I study EOS have a peroid of time, At begining use the version of 2018-02-14, everything is well. several days ago, update to v3.0.0, and encounter a lot of errors, almost break me down. Now make a note, hope can give a little help to these who meet the same problem, and EOS can settle this bug as soon.
1) build
git clone https://github.com/eosio/eos --recursive
cd eos
./eosio_build.sh
there, meet the first error. install Mongodb timeout. this error is because I use ubuntu virtual machine, and set nat can be resolved by set the virtual machine Network Address Translation(nat), then it can build success.
2) I build smart contract hello which completely same as officail given. It occur "fatal error eosiolib/eosio.hpp" . I change the include mode from "<eosiolib/eosio>" to ""eosio"" it works,.
3) when update smart contract, "account.code_version != code_id: contract is already running this version of code"
it because I only change the abi file, add no function code print to cpp file, regenerate wast abi file,everything ok.