CONNECT(2) Linux Programmer's Manual CONNECT(2)
connect - initiate a connection on a socket
int connect(int sockfd, const struct sockaddr *serv_addr, socklen_t
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.
If the connection or binding succeeds, zero is returned. On error, -1
is returned, and errno is set appropriately.
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
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.
Local address is already in use.
The passed address didn't have the correct address family in its
Non-existent interface was requested or the requested address
was not local.
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 ta-
No one listening on the remote address.
EFAULT The socket structure address is outside the user's address
The socket is non-blocking and the connection cannot be com-
pleted 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() com-
pleted successfully (SO_ERROR is zero) or unsuccessfully
(SO_ERROR is one of the usual error codes listed here, explain-
ing the reason for the failure).
EINTR The system call was interrupted by a signal that was caught.
The socket is already connected.
Network is unreachable.
The file descriptor is not associated with a socket.
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.
SVr4, 4.4BSD (the connect() function first appeared in 4.2BSD).
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).
Unconnecting a socket by calling connect() with a AF_UNSPEC address is
not yet implemented.
accept(2), bind(2), getsockname(2), listen(2), path_resolution(2),
Linux 2.6.7 2004-06-23 CONNECT(2)