> ## Documentation Index
> Fetch the complete documentation index at: https://docs.optimism.io/llms.txt
> Use this file to discover all available pages before exploring further.

# Legacy Geth configuration

> Learn how to configure Legacy Geth for serving historical execution traces on upgraded OP Stack networks.

Legacy Geth (`l2geth`) is required only for upgraded networks like OP Mainnet to serve historical execution traces from before the Bedrock upgrade.
If you're running a node that had a chain genesis after the Bedrock upgrade, you do not need Legacy Geth.

## Historical execution vs. historical data routing

Only requests for historical execution will be routed to Legacy Geth.
Everything else will be served by `op-geth` directly.
The term *historical execution* refers to RPC methods that need to execute transactions prior to bedrock (not just read data from the database):

* `eth_call`
* `eth_estimateGas`
* `debug_traceBlockByNumber`
* `debug_traceBlockByHash`
* `debug_traceCall`
* `debug_traceTransaction`

If you do not need these RPC methods for historical data, then you do not need to run Legacy Geth at all.

## What is Legacy Geth?

Legacy Geth is the old `l2geth` binary running against a preconfigured data directory.
It serves historical execution data from before the Bedrock upgrade.

## Setup

### 1. Download the preconfigured data directory

Download and extract the Legacy Geth data directory, which is available at [datadirs.optimism.io](https://datadirs.optimism.io).

```bash theme={null}
# Download the data directory
curl -o legacy-geth-datadir.tar -sL <URL-to-legacy-datadir>

# Extract it
tar -xvf legacy-geth-datadir.tar -C /data/legacy-geth
```

### 2. Configure Legacy Geth

Run Legacy Geth with the minimum required configuration:

```bash theme={null}
USING_OVM=true \
  ETH1_SYNC_SERVICE_ENABLE=false \
  RPC_API=eth,rollup,net,web3,debug \
  RPC_ADDR=0.0.0.0 \
  RPC_CORS_DOMAIN=* \
  RPC_ENABLE=true \
  RPC_PORT=8545 \
  RPC_VHOSTS=* \
  geth --datadir /data/legacy-geth
```

<Warning>
  It is imperative that you specify the `USING_OVM=true` environment variable.
  Failing to specify this will cause `l2geth` to return invalid execution traces or panic at startup.
</Warning>

### 3. Configure op-geth to route to Legacy Geth

Update your op-geth configuration to route historical requests to Legacy Geth:

```bash theme={null}
geth \
  --datadir=/data/optimism \
  --rollup.historicalrpc=http://localhost:8545 \
  # ... other flags
```

The `--rollup.historicalrpc` flag tells op-geth where to route requests for historical execution.

## Environment variables

Legacy Geth accepts the following environment variables:

| Variable                   | Description                    | Default                               |
| -------------------------- | ------------------------------ | ------------------------------------- |
| `USING_OVM`                | **Required**. Enables OVM mode | N/A (must be set to `true`)           |
| `ETH1_SYNC_SERVICE_ENABLE` | Enables L1 sync service        | `true` (set to `false` for read-only) |
| `RPC_API`                  | Enabled RPC APIs               | `eth,net,web3`                        |
| `RPC_ADDR`                 | RPC listening address          | `localhost`                           |
| `RPC_CORS_DOMAIN`          | CORS domains                   | `localhost`                           |
| `RPC_ENABLE`               | Enable RPC server              | `false`                               |
| `RPC_PORT`                 | RPC port                       | `8545`                                |
| `RPC_VHOSTS`               | Virtual hosts                  | `localhost`                           |

## Historical execution vs. historical data

Only requests for **historical execution** will be routed to Legacy Geth.
Everything else will be served by op-geth directly.

### Historical execution RPC methods

These methods require transaction execution and are routed to Legacy Geth for pre-Bedrock blocks:

* `eth_call`
* `eth_estimateGas`
* `debug_traceBlockByNumber`
* `debug_traceBlockByHash`
* `debug_traceCall`
* `debug_traceTransaction`

### Historical data RPC methods

These methods only read data from the database and are served by op-geth:

* `eth_getBlockByNumber`
* `eth_getBlockByHash`
* `eth_getTransactionByHash`
* `eth_getTransactionReceipt`
* `eth_getLogs`

## Troubleshooting

<Warning>
  `l2geth` is based on an old version of geth where trace functionality is unstable.
  It is no longer maintained and will not be updated.
</Warning>

### Legacy Geth won't start

**Problem**: `l2geth` panics or returns errors on startup

**Solution**: Ensure `USING_OVM=true` is set in your environment variables

### Invalid execution traces

**Problem**: Legacy Geth returns invalid or incorrect trace data

**Solution**: Verify that `USING_OVM=true` is set and the data directory is complete and uncorrupted

### op-geth not routing to Legacy Geth

**Problem**: Historical execution requests are not being routed to Legacy Geth

**Solution**: Check that `--rollup.historicalrpc` is set on op-geth with the correct URL to Legacy Geth