def _get_version_output(self):
        """
        Ignoring errors, call `ceph --version` and return only the version
        portion of the output. For example, output like::

            ceph version 9.0.1-1234kjd (asdflkj2k3jh234jhg)

        Would return::

            9.0.1-1234kjd
        """
        if not self.executable:
            return ''
        command = [self.executable, '--version']
        out, _, _ = self._check(self.conn, command)
        try:
            return out.decode('utf-8').split()[2]
        except IndexError:
            return ''