Not sure how relevant this is, but the length you give to connect as third parameter should be the actual *used* length of the structure, i.e. not sizeof(sun) but rather sizeof(sun.sun_family) + strlen(sun.sun_path). Also, are you sure that the listening sockets have been created? Also, instead of just saying if(connect(...) < 0) printf("error") use the perror() function, so that you get the exact reason why connect() failed. $ man 2 connect Code: 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_range ip(7) for information on how to increase the number of local ports. EALREADY The socket is nonblocking 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 nonblocking 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. That may help you debugging the problem.
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_range ip(7) for information on how to increase the number of local ports. EALREADY The socket is nonblocking 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 nonblocking 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.