connect — initiate a connection on a socket
#include <sys/socket.h>
int
connect( |
int sockfd, |
| const struct sockaddr *addr, | |
socklen_t addrlen); |
The connect() system call
connects the socket referred to by the file descriptor
sockfd to the address
specified by addr.
The addrlen argument
specifies the size of addr. The format of the address
in addr is determined
by the address space of the socket sockfd; see socket(2) for further
details.
If the socket sockfd is of type SOCK_DGRAM, then addr is the address to which
datagrams are sent by default, and the only address from
which datagrams are received. If the socket is of type
SOCK_STREAM or SOCK_SEQPACKET, this call attempts to make
a connection to the socket that is bound to the address
specified by addr.
Some protocol sockets (e.g., UNIX domain stream sockets)
may successfully connect() only
once.
Some protocol sockets (e.g., datagram sockets in the UNIX
and Internet domains) may use connect() multiple times to change their
association.
Some protocol sockets (e.g., TCP sockets as well as
datagram sockets in the UNIX and Internet domains) may
dissolve the association by connecting to an address with the
sa_family member of
sockaddr set to AF_UNSPEC; thereafter, the socket can be
connected to another address. (AF_UNSPEC is supported on Linux since
kernel 2.2.)
If the connection or binding succeeds, zero is returned.
On error, −1 is returned, and errno is set to indicate the error.
The following are general socket errors only. There may be other domain-specific error codes.
For UNIX domain sockets, which are identified by pathname: Write permission is denied on the socket file, or search permission is denied for one of the directories in the path prefix. (See also path_resolution(7).)
The user tried to connect to a broadcast address without having the socket broadcast flag enabled or the connection request failed because of a local firewall rule.
EACCES can also be returned if an SELinux policy denied a connection (for example, if there is a policy saying that an HTTP proxy can only connect to ports associated with HTTP servers, and the proxy tries to connect to a different port). dd
Local address is already in use.
(Internet domain sockets) The socket referred to by
sockfd had not
previously been bound to an address and, upon
attempting to bind it to an ephemeral port, it was
determined that all port numbers in the ephemeral port
range are currently in use. See the discussion of
/proc/sys/net/ipv4/ip_local_port_range
in ip(7).
The passed address didn't have the correct address
family in its sa_family field.
For nonblocking UNIX domain sockets, the socket is nonblocking, and the connection cannot be completed immediately. For other socket families, there are insufficient entries in the routing cache.
The socket is nonblocking and a previous connection attempt has not yet been completed.
sockfd is
not a valid open file descriptor.
A connect() on a
stream socket found no one listening on the remote
address.
The socket structure address is outside the user's address space.
The socket is nonblocking and the connection cannot
be completed immediately. (UNIX domain sockets failed
with EAGAIN instead.) It
is possible to select(2) or
poll(2) for
completion by selecting the socket for writing. After
select(2) indicates
writability, use getsockopt(2) to read
the SO_ERROR option at
level SOL_SOCKET to
determine whether connect() completed successfully
(SO_ERROR is zero) or
unsuccessfully (SO_ERROR
is one of the usual error codes listed here, explaining
the reason for the failure).
The system call was interrupted by a signal that was caught; see signal(7).
The socket is already connected.
Network is unreachable.
The file descriptor sockfd does not refer to
a socket.
The socket type does not support the requested communications protocol. This error can occur, for example, on an attempt to connect a UNIX domain datagram socket to a stream socket.
Timeout while attempting connection. The server may be too busy to accept new connections. Note that for IP sockets the timeout may be very long when syncookies are enabled on the server.
For background on the socklen_t type, see accept(2).
If connect() fails, consider
the state of the socket as unspecified. Portable applications
should close the socket and create a new one for
reconnecting.
This page is part of release 5.11 of the Linux man-pages project. A
description of the project, information about reporting bugs,
and the latest version of this page, can be found at
https://www.kernel.org/doc/man−pages/.
|
Copyright 1993 Rickard E. Faith (faithcs.unc.edu) Portions extracted from /usr/include/sys/socket.h, which does not have any authorship information in it. It is probably available under the GPL. %%%LICENSE_START(VERBATIM) Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Since the Linux kernel and libraries are constantly changing, this manual page may be incorrect or out-of-date. The author(s) assume no responsibility for errors or omissions, or for damages resulting from the use of the information contained herein. The author(s) may not have taken the same level of care in the production of this manual, which is licensed free of charge, as they might when working professionally. Formatted or processed versions of this manual, if unaccompanied by the source, must acknowledge the copyright and authors of this work. %%%LICENSE_END Other portions are from the 6.9 (Berkeley) 3/10/91 man page: Copyright (c) 1983 The Regents of the University of California. All rights reserved. %%%LICENSE_START(BSD_4_CLAUSE_UCB) Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: 1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. 2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution. 3. All advertising materials mentioning features or use of this software must display the following acknowledgement: This product includes software developed by the University of California, Berkeley and its contributors. 4. Neither the name of the University nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission. THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. %%%LICENSE_END Modified 1997-01-31 by Eric S. Raymond <esrthyrsus.com> Modified 1998, 1999 by Andi Kleen Modified 2004-06-23 by Michael Kerrisk <mtk.manpagesgmail.com> |