private function checkSetPrivilege($key)
{
$privilege_field = array('msg_perm.uid', 'msg_perm.gid', 'msg_perm.mode');
if (!\in_array($key, $privilege_field)) {
$message = 'you can only change msg_perm.uid, msg_perm.gid, ' . ' msg_perm.mode and msg_qbytes. And msg_qbytes needs root privileges';
throw new \RuntimeException($message);
}
}