code: func (cli *Client) ContainerExecStart(ctx context.Context, execID string, config types.ExecStartCheck) error {
  	resp, err := cli.post(ctx, "/exec/"+execID+"/start", nil, config, nil)
  	ensureReaderClosed(resp)
  	return err
  }
docs: // ContainerExecStart starts an exec process already created in the docker host.