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.\"	$NetBSD: connect.2,v 1.8 1995/10/12 15:40:48 jtc Exp $
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.\"     @(#)connect.2	8.1 (Berkeley) 6/4/93
.\"
.Dd March 18, 2015
.Dt CONNECT 2
.Os BSD 4.2
.Sh NAME
.Nm connect
.Nd initiate a connection on a socket
.Sh SYNOPSIS
.Fd #include <sys/types.h>
.Fd #include <sys/socket.h>
.Ft int
.Fo connect
.Fa "int socket"
.Fa "const struct sockaddr *address"
.Fa "socklen_t address_len"
.Fc
.Sh DESCRIPTION
The parameter
.Fa socket
is a socket.
If it is of type
.Dv SOCK_DGRAM ,
this call specifies the peer with which the socket is to be associated;
this address is that to which datagrams are to be sent,
and the only address from which datagrams are to be received.
If the socket is of type
.Dv SOCK_STREAM ,
this call attempts to make a connection to
another socket.
The other socket is specified by
.Fa address ,
which is an address in the communications space of the socket.
.Pp
Each communications space interprets the
.Fa address
parameter in its own way.
Generally, stream sockets may successfully
.Fn connect
only once; datagram sockets may use
.Fn connect
multiple times to change their association.
Datagram sockets may dissolve the association
by calling
.Xr disconnectx 2 ,
or by connecting to an invalid address, such as a null address
or an address with 
the address family set to 
.Dv AF_UNSPEC 
(the error 
.Dv EAFNOSUPPORT 
will be harmlessly returned).
.Sh RETURN VALUES
Upon successful completion, a value of 0 is returned.
Otherwise, a value of -1 is returned and the global integer variable
.Va errno
is set to indicate the error.
.Sh ERRORS
The
.Fn connect
system call will fail if:
.Bl -tag -width Er
.\" ==========
.It Bq Er EACCES
The destination address is a broadcast address and the 
socket option 
.Dv SO_BROADCAST 
is not set.
.\" ==========
.It Bq Er EADDRINUSE
The address is already in use.
.\" ==========
.It Bq Er EADDRNOTAVAIL
The specified address is not available on this machine.
.\" ==========
.It Bq Er EAFNOSUPPORT
Addresses in the specified address family cannot be used with this socket.
.\" ==========
.It Bq Er EALREADY
The socket is non-blocking
and a previous connection attempt
has not yet been completed.
.\" ==========
.It Bq Er EBADF
.Fa socket
is not a valid descriptor.
.\" ==========
.It Bq Er ECONNREFUSED
The attempt to connect was ignored
(because the target is not listening for connections)
or explicitly rejected.
.\" ==========
.It Bq Er EFAULT
The
.Fa address
parameter specifies an area outside
the process address space.
.\" ==========
.It Bq Er EHOSTUNREACH
The target host cannot be reached (e.g., down, disconnected).
.\" ==========
.It Bq Er EINPROGRESS
The socket is non-blocking 
and the connection cannot
be completed immediately.
It is possible to
.Xr select 2
for completion by selecting the socket for writing.
.\" ==========
.It Bq Er EINTR
Its execution was interrupted by a signal.
.\" ==========
.It Bq Er EINVAL
An invalid argument was detected
(e.g.,
.Fa address_len
is not valid for the address family,
the specified address family is invalid).
.\" ==========
.It Bq Er EISCONN
The socket is already connected.
.\" ==========
.It Bq Er ENETDOWN
The local network interface is not functioning.
.\" ==========
.It Bq Er ENETUNREACH
The network isn't reachable from this host.
.\" ==========
.It Bq Er ENOBUFS
The system call was unable to allocate a needed memory buffer.
.\" ==========
.It Bq Er ENOTSOCK
.Fa socket
is not a file descriptor for a socket.
.\" ==========
.It Bq Er EOPNOTSUPP
Because
.Fa socket
is listening, no connection is allowed.
.\" ==========
.It Bq Er EPROTOTYPE
.Fa address
has a different type than the socket
that is bound to the specified peer address.
.\" ==========
.It Bq Er ETIMEDOUT
Connection establishment timed out without establishing a connection.
.\" ==========
.It Bq Er ECONNRESET
Remote host reset the connection request.
.El
.Pp
The following errors are specific to connecting names in the UNIX domain.
These errors may not apply in future versions of the UNIX IPC domain.
.Bl -tag -width Er
.\" ==========
.It Bq Er EACCES
Search permission is denied for a component of the path prefix.
.\" ==========
.It Bq Er EACCES
Write access to the named socket is denied.
.\" ==========
.It Bq Er EIO
An I/O error occurred while reading from or writing to the file system.
.\" ==========
.It Bq Er ELOOP
Too many symbolic links were encountered in translating the pathname.
This is taken to be indicative of a looping symbolic link.
.\" ==========
.It Bq Er ENAMETOOLONG
A component of a pathname exceeded 
.Dv {NAME_MAX}
characters, or an entire path name exceeded 
.Dv {PATH_MAX}
characters.
.\" ==========
.It Bq Er ENOENT
The named socket does not exist.
.\" ==========
.It Bq Er ENOTDIR
A component of the path prefix is not a directory.
.El
.Sh LEGACY SYNOPSIS
.Fd #include <sys/types.h>
.Fd #include <sys/socket.h>
.Pp
The include file
.In sys/types.h
is necessary.
.Sh SEE ALSO
.Xr accept 2 ,
.Xr connectx 2 ,
.Xr disconnectx 2 ,
.Xr getsockname 2 ,
.Xr select 2 ,
.Xr socket 2 ,
.Xr compat 5
.Sh HISTORY
The
.Fn connect
function call appeared in
.Bx 4.2 .