Custom genesis

What is genesis file

Genesis file is a database file containing Genesis Block. It contains all the transactions from the Ether sale, and when a user inputs it into the client, it represents their decision to join the network under its terms: it is the first step to consensus.

Genesis files for Frontier and Morden testnets are available here

You can select which genesis to load by specifying profile parameter on pyethapp startup:

pyethapp --profile morden run

Custom genesis

It is possible to load custom genesis allocation in pyethapp. Genesis format is a json and might look like this:

{
  "nonce": "0x0000000000000042",
  "difficulty": "0x400000000",
  "mixhash": "0x0000000000000000000000000000000000000000000000000000000000000000",
  "coinbase": "0x0000000000000000000000000000000000000000",
  "timestamp": "0x00",
  "parentHash": "0x0000000000000000000000000000000000000000000000000000000000000000",
  "extraData": "0x11bbe8db4e347b4e8c937c1c8370e4b5ed33adb3db69cbdb7a38e1e50b1b82fa",
  "gasLimit": "0x1388",
  "alloc": {
    "3282791d6fd713f1e94f4bfd565eaa78b3a0599d": {
      "balance": "1337000000000000000000"
    },
    "17961d633bcf20a7b029a7d94b7df4da2ec5427f": {
      "balance": "229427000000000000000"
    }
  }
}

How to load custom genesis

There are 3 ways to load custom genesis in pyethapp:

1. Save genesis json as a file (e.g mygenesis.json) and use -c and eth.genesis:

   $ pyethapp -c eth.genesis=mygenesis.json run
   

2. Pass genesis json as a string using -c and eth.genesis argument:

   $ pyethapp -c eth.genesis='{"nonce":"0x0000000000000042","difficulty":"0x400000000","mixhash":"0x0000000000000000000000000000000000000000000000000000000000000000","coinbase":"0x0000000000000000000000000000000000000000","timestamp":"0x00","parentHash":"0x0000000000000000000000000000000000000000000000000000000000000000","extraData":"0x11bbe8db4e347b4e8c937c1c8370e4b5ed33adb3db69cbdb7a38e1e50b1b82fa","gasLimit":"0x1388","alloc":{"3282791d6fd713f1e94f4bfd565eaa78b3a0599d":{"balance":"1337000000000000000000"},"17961d633bcf20a7b029a7d94b7df4da2ec5427f":{"balance":"229427000000000000000"}}}' run
   

3. Put genesis json in a config file (e.g. myconfig.yaml) and use -C / --Config to run pyethapp with that configuration instead of default one ~/.config/pyethapp/config.yaml

   $ pyethapp -C myconfig.yaml run 

or

```console
$ pyethapp --Config myconfig.yaml run 
```

`myconfig.yaml` might look like:

```console
accounts:
  privkeys_hex: [482580fe05668c54ed16708d17481cf6546be6faca24d4b80919a6ef5ed95c92]
node: {privkey_hex: 7c4a6bc6367dd0cfe27848a1da86ac4f0c5f947f4eefb857ed58728147778d89}
eth:
  genesis: PUT_YOUR_GENESIS_JSON_HERE
```

References

Refer sample genesis files for genesis json format.

Refer Configuring for more details on custom configuration.

You might also find test_app.py helpful to see how custom config can be passed to the app.