Subclasses can override to provide special
            environment setup, command prefixes, etc.

def check_output(self, cmd, timeout=None, keep_rc=False, env=None):
        """ Subclasses can override to provide special
            environment setup, command prefixes, etc.
        """
        return subproc.call(cmd, timeout=timeout or self.timeout,
                keep_rc=keep_rc, env=env)