Learn BlockChain Development with me #3: genesis.json explained and start genesis block with Geth

In this post, I am going to share about what genesis.json file is and how you start a private network with Geth. Geth is a Go-Implementation of the Ethereum Protocol.

What Will I Learn?

• What is genesis.json
• How to start your private network with Geth

Requirements

• Geth Installed (if you have not installed Geth, read my previous post)
• basic understanding of blockchain and genesis block
• Preferred UNIX based platform (Linux/Mac)

Difficulty

Intermediate

Tutorial Contents

genesis.json

genesis.json is a JSON file that stores how the genesis block looks like, to initialize your own private blockchain.

The name genesis.json is by convention.

{
  "config": {
    "chainId": 33,
    "homesteadBlock": 0,
    "eip155Block": 0,
    "eip158Block": 0
  },
  "nonce": "0x0000000000000033",
  "timestamp": "0x0",
  "parentHash": "0x0000000000000000000000000000000000000000000000000000000000000000",
  "gasLimit": "0x8000000",
  "difficulty": "0x100",
  "mixhash": "0x0000000000000000000000000000000000000000000000000000000000000000",
  "coinbase": "0x3333333333333333333333333333333333333333",
  "alloc": {}
}

genesis.json

Source

• config - Configuration to describe the chain.
• nonce - Need to be used to initialize the blockchain.
• timestamp - State when was the block generated.
• parentHash - Hash of the entire parent block header.
• gasLimit - Ether require gas to make transaction. However, there is an upper limit for the gas payment. The higher the limit, the more complicated smart contract can be done.
• difficulty - Defines how difficult to mine a new block.
• mixhash - combined with nonce.
• coinbase - Your address.
• alloc - Preallocated Ether accounts

To read more about details of each of the parameters, check out this stackexchange answer.

Create a Genesis Block

The directory currently look like this:

/
|- genesis.json

Run geth --datadir=./chaindata/ init ./genesis.json to generate the chaindata which will set genesis block for your chain.

It will generate a chaindata file. From there, run geth --datadir=./chaindata/ to start the geth

Then the private network has started.

Now, look for the ipc (for mac/linux) location.

INFO [01-31|11:39:40] IPC endpoint opened: /Volumes/HDD/files/blockchain/ethereum/chaindata/geth.ipc

You have successfully created a genesis block! In the next tutorial, I will share about getting started with EthereumTestRPC NPM library.

Curriculum

1. #1: Introduction to Blockchain and Smart Contract
2. #2: Ethereum Node and Install Development tools

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