connect(2) System Calls Manual connect(2) connect - (libc -lc) #include int connect(int sockfd, const struct sockaddr *addr, socklen_t addrlen); connect() sockfd addr. addrlen addr. addr sockfd socket(2) . sockfd SOCK_DGRAM addr . SOCK_STREAM SOCK_SEQPACKET addr. ( UNIX) connect() . ( UNIX ) connect() . ( TCP UNIX ) sa_family sockaddr AF_UNSPEC . (AF_UNSPEC Linux 2.2.) . -1 errno . . . EACCES UNIX : . ( path_resolution(7).) EACCES EPERM . EACCES SELinux ( HTTP HTTP ). EADDRINUSE . EADDRNOTAVAIL ( ) sockfd (ephemeral) . /proc/sys/net/ipv4/ip_local_port_range ip(7). EAFNOSUPPORT sa_family . EAGAIN UNIX . . EALREADY . EBADF sockfd . ECONNREFUSED connect() . EFAULT . EINPROGRESS . ( UNIX EAGAIN .) select(2) poll(2) . select(2) getsockopt(2) SO_ERROR SOL_SOCKET connect() (SO_ERROR ) (SO_ERROR ). EINTR signal(7). EISCONN . ENETUNREACH . ENOTSOCK sockfd . EPROTOTYPE . UNIX . ETIMEDOUT . . IP . addr.sun_path null AF_UNIX. POSIX.1-2024. POSIX.1-2001 SVr4 4.2BSD. connect() . . connect() getaddrinfo(3). accept(2), bind(2), getsockname(2), listen(2), socket(2), path_resolution(7), selinux(8) 3 . . : . 6.18 8 2026 connect(2)