The file descriptor
sockfd must refer to a socket.
If the socket is of type
SOCK_DGRAM then the
serv_addr address 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 another socket. The other
socket is specified by
serv_addr , which is an address (of length
addrlen ) in the communications space of the socket. Each
communications space interprets the
serv_addr parameter in its own way.
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 .
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.
EBADF
The file descriptor is not a valid index in the descriptor table.
EFAULT
The socket structure address is outside the user's address space.
ENOTSOCK
The file descriptor is not associated with a socket.
EISCONN
The socket is already connected.
ECONNREFUSED
No one listening on the remote address.
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.
ENETUNREACH
Network is unreachable.
EADDRINUSE
Local address is already in use.
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 indicates writability, use
getsockopt(2) to read the
SO_ERROR option at level
SOL_SOCKET to determine whether
connect completed successfully
is zero) or unsuccessfully
is one of the usual error codes listed here,
explaining the reason for the failure).
EALREADY
The socket is non-blocking and a previous connection attempt has not yet
been completed.
EAGAIN
No more free local ports or insufficient entries in the routing cache. For
PF_INET see the
net.ipv4.ip_local_port_range sysctl in
ip(7) on how to increase the number of local ports.
EAFNOSUPPORT
The passed address didn't have the correct address family in its
sa_family field.
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.
CONFORMING TO
SVr4, 4.4BSD (the
connect function first appeared in BSD 4.2). SVr4 documents the additional
general error codes
EADDRNOTAVAIL , EINVAL , EAFNOSUPPORT , EALREADY , EINTR , EPROTOTYPE , and
ENOSR . It also
documents many additional error conditions not described here.
NOTE
The third argument of
connect is in reality an int (and this is what BSD 4.* and libc4 and libc5 have).
Some POSIX confusion resulted in the present socklen_t.
The draft standard has not been adopted yet, but glibc2 already
follows it and also has socklen_t. See also
accept(2) .
BUGS
Unconnecting a socket by calling
connect with a
AF_UNSPEC address is not yet implemented.
