--- title: Start Besu sidebar_position: 3 description: Start Besu on a public Ethereum network. --- > For AI agents: a documentation index is available at [/llms.txt](/llms.txt). Append `.md` to any documentation URL to get the markdown source. import Tabs from '@theme/Tabs'; import TabItem from '@theme/TabItem'; # Start Besu Nodes can connect to Ethereum Mainnet, [Linea](https://docs.linea.build/get-started/how-to/run-a-node), and their respective public testnets. Use the [`besu`](../reference/cli/options.md) command with the required command line options to start a node. ## Prerequisites [Besu installed](install/binary-distribution.md) ## Local block data When connecting to a network other than the network previously connected to, you must either delete the local block data or use the [`--data-path`](../reference/cli/options.md#data-path) option to specify a different data directory. To delete the local block data, delete the `database` directory in the `besu/build/distribution/besu-` directory. ## Genesis configuration Besu specifies the genesis configuration, and sets the network ID and bootnodes when connecting to [ETH testnets](#run-a-node-on-an-ethereum-testnet), and [Mainnet](#run-a-node-on-ethereum-mainnet). :::info The following networks and testnets are deprecated: ETC (Ethereum Classic) and Mordor. ::: When you specify [`--network=dev`](../reference/cli/options.md#network), Besu uses the development mode genesis configuration with a fixed low difficulty. A node started with [`--network=dev`](../reference/cli/options.md#network) has an empty bootnodes list by default. The genesis files defining the genesis configurations are in the [Besu source files](https://github.com/hyperledger/besu/tree/master/config/src/main/resources). To define a genesis configuration, create a genesis file (for example, `genesis.json`) and specify the file using the [`--genesis-file`](../reference/cli/options.md#genesis-file) option. ## Syncing and storage By default, Besu syncs to the current state of the blockchain using [snap sync](../concepts/node-sync.md#snap-synchronization) in: - Networks specified using [`--network`](../reference/cli/options.md#network) except for the `dev` development network. - Ethereum Mainnet. We recommend using [snap sync](../concepts/node-sync.md#snap-synchronization) for a faster sync, by starting Besu with [`--sync-mode=SNAP`](../reference/cli/options.md#sync-mode). By default, Besu stores data in the [Bonsai Tries format](../concepts/data-storage-formats.md#bonsai-tries). ## Run a node for testing To run a node that mines blocks at a rate suitable for testing purposes: ```bash besu --network=dev --rpc-http-cors-origins="all" --host-allowlist="*" --rpc-ws-enabled --rpc-http-enabled --data-path=/tmp/tmpDatdir ``` You can also use the following [configuration file](../how-to/configure-besu/index.md) on the command line to start a node with the same options as above: ```toml network="dev" rpc-http-cors-origins=["all"] host-allowlist=["*"] rpc-ws-enabled=true rpc-http-enabled=true data-path="/tmp/tmpdata-path" ``` :::danger Warning The following settings are a security risk in production environments: - Enabling the HTTP JSON-RPC service ([`--rpc-http-enabled`](../reference/cli/options.md#rpc-http-enabled)) and setting [`--rpc-http-host`](../reference/cli/options.md#rpc-http-host) to 0.0.0.0 exposes the RPC connection on your node to any remote connection. - Setting [`--host-allowlist`](../reference/cli/options.md#host-allowlist) to `"*"` allows JSON-RPC API access from any host. - Setting [`--rpc-http-cors-origins`](../reference/cli/options.md#rpc-http-cors-origins) to `"all"` or `"*"` allows cross-origin resource sharing (CORS) access from any domain. ::: ## Run a node on an Ethereum testnet To run a node on [Hoodi](https://github.com/eth-clients/hoodi) specifying a data directory: ```bash besu --network=hoodi --data-path=/ ``` Where `` and `` are the path and directory to save the Hoodi chain data to. To run a node on [Sepolia](https://github.com/eth-clients/sepolia) specifying a data directory: ```bash besu --network=sepolia --data-path=/ ``` Where `` and `` are the path and directory to save the Sepolia chain data to. To run a node on [Ephemery](https://github.com/ephemery-testnet/ephemery-resources?tab=readme-ov-file) specifying a data directory: ```bash besu --network=ephemery --data-path=/ ``` Where `` and `` are the path and directory to save the Ephemery chain data to. See the [guide on connecting to a testnet](connect/testnet.md) for more information. ## Run a node on Ethereum Mainnet To run a node on the Ethereum Mainnet: ```bash besu ``` To run a node on Mainnet with the HTTP JSON-RPC service enabled and available for localhost only: ```bash besu --rpc-http-enabled ``` See the [guide on connecting to Mainnet](connect/mainnet.md) for more information. ## Confirm node is running If you started Besu with the [`--rpc-http-enabled`](../reference/cli/options.md#rpc-http-enabled) option, use [cURL](https://curl.haxx.se/) to call [JSON-RPC API methods](../reference/api/index.md) to confirm the node is running. - `eth_chainId` returns the chain ID of the network. ```bash curl -X POST --data '{"jsonrpc":"2.0","method":"eth_chainId","params":[],"id":1}' localhost:8545/ -H "Content-Type: application/json" ``` - `eth_syncing` returns the starting, current, and highest block. ```bash curl -X POST --data '{"jsonrpc":"2.0","method":"eth_syncing","params":[],"id":1}' localhost:8545/ -H "Content-Type: application/json" ``` For example, after connecting to Mainnet, `eth_syncing` will return something similar to: ```json { "jsonrpc": "2.0", "id": 1, "result": { "startingBlock": "0x0", "currentBlock": "0x2d0", "highestBlock": "0x66c0" } } ```