My OSX quickstart guide to getting a custom chain / testnet up and running.


Install geth

Update brew and install geth - the official golang implementation of the Ethereum protocol.

brew update && brew upgrade

brew tap ethereum/ethereum
brew install ethereum


Create a directory

mkdir ethertest
cd ethertest

./ethertest is where I keep my test setup. From here on out assume all commands are being run from this directory.


Create a test account

First thing you want is an account to hoard our hard earned coins into. Don’t forget the password…

  • Note the two flags:
    • --dev - pre-configured private network with several debugging flags
    • --datadir - This is the directory our blockchain and account keys will live
geth --dev --datadir ./datatest account new

That will spit out an address

Address: {e1afb9ccffe8bc04fe9a35c65c3a3cbff4ef1551}

This is your account address, if you have a look in ./datatest you should find a keystore directory which contains the account key.


This should now be set as the default account, when you fire up a miner this is where all of our ETH will mine to.


Genesis file

Now to get the blockchain setup. I had a bit of trouble here when I was first getting going, a lot of the info available online is bloated with so much shit that it’s hard to follow.

So to make things easy, you want to set a very basic starting point for our blockchain. To do this you need a genesis file.

Create genesis.json

  "config": {
    "chainId": 0,
    "homesteadBlock": 0,
    "eip155Block": 0,
    "eip158Block": 0
  "alloc"      : {},
  "coinbase"   : "0x0000000000000000000000000000000000000000",
  "difficulty" : "0x20000",
  "extraData"  : "",
  "gasLimit"   : "0x2fefd8",
  "nonce"      : "0x0000000000000042",
  "mixhash"    : "0x0000000000000000000000000000000000000000000000000000000000000000",
  "parentHash" : "0x0000000000000000000000000000000000000000000000000000000000000000",
  "timestamp"  : "0x00"

There is quite a bit of info there, I might make another blog post to go over that in the future but for now, that’s all you need.


Blockchain setup

Time to initialise our blockchain.

geth --datadir ./datatest init genesis.json

That should end up outputting Successfully wrote genesis state.

Now run our node in console mode

geth --datadir ./datatest --ipcpath ~/Library/Ethereum/geth.ipc console genesis.json

Note the --ipcpath. If you are using the EthereumWallet app it looks for the ipc file at ~/Library/Ethereum/geth.ipc. So you CANNOT have your ipc file in any other location, it MUST be ~/Library/Ethereum/geth.ipc.

Now you should be sitting at an interactive console running on your private testnet.




Fire up the wallet app, you should see PRIVATE-NET in the top right as it loads.

Watch the ETH roll in.



The console is an easy place to explore. It has tabbed autocompletion so just start typing crap in and see where you end up. e.g.

> miner
  getHashrate: function(),
  setEtherbase: function(),
  setExtra: function(),
  setGasPrice: function(),
  start: function(),
  stop: function()