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
(supported on Linux since kernel 2.2).
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
AF_INET
see the description of
/proc/sys/net/ipv4/ip_local_port_rangeip(7)
for information 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; see
signal(7).
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
POSIX.1-2001 does not require the inclusion of
<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
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).
EXAMPLE
An example of the use of
connect()
is shown in
getaddrinfo(3).
This page is part of release 3.14 of the Linux
man-pages
project.
A description of the project,
and information about reporting bugs,
can be found at
http://www.kernel.org/doc/man-pages/.
