# Host-mode background processes

Host jobs clean up background step processes at job completion. A step can opt out:

```yaml
steps:
  - name: Start shared helper
    env:
      RUNNER_TRACKING_ID: ""
    run: Start-Process vendor-helper.exe
```

- Set the `RUNNER_TRACKING_ID` override in the step's `env` before it starts. Any value different from the job's ID opts out, including an empty string. On Linux and macOS a script can also set it before starting a process.
- Opted-out processes and descendants that inherit the override survive normal job cleanup and expired output waits. Detach helper output because the runner closes leftover output pipes after a bounded wait.
- Cancelling or timing out an active step still terminates its process tree.
- The override does not preserve workspace or temporary files. Store persistent helper files outside those directories and arrange the helper's eventual shutdown.

This follows [actions/runner's tracking ID and orphan cleanup](https://github.com/actions/runner/blob/main/src/Runner.Worker/JobExtension.cs). Container jobs follow their container's lifecycle.