def set_root_prefix(self, prefix=None):
        """
        Set the prefix to the root environment (default is /opt/anaconda).

        This function should only be called once (right after importing
        conda_api).
        """
        if prefix:
            self.ROOT_PREFIX = prefix
        else:
            # Find some conda instance, and then use info to get 'root_prefix'
            worker = self._call_and_parse(['info', '--json'], abspath=False)
            info = worker.communicate()[0]
            self.ROOT_PREFIX = info['root_prefix']