# start() Start the underlying Tor instance. ``` func start() async throws ``` ## Discussion In a production conformer this creates the data directory, hands `torrc`-equivalent configuration to `tor_main_configuration_new()`, runs `tor_run_main()` on a dedicated background thread, and resolves once the embedded control socket is reachable — but **before** the Tor network bootstrap has made progress. Pair with [`waitUntilBootstrapped(timeout:)`](/documentation/Tor/TorSession/waitUntilBootstrapped(timeout:)) to block until Tor is actually usable for relaying traffic. Mock conformers typically resolve this immediately or fail fast per their test scenario. > Throws: An implementation-defined error if the instance cannot be > started. Production conformer throws ``doc://Tor/documentation/Tor/TorError/alreadyStarted`` > if invoked while Tor is running or starting, and > ``doc://Tor/documentation/Tor/TorError/startFailed(_:)`` if `tor_run_main()` returns an error.