Updated 2019-10-24

Genesis File

The genesis file contains network configuration items and genesis block parameters.

Configuration Items

Network configuration items are specified in the genesis file in the config object.

Item Description
Chain ID Chain ID for the network
Milestone blocks Milestone blocks for the network
ethash Specifies network uses Ethash and contains fixeddifficulty
clique Specifies network uses Clique and contains Clique configuration items
ibft2 Specifies network uses IBFT 2.0 and contains IBFT 2.0 configuration items
contractSizeLimit Maximum contract size in bytes. Specify in free gas networks. Default is 24576 and the maximum size is 2147483647.
evmStackSize Maximum stack size. Specify to increase the maximum stack size in private networks with very complex smart contracts. Default is 1024.

Genesis Block Parameters

The purpose of some genesis block parameters varies depending on the consensus protocol (Ethash, Clique, or IBFT 2.0). These parameters include:

  • difficulty
  • extraData
  • mixHash

Genesis block parameters with the same purpose across all consensus protocols are described below.

Item Description
coinbase Address to which mining rewards are paid. Can be any value in the genesis block (commonly set to 0x0000000000000000000000000000000000000000).
gasLimit Block gas limit. Total gas limit for all transactions in a block.
nonce Used in block computation. Can be any value in the genesis block (commonly set to 0x0).
timestamp Creation date and time of the block. Must be before the next block so we recommend specifying 0x0 in the genesis file.
alloc Defines accounts with balances or contracts.

Milestone Blocks

In public networks, the milestone blocks specify the blocks at which the network changed protocol.

Ethereum Mainnet Milestone Blocks

{
  "config": {
    ...
    "homesteadBlock": 1150000,
    "daoForkBlock": 1920000,
    "daoForkSupport": true,
    "eip150Block": 2463000,
    "eip150Hash": "0x2086799aeebeae135c246c65021c82b4e15a2c451340993aacfd2751886514f0",
    "eip155Block": 2675000,
    "eip158Block": 2675000,
    "byzantiumBlock": 4370000,
    "constantinopleBlock": 7280000,
    "constantinopleFixBlock": 7280000,
    ...
  },
}

In private networks, the milestone block defines the protocol version for the network.

Private Network Milestone Block

{
  "config": {
    ...
    "constantinopleFixBlock": 0,
    ...
  },
}

Tip

When specifying the milestone block for private networks, you only need to specify the latest milestone because the milestones that precede it are implied.

Fixed Difficulty

Use fixeddifficulty to specify a fixed difficulty in private networks using Ethash.

Example

{
  "config": {
      ...
      "ethash": {
        "fixeddifficulty": 1000
      },

   },
  ...
}