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Name
connect — initiate a connection on a socket
Synopsis
int
connect( |
int |
sockfd, |
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const struct sockaddr
* |
serv_addr, |
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socklen_t |
addrlen); |
DESCRIPTION
The connect() system call
connects the socket referred to by the file descriptor
sockfd to the address
specified by serv_addr. The addrlen argument specifies the
size of serv_addr.
The format of the address in serv_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 serv_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 serv_addr.
Generally, connection-based protocol sockets may
successfully connect() only
once; connectionless protocol sockets may use connect() multiple times to change their
association. Connectionless sockets may dissolve the
association by connecting to an address with the sa_family member of
sockaddr set to
AF_UNSPEC.
RETURN VALUE
If the connection or binding succeeds, zero is returned.
On error, −1 is returned, and errno is set appropriately.
ERRORS
The following are general socket errors only. There may be
other domain-specific error codes.
- EACCES
-
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).)
- EACCES,
EPERM
-
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.
- EADDRINUSE
-
Local address is already in use.
- EAFNOSUPPORT
-
The passed address didn't have the correct address
family in its sa_family field.
- EAGAIN
-
No more free local ports or insufficient entries in
the routing cache. For PF_INET see the net.ipv4.ip_local_port_range
sysctl in ip(7) on how to
increase the number of local ports.
- EALREADY
-
The socket is non-blocking and a previous connection
attempt has not yet been completed.
- EBADF
-
The file descriptor is not a valid index in the
descriptor table.
- ECONNREFUSED
-
No one listening on the remote address.
- EFAULT
-
The socket structure address is outside the user's
address space.
- EINPROGRESS
-
The socket is non-blocking and the connection cannot
be completed immediately. 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).
- EINTR
-
The system call was interrupted by a signal that was
caught.
- EISCONN
-
The socket is already connected.
- ENETUNREACH
-
Network is unreachable.
- ENOTSOCK
-
The file descriptor is not associated with a
socket.
- ETIMEDOUT
-
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.
CONFORMING TO
SVr4, 4.4BSD, (the connect()
function first appeared in 4.2BSD), POSIX.1-2001.
NOTES
The third argument of connect() is in reality an int (and this is what 4.x BSD
and libc4 and libc5 have). Some POSIX confusion resulted in
the present socklen_t, also used by
glibc. See also accept(2).
BUGS
Unconnecting a socket by calling connect() with a AF_UNSPEC address is not yet
implemented.
EXAMPLE
An example of the use of connect() is shown in getaddrinfo(3).
SEE ALSO
accept(2), bind(2), getsockname(2), listen(2), socket(2), path_resolution(7)
Copyright 1993 Rickard E. Faith (faith@cs.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.
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.
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.
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.
Modified 1997-01-31 by Eric S. Raymond <esr@thyrsus.com>
Modified 1998, 1999 by Andi Kleen
Modified 2004-06-23 by Michael Kerrisk <mtk-manpages@gmx.net>
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