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Date of last update: September 12, 2022

Genesis file

The genesis file defines the first block in the chain, and the first block defines which chain you want to join.

For Ethereum Mainnet and public testnets (for example, Goerli) the genesis configuration definition is in Besu and used when specifying a public network using the --network command line option.

For private networks, create a JSON genesis file, then specify the genesis file using the --genesis-file command line option.

The genesis file specifies the network-wide settings, such as those for a free gas network, so all nodes in a network must use the same genesis file.


You can specify node-level settings on the command line or in the node configuration file.

Example IBFT 2.0 genesis file

  "config": {
    "chainId": 2018,
    "berlinBlock": 0,
    "ibft2": {
      "blockperiodseconds": 2,
      "epochlength": 30000,
      "requesttimeoutseconds": 4
  "nonce": "0x0",
  "timestamp": "0x58ee40ba",
  "extraData": "0xf83ea00000000000000000000000000000000000000000000000000000000000000000d5949811ebc35d7b06b3fa8dc5809a1f9c52751e1deb808400000000c0",
  "gasLimit": "0x1fffffffffffff",
  "difficulty": "0x1",
  "mixHash": "0x63746963616c2062797a616e74696e65206661756c7420746f6c6572616e6365",
  "coinbase": "0x0000000000000000000000000000000000000000",
  "alloc": {
    "9811ebc35d7b06b3fa8dc5809a1f9c52751e1deb": {
      "balance": "0xad78ebc5ac6200000"