CONNECT(2) Linux Programmer's Manual CONNECT(2) NAME connect - initiate a connection on a socket(2,7,n) SYNOPSIS #include <sys/types.h> #include <sys/socket.h> int connect(int sockfd, const struct sockaddr *serv_addr, socklen_t addrlen); DESCRIPTION The file(1,n) descriptor sockfd must refer to a socket. If the socket(2,7,n) 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 data- grams are received. If the socket(2,7,n) is of type SOCK_STREAM or SOCK_SEQ- PACKET, this call attempts to make a connection to another socket. The other socket(2,7,n) is specified by serv_addr, which is an address (of length addrlen) in(1,8) the communications space of the socket. Each communica- tions space interprets the serv_addr parameter in(1,8) 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(7,n,1 builtins) to AF_UNSPEC. RETURN VALUE If the connection or binding succeeds, zero is returned. On error(8,n), -1 is returned, and errno is set(7,n,1 builtins) appropriately. ERRORS The following are general socket(2,7,n) errors only. There may be other domain-specific error(8,n) codes. EACCES For Unix domain sockets, which are identified by pathname: Write permission is denied on the socket(2,7,n) file(1,n), or search permission is denied for one of the directories in(1,8) the path prefix. (See also path_resolution(2).) EACCES, EPERM The user tried to connect to a broadcast address without having the socket(2,7,n) broadcast flag enabled or the connection request failed because of a local firewall rule. EADDRINUSE Local address is already in(1,8) use. EAFNOSUPPORT The passed address didn't have the correct address family in(1,8) its sa_family field. EAGAIN No more free local ports or insufficient entries in(1,8) the routing cache. For PF_INET see the net.ipv4.ip_local_port_range sysctl(2,5,8) in(1,8) ip(7,8)(7) on how to increase the number of local ports. EALREADY The socket(2,7,n) is non-blocking and a previous connection attempt has not yet been completed. EBADF The file(1,n) descriptor is not a valid index in(1,8) the descriptor ta- ble. ECONNREFUSED No one listening on the remote address. EFAULT The socket(2,7,n) structure address is outside the user's address space. EINPROGRESS The socket(2,7,n) is non-blocking and the connection cannot be com- pleted immediately. It is possible to select(2,7,2 select_tut)(2) or poll(2) for completion by selecting the socket(2,7,n) for writing. After select(2,7,2 select_tut) indicates writability, use getsockopt(2) to read(2,n,1 builtins) 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(8,n) codes listed here, explain- ing the reason for the failure). EISCONN The socket(2,7,n) is already connected. ENETUNREACH Network is unreachable. ENOTSOCK The file(1,n) descriptor is not associated with a socket. ETIMEDOUT Timeout while attempting connection. The server may be too busy to accept(2,8) new connections. Note that for IP sockets the timeout(1,3x,3x cbreak) may be very long when syncookies are enabled on the server. CONFORMING TO SVr4, 4.4BSD (the connect function first appeared in(1,8) BSD 4.2). SVr4 documents the additional general error(8,n) codes EADDRNOTAVAIL, EINVAL, EAFNOSUPPORT, EALREADY, EINTR, EPROTOTYPE, and ENOSR. It also docu- ments many additional error(8,n) conditions not described here. NOTE The third argument of connect is in(1,8) reality an int (and this is what BSD 4.* and libc4 and libc5 have). Some POSIX confusion resulted in(1,8) the present socklen_t, also used by glibc. See also accept(2,8)(2). BUGS Unconnecting a socket(2,7,n) by calling connect with a AF_UNSPEC address is not yet implemented. SEE ALSO accept(2,8)(2), bind(2,n,1 builtins)(2), getsockname(2), listen(1,2,7)(2), path_resolution(2), socket(2,7,n)(2) Linux 2.6.7 2004-06-23 CONNECT(2)