Local Ethereum Blockchain

Setting up your Ethereum Node(s)

1. Prereq : Install Geth

$ brew update
$ brew upgrade
$ brew tap ethereum/ethereum
$ brew install ethereum

2. Prereq : create /projects

Create a /projects symbolic link

$ mkdir <my projects folder>
$ sudo ln -s <my projects folder> /projects

3. Create local_ethereum_blockchain folder

$ mkdir /projects/local_ethereum_blockchain

4. Create the genesis block config

Create this file : /projects/local_ethereum_blockchain/genesis.json

With the following contents :

{  
     "config": {
       "chainId": 61,
       "homesteadBlock": 0,
       "eip155Block": 0,
       "eip158Block": 0
                },
     "nonce": "0x0000000000000061",
     "timestamp": "0x0",
     "parentHash": "0x0000000000000000000000000000000000000000000000000000000000000000", 
     "gasLimit": "0x8000000",   
     "difficulty": "0x100",    
     "mixhash": "0x0000000000000000000000000000000000000000000000000000000000000000",
     "coinbase": "0x3333333333333333333333333333333333333333",
     "alloc": {}
}

(info about the genesis file)

5. Initialise an Ethereum node

$ geth --datadir /projects/local_ethereum_blockchain/node1 init /projects/local_ethereum_blockchain/genesis.json

6. Start that Ethereum node

$ geth --datadir /projects/local_ethereum_blockchain/node1 --networkid 4552 console

7. Initialise another Ethereum node

$ geth --datadir /projects/local_ethereum_blockchain/node-2 init /projects/local_ethereum_blockchain/genesis.json

8. Start the 2nd Ethereum node

$ geth --datadir /projects/local_ethereum_blockchain/node-2 --port 30304 --nodiscover --networkid 4552 console

9. Connect one node to the other

In one geth console :

> admin.nodeInfo.enode

In the other console :

> admin.addPeer( <the enode value from the first console> )

Useful geth commands

Node info

> admin.nodeInfo

Peers

Show peers

> admin.peers

How many peers ?

> admin.peers.length

Create an account

You need an account to do be able to do things like mining

> personal.newAccount()

And make sure your remember/save the password!

Unlock account

Neccessary before some actions

> personal.unlockAccount( eth.accounts[0] )

Start mining

> miner.start(1)

The first block may take a while to mine, allow a few minutes

Stop mining

> miner.stop() 

Current block number

> eth.blockNumber

Details of current block

> eth.getBlock( eth.blockNumber ) 

Which node minded the last block

> eth.getBlock(eth.blockNumber).miner

Account balance, in ether

> web3.fromWei(eth.getBalance(eth.accounts[0]))

Transfer ether between accounts

First get the account numbers by doing

> eth.accounts

Then unlock the account you are sending from

> personal.unlockAccount( <from account> )

eg.

> personal.unlockAccount(eth.accounts[0])

Finally transfer 1 ether

> eth.sendTransaction({from: "<from account>", to: "<to account>", value: web3.toWei(1, "ether")})

Exit

> exit

(This will also stop the node from running if it was started using $ geth console (as opposed to $ geth attach))

Connect to other nodes on your network

1. Get the IP of the node : $ ifconfig|grep netmask|awk '{print $2}'

2. Get the enode of the node : > admin.nodeInfo.enode

3. REPLACE [::] in the enode string with the [<ip address>]

4. On your console > admin.addPeer(< the enode string with the ip address in it>)