.\" Copyright (c) 1983, 1993
.\"	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. 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.
.\"
.\"     @(#)connect.2	8.1 (Berkeley) 6/4/93
.\"
.Dd August 18, 2016
.Dt CONNECT 2
.Os
.Sh NAME
.Nm connect
.Nd initiate a connection on a socket
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In sys/socket.h
.Ft int
.Fn connect "int s" "const struct sockaddr *name" "socklen_t namelen"
.Sh DESCRIPTION
The
.Fa s
argument
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 name ,
which is an address in the communications space of the socket.
.Fa namelen
indicates the amount of space pointed to by
.Fa name ,
in bytes; the
.Fa sa_len
member of
.Fa name
is ignored.
Each communications space interprets the
.Fa name
argument 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 connecting to an invalid address, such as a null address.
.Sh RETURN VALUES
.Rv -std connect
.Sh ERRORS
The
.Fn connect
system call fails if:
.Bl -tag -width Er
.It Bq Er EBADF
The
.Fa s
argument
is not a valid descriptor.
.It Bq Er EINVAL
The
.Fa namelen
argument is not a valid length for the address family.
.It Bq Er ENOTSOCK
The
.Fa s
argument
is a descriptor for a file, not a socket.
.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 EISCONN
The socket is already connected.
.It Bq Er ETIMEDOUT
Connection establishment timed out without establishing a connection.
.It Bq Er ECONNREFUSED
The attempt to connect was forcefully rejected.
.It Bq Er ECONNRESET
The connection was reset by the remote host.
.It Bq Er ENETUNREACH
The network is not reachable from this host.
.It Bq Er EHOSTUNREACH
The remote host is not reachable from this host.
.It Bq Er EADDRINUSE
The address is already in use.
.It Bq Er EFAULT
The
.Fa name
argument specifies an area outside
the process address space.
.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
The connection attempt was interrupted by the delivery of a signal.
The connection will be established in the background,
as in the case of
.Er EINPROGRESS .
.It Bq Er EALREADY
A previous connection attempt has not yet been completed.
.It Bq Er EACCES
An attempt is made to connect to a broadcast address (obtained through the
.Dv INADDR_BROADCAST
constant or the
.Dv INADDR_NONE
return value) through a socket that does not provide broadcast functionality.
.It Bq Er EAGAIN
An auto-assigned port number was requested but no auto-assigned ports
are available.
Increasing the port range specified by
.Xr sysctl 3
MIB variables
.Va net.inet.ip.portrange.first
and
.Va net.inet.ip.portrange.last
may alleviate the problem.
.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 ENOTDIR
A component of the path prefix is not a directory.
.It Bq Er ENAMETOOLONG
A component of a pathname exceeded 255 characters,
or an entire path name exceeded 1023 characters.
.It Bq Er ENOENT
The named socket does not exist.
.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 ELOOP
Too many symbolic links were encountered in translating the pathname.
.It Bq Er EPERM
Write access to the named socket is denied.
.El
.Sh SEE ALSO
.Xr accept 2 ,
.Xr getpeername 2 ,
.Xr getsockname 2 ,
.Xr select 2 ,
.Xr socket 2 ,
.Xr sysctl 3 ,
.Xr sysctl 8
.Sh HISTORY
The
.Fn connect
system call appeared in
.Bx 4.2 .