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book/src/interop-cli.md

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+# Interop CLI Overview
+
+The Lighthouse CLI has two primary tasks:
+
+- **Resuming** an existing database with `$ ./beacon_node`.
+- **Creating** a new testnet database using `$ ./beacon_node testnet`.
+
+_See [Scenarios](./interop-scenarios.md) for methods we're likely to use
+during interop._
+
+## Creating a new database
+
+There are several methods for creating a new beacon node database:
+
+- `quick`: using the `(validator_client, genesis_time)` tuple.
+- `recent`: as above but `genesis_time` is set to the start of some recent time
+	window.
+- `file`: loads the genesis file from disk in one of multiple formats.
+- `bootstrap`: a Lighthouse-specific method where we connect to a running node
+	and download it's specification and genesis state via the HTTP API.
+
+See `$ ./beacon_node testnet --help` for more detail.
+
+## Resuming from an existing database
+
+Once a database has been created, it can be resumed by running `$ ./beacon_node`.
+
+Presently, this command will fail if no existing database is found. You must
+use the `$ ./beacon_node testnet` command to create a new database.