After Geth is installed, it can be configured to run locally without connecting to any network on the internet. Every chain and network has a genesis block or the first block. This block does not have any parent and is the first block of the chain. A genesis.json file is required to create this first block. A sample genesis.json file is shown in the following code snippet:
{ "config": {"chainId": 15,"homesteadBlock": 0,"eip155Block": 0,"eip158Block": 0},"nonce": "0x0000000000000042","mixhash": "0x0000000000000000000000000000000000000000000000000000000000000000","difficulty": "0x200","alloc": {},"coinbase": "0x0000000000000000000000000000000000000000","timestamp": "0x00","parentHash": "0x0000000000000000000000000000000000000000000000000000000000000000", ...
