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.
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(2).)
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
PF_INET see the
net.ipv4.ip_local_port_range sysctl in
ip(7)
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.
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.
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).
