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.\" Copyright 1993 Rickard E. Faith (faith@cs.unc.edu)
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.\" 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@gmail.com>
.\"
-.TH CONNECT 2 2004-06-23 "Linux" "Linux Programmer's Manual"
+.TH CONNECT 2 2019-03-06 "Linux" "Linux Programmer's Manual"
.SH NAME
connect \- initiate a connection on a socket
.SH SYNOPSIS
.BR "#include <sys/types.h>" " /* See NOTES */"
.br
.B #include <sys/socket.h>
-.sp
-.BI "int connect(int " sockfd ", const struct sockaddr *" serv_addr ,
+.PP
+.BI "int connect(int " sockfd ", const struct sockaddr *" addr ,
.BI " socklen_t " addrlen );
.fi
.SH DESCRIPTION
system call connects the socket referred to by the file descriptor
.I sockfd
to the address specified by
-.IR serv_addr .
+.IR addr .
The
-.IR addrlen
+.I addrlen
argument specifies the size of
-.IR serv_addr .
+.IR addr .
The format of the address in
-.I serv_addr
+.I addr
is determined by the address space of the socket
.IR sockfd ;
see
.BR socket (2)
for further details.
-
+.PP
If the socket
.I sockfd
is of type
-.B SOCK_DGRAM
+.BR SOCK_DGRAM ,
then
-.I serv_addr
+.I 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
.BR SOCK_SEQPACKET ,
this call attempts to make a connection to the socket that is bound
to the address specified by
-.IR serv_addr .
+.IR addr .
.PP
Generally, connection-based protocol sockets may successfully
.BR connect ()
member of
.I sockaddr
set to
-.BR AF_UNSPEC .
-.SH "RETURN VALUE"
+.BR AF_UNSPEC
+(supported on Linux since kernel 2.2).
+.SH RETURN VALUE
If the connection or binding succeeds, zero is returned.
On error, \-1 is returned, and
.I errno
There may be other domain-specific error codes.
.TP
.B EACCES
-For Unix domain sockets, which are identified by pathname:
+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
.BR path_resolution (7).)
.TP
-.B EACCES, EPERM
+.BR 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.
.B EADDRINUSE
Local address is already in use.
.TP
+.B EADDRNOTAVAIL
+(Internet domain sockets)
+The socket referred to by
+.I 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
+.I /proc/sys/net/ipv4/ip_local_port_range
+in
+.BR ip (7).
+.TP
.B EAFNOSUPPORT
The passed address didn't have the correct address family in its
.I sa_family
field.
.TP
.B EAGAIN
-No more free local ports or insufficient entries in the routing cache.
-For
-.B PF_INET
-see the
-.I net.ipv4.ip_local_port_range
-sysctl in
-.BR ip (7)
-on how to increase the number of local ports.
+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.
.TP
.B EALREADY
-The socket is non-blocking and a previous connection attempt has not yet
+The socket is nonblocking and a previous connection attempt has not yet
been completed.
.TP
.B EBADF
-The file descriptor is not a valid index in the descriptor table.
+.I sockfd
+is not a valid open file descriptor.
.TP
.B ECONNREFUSED
-No one listening on the remote address.
+A
+.BR connect ()
+on a stream socket found no one listening on the remote address.
.TP
.B EFAULT
The socket structure address is outside the user's address space.
.TP
.B EINPROGRESS
-The socket is non-blocking and the connection cannot be completed
-immediately.
+The socket is nonblocking and the connection cannot be completed immediately.
+(UNIX domain sockets failed with
+.BR EAGAIN
+instead.)
It is possible to
.BR select (2)
or
explaining the reason for the failure).
.TP
.B EINTR
-The system call was interrupted by a signal that was caught.
+The system call was interrupted by a signal that was caught; see
+.BR signal (7).
.\" For TCP, the connection will complete asynchronously.
.\" See http://lkml.org/lkml/2005/7/12/254
.TP
Network is unreachable.
.TP
.B ENOTSOCK
-The file descriptor is not associated with a socket.
+The file descriptor
+.I sockfd
+does not refer to a socket.
+.TP
+.B EPROTOTYPE
+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.
.TP
.B ETIMEDOUT
Timeout while attempting connection.
busy to accept new connections.
Note that for IP sockets the timeout may
be very long when syncookies are enabled on the server.
-.SH "CONFORMING TO"
-SVr4, 4.4BSD, (the
-.BR connect ()
-function first appeared in 4.2BSD), POSIX.1-2001.
+.SH CONFORMING TO
+POSIX.1-2001, POSIX.1-2008, SVr4, 4.4BSD,
+.RB (connect ()
+first appeared in 4.2BSD).
.\" SVr4 documents the additional
.\" general error codes
.\" .BR EADDRNOTAVAIL ,
.\" It also
.\" documents many additional error conditions not described here.
.SH NOTES
-POSIX.1-2001 does not require the inclusion of
+POSIX.1 does not require the inclusion of
.IR <sys/types.h> ,
and this header file is not required on Linux.
However, some historical (BSD) implementations required this header
file, and portable applications are probably wise to include it.
-
-The third argument of
-.BR connect ()
-is in reality an
-.I int
-(and this is what 4.x BSD and libc4 and libc5 have).
-Some POSIX confusion resulted in the present
-.IR socklen_t ,
-also used by glibc.
-See also
+.PP
+For background on the
+.I socklen_t
+type, see
.BR accept (2).
-.SH BUGS
-Unconnecting a socket by calling
+.PP
+If
.BR connect ()
-with a
-.B AF_UNSPEC
-address is not yet implemented.
+fails, consider the state of the socket as unspecified.
+Portable applications should close the socket and create a new one for
+reconnecting.
.SH EXAMPLE
An example of the use of
.BR connect ()
is shown in
.BR getaddrinfo (3).
-.SH "SEE ALSO"
+.SH SEE ALSO
.BR accept (2),
.BR bind (2),
.BR getsockname (2),
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