Ethereum genesis block JSON file

Problem

Sometimes, we mistakenly do $ someGeth init somePrivateGenesis.json

then your ~/Library/Ethereum (defaut mainnet datadir in OSX case) genesis block information has been changed.

So you can not use ~/Library/Ethereum for mainnet

How we can fix

$ someGeth --datadir ~/Library/Ethereum init genesis_frontier.json

then your ~/Library/Ethereum can be used again for mainnet. (But needs to wait for finish of reading states).