'\" et

.TH CONNECT "3P" 2013 "IEEE/The Open Group" "POSIX Programmer's Manual"

.SH PROLOG

This manual page is part of the POSIX Programmer's Manual.

The Linux implementation of this interface may differ (consult

the corresponding Linux manual page for details of Linux behavior),

or the interface may not be implemented on Linux.

.SH NAME

connect

\(em connect a socket

.SH SYNOPSIS

.LP

.nf

#include <sys/socket.h>

.P

int connect(int \fIsocket\fP, const struct sockaddr *\fIaddress\fP,

    socklen_t \fIaddress_len\fP);

.fi

.SH DESCRIPTION

The

\fIconnect\fR()

function shall attempt to make a connection on a connection-mode

socket or to set or reset the peer address of a connectionless-mode

socket. The function takes the following arguments:

.IP "\fIsocket\fR" 12

Specifies the file descriptor associated with the socket.

.IP "\fIaddress\fR" 12

Points to a

.BR sockaddr

structure containing the peer address. The length and format of the

address depend on the address family of the socket.

.IP "\fIaddress_len\fR" 12

Specifies the length of the

.BR sockaddr

structure pointed to by the

.IR address

argument.

.P

If the socket has not already been bound to a local address,

\fIconnect\fR()

shall bind it to an address which, unless the socket's address family

is AF_UNIX, is an unused local address.

.P

If the initiating socket is not connection-mode, then

\fIconnect\fR()

shall set the socket's peer address, and no connection is made. For

SOCK_DGRAM sockets, the peer address identifies where all datagrams are

sent on subsequent

\fIsend\fR()

functions, and limits the remote sender for subsequent

\fIrecv\fR()

functions. If the

.IR sa_family

member of

.IR address

is AF_UNSPEC, the socket's peer address shall be reset. Note that despite

no connection being made, the term ``connected'' is used to describe a

connectionless-mode socket for which a peer address has been set.

.P

If the initiating socket is connection-mode, then

\fIconnect\fR()

shall attempt to establish a connection to the address specified by the

.IR address

argument. If the connection cannot be established immediately and

O_NONBLOCK is not set for the file descriptor for the socket,

\fIconnect\fR()

shall block for up to an unspecified timeout interval until the

connection is established. If the timeout interval expires before the

connection is established,

\fIconnect\fR()

shall fail and the connection attempt shall be aborted. If

\fIconnect\fR()

is interrupted by a signal that is caught while blocked waiting to

establish a connection,

\fIconnect\fR()

shall fail and set

.IR errno

to

.BR [EINTR] ,

but the connection request shall not be aborted, and the connection

shall be established asynchronously.

.P

If the connection cannot be established immediately and O_NONBLOCK is

set for the file descriptor for the socket,

\fIconnect\fR()

shall fail and set

.IR errno

to

.BR [EINPROGRESS] ,

but the connection request shall not be aborted, and the connection

shall be established asynchronously. Subsequent calls to

\fIconnect\fR()

for the same socket, before the connection is established, shall fail

and set

.IR errno

to

.BR [EALREADY] .

.P

When the connection has been established asynchronously,

\fIpselect\fR(),

\fIselect\fR(),

and

\fIpoll\fR()

shall indicate that the file descriptor for the socket is ready for

writing.

.P

The socket in use may require the process to have appropriate

privileges to use the

\fIconnect\fR()

function.

.SH "RETURN VALUE"

Upon successful completion,

\fIconnect\fR()

shall return 0; otherwise, \(mi1 shall be returned and

.IR errno

set to indicate the error.

.SH ERRORS

The

\fIconnect\fR()

function shall fail if:

.TP

.BR EADDRNOTAVAIL

.br

The specified address is not available from the local machine.

.TP

.BR EAFNOSUPPORT

.br

The specified address is not a valid address for the address family of

the specified socket.

.TP

.BR EALREADY

A connection request is already in progress for the specified socket.

.TP

.BR EBADF

The

.IR socket

argument is not a valid file descriptor.

.TP

.BR ECONNREFUSED

.br

The target address was not listening for connections or refused the

connection request.

.TP

.BR EINPROGRESS

O_NONBLOCK is set for the file descriptor for the socket and the

connection cannot be immediately established; the connection shall be

established asynchronously.

.TP

.BR EINTR

The attempt to establish a connection was interrupted by delivery of a

signal that was caught; the connection shall be established

asynchronously.

.TP

.BR EISCONN

The specified socket is connection-mode and is already connected.

.TP

.BR ENETUNREACH

.br

No route to the network is present.

.TP

.BR ENOTSOCK

The

.IR socket

argument does not refer to a socket.

.TP

.BR EPROTOTYPE

The specified address has a different type than the socket bound to the

specified peer address.

.TP

.BR ETIMEDOUT

The attempt to connect timed out before a connection was made.

.P

If the address family of the socket is AF_UNIX, then

\fIconnect\fR()

shall fail if:

.TP

.BR EIO

An I/O error occurred while reading from or writing to the file system.

.TP

.BR ELOOP

A loop exists in symbolic links encountered during resolution of the

pathname in

.IR address .

.TP

.BR ENAMETOOLONG

.br

The length of a component of a pathname is longer than

{NAME_MAX}.

.TP

.BR ENOENT

A component of the pathname does not name an existing file or the

pathname is an empty string.

.TP

.BR ENOTDIR

A component of the path prefix of the pathname in

.IR address

names an existing file that is neither a directory nor a symbolic link

to a directory, or the pathname in

.IR address

contains at least one non-\c

<slash>

character and ends with one or more trailing

<slash>

characters and the last pathname component names an existing file that

is neither a directory nor a symbolic link to a directory.

.P

The

\fIconnect\fR()

function may fail if:

.TP

.BR EACCES

Search permission is denied for a component of the path prefix; or

write access to the named socket is denied.

.TP

.BR EADDRINUSE

Attempt to establish a connection that uses addresses that are already

in use.

.TP

.BR ECONNRESET

Remote host reset the connection request.

.TP

.BR EHOSTUNREACH

.br

The destination host cannot be reached (probably because the host is

down or a remote router cannot reach it).

.TP

.BR EINVAL

The

.IR address_len

argument is not a valid length for the address family; or invalid

address family in the

.BR sockaddr

structure.

.TP

.BR ELOOP

More than

{SYMLOOP_MAX}

symbolic links were encountered during resolution of the pathname in

.IR address .

.TP

.BR ENAMETOOLONG

.br

The length of a pathname exceeds

{PATH_MAX},

or pathname resolution of a symbolic link produced an intermediate

result with a length that exceeds

{PATH_MAX}.

.TP

.BR ENETDOWN

The local network interface used to reach the destination is down.

.TP

.BR ENOBUFS

No buffer space is available.

.TP

.BR EOPNOTSUPP

The socket is listening and cannot be connected.

.LP

.IR "The following sections are informative."

.SH EXAMPLES

None.

.SH "APPLICATION USAGE"

If

\fIconnect\fR()

fails, the state of the socket is unspecified. Conforming applications

should close the file descriptor and create a new socket before

attempting to reconnect.

.SH "RATIONALE"

None.

.SH "FUTURE DIRECTIONS"

None.

.SH "SEE ALSO"

.IR "\fIaccept\fR\^(\|)",

.IR "\fIbind\fR\^(\|)",

.IR "\fIclose\fR\^(\|)",

.IR "\fIgetsockname\fR\^(\|)",

.IR "\fIpoll\fR\^(\|)",

.IR "\fIpselect\fR\^(\|)",

.IR "\fIsend\fR\^(\|)",

.IR "\fIshutdown\fR\^(\|)",

.IR "\fIsocket\fR\^(\|)"

.P

The Base Definitions volume of POSIX.1\(hy2008,

.IR "\fB<sys_socket.h>\fP"

.SH COPYRIGHT

Portions of this text are reprinted and reproduced in electronic form

from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology

-- Portable Operating System Interface (POSIX), The Open Group Base

Specifications Issue 7, Copyright (C) 2013 by the Institute of

Electrical and Electronics Engineers, Inc and The Open Group.

(This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the

event of any discrepancy between this version and the original IEEE and

The Open Group Standard, the original IEEE and The Open Group Standard

is the referee document. The original Standard can be obtained online at

http://www.unix.org/online.html .

Any typographical or formatting errors that appear

in this page are most likely

to have been introduced during the conversion of the source files to

man page format. To report such errors, see

https://www.kernel.org/doc/man-pages/reporting_bugs.html .