another socket.
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The other socket is specified by
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.Fa name ,
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which is an address in the communications space of the socket.
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.Fa namelen
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indicates the amount of space pointed to by
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.Fa name ,
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in bytes; the
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.Fa sa_len
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member of
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.Fa name
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is ignored.
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Each communications space interprets the
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.Fa name
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parameter in its own way.
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Generally, stream sockets may use
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.Fn connect
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only once; datagram sockets may use
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.Fn connect
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multiple times to change their association.
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Datagram sockets may dissolve the association
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by connecting to an invalid address, such as a null address.
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.Pp
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If the socket is in non-blocking mode and the connection cannot be
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completed immediately, or if it is interrupted by a signal,
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.Fn connect
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will return an error and the connection attempt will proceed
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asynchronously.
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Subsequent calls to
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.Fn connect
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will fail with errno set to
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.Er EALREADY .
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It is possible to use
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.Xr select 2
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or
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.Xr poll 2
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to determine when the connect operation has completed by checking the
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socket for writability.
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The success or failure of the connection attempt may be determined by using
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.Xr getsockopt 2
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to check the socket error status with the
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.Dv SO_ERROR
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option at the
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.Dv SOL_SOCKET
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level.
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If the connection was successful, the error value will be zero.
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Otherwise, it will be one of the error values listed below.
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.Sh RETURN VALUES
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If the connection or binding succeeds, 0 is returned.
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Otherwise a \-1 is returned, and a more specific error
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code is stored in
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.Va errno .
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.Sh EXAMPLES
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The following code connects to the host described by
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.Fa name
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and handles the case where
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.Fn connect
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is interrupted by a signal.
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.Bd -literal -offset indent
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#include <sys/socket.h>
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#include <poll.h>
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#include <errno.h>
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#include <err.h>
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int
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connect_wait(int s)
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{
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struct pollfd pfd[1];
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int error = 0;
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socklen_t len = sizeof(error);
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pfd[0].fd = s;
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pfd[0].events = POLLOUT;
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if (poll(pfd, 1, -1) == -1)
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return -1;
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if (getsockopt(s, SOL_SOCKET, SO_ERROR, &error, &len) == -1)
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return -1;
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if (error != 0) {
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errno = error;
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return -1;
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}
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return 0;
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}
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\&...
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int retcode;
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\&...
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for (retcode = connect(s, name, namelen);
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retcode == -1 && errno == EINTR;
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retcode = connect_wait(s))
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continue;
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if (retcode == -1)
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err(1, "connect");
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.Ed
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.Sh ERRORS
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The
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.Fn connect
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call fails if:
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.Bl -tag -width Er
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.It Bq Er EBADF
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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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.Fa s
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is not a socket.
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.It Bq Er EADDRNOTAVAIL
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No suitable address is available on the local machine.
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.It Bq Er EAFNOSUPPORT
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Addresses in the specified address family cannot be used with this socket.
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.It Bq Er EISCONN
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The socket is already connected.
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.It Bq Er ETIMEDOUT
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Connection establishment timed out without establishing a connection.
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.It Bq Er EINVAL
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A TCP connection with a local broadcast, the all-ones or a
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multicast address as the peer was attempted.
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.It Bq Er ECONNREFUSED
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The attempt to connect was forcefully rejected.
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.It Bq Er EHOSTUNREACH
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The destination address specified an unreachable host.
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.It Bq Er EINTR
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The connection attempt was interrupted by a signal.
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The attempt will continue asynchronously as if the socket was non-blocking.
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.It Bq Er ENETUNREACH
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The network isn't reachable from this host.
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.It Bq Er EADDRINUSE
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The address is already in use.
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.It Bq Er EFAULT
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The
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.Fa name
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parameter specifies an area outside
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the process address space.
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.It Bq Er EINPROGRESS
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The socket is non-blocking and the connection cannot
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be completed immediately.
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.It Bq Er EALREADY
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Either the socket is non-blocking or a previous call to
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.Fn connect
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was interrupted by a signal, and the connection attempt has not yet
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been completed.
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.It Bq Er EPERM
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A TCP connection on a socket with socket option TCP_MD5SIG was
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attempted without configuring the security parameters correctly.
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.El
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.Pp
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The following errors are specific to connecting names in the
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.Ux Ns -domain .
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These errors may not apply in future versions of the
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.Ux
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IPC domain.
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.Bl -tag -width Er
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.It Bq Er ENOTDIR
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A component of the path prefix is not a directory.
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.It Bq Er ENAMETOOLONG
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A component of a pathname exceeded
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.Dv NAME_MAX
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characters, or an entire pathname (including the terminating NUL)
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exceeded
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.Dv PATH_MAX
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bytes.
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.It Bq Er ENOENT
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The named socket does not exist.
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.It Bq Er EACCES
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Search permission is denied for a component of the path prefix.
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.It Bq Er EACCES
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Write access to the named socket is denied.
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.It Bq Er ELOOP
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Too many symbolic links were encountered in translating the pathname.
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.It Bq Er EPROTOTYPE
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The file described by
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.Fa name
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is of a different type than
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.Fa s .
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E.g.,
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.Fa s
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may be of type
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.Dv SOCK_STREAM
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whereas
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.Fa name
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may refer to a socket of type
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.Dv SOCK_DGRAM .
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.El
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.Sh SEE ALSO
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.Xr accept 2 ,
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.Xr getsockname 2 ,
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.Xr getsockopt 2 ,
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.Xr poll 2 ,
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.Xr select 2 ,
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.Xr socket 2
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.Sh STANDARDS
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The
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.Fn connect
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function conforms to
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.St -p1003.1-2008 .
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.Sh HISTORY
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The
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.Fn connect
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system call first appeared in
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.Bx 4.1c .
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