The input domain must be value 2(AF_INET), otherwise an error is returned. The input protocol must be value 0, otherwise an error is returned. The input type must be either value 1(SOCK_STREAM) or value 2(SOCK_DGRAM), otherwise an error is returned. Due to this, bitmask flags(such as SOCK_NONBLOCK) for the type field are not supported, therefore the user process when using socket() must use [[SOCU:fcntl]] to support those flag(s).