linux环境安装了lua，但是php中class_exists判断为false，请问我该如何排查？

出错的代码如下，class_exists("Lua",false)为false，我在linux下输入lua，能够调用lua，请问我该如何进一步排查：
public function getTableData($tableName) {
    $gameTable = array();
    if (class_exists("Lua",false)) {
        $lua = new Lua ();
        $lua->eval ( <<<CODE
        function getTable(respath, tablename)
            package.path = respath;
            require("LocalStringToServer");
            return require(tablename);
        end

CODE
);

        $tablePath = GAME_LUA_PATH . "clientData/?.lua;";
        $tablePath .= GAME_LUA_PATH . "serverData/?.lua;";
        $gameTable = $lua->getTable ( $tablePath, $tableName );

    }else {
        exit("lua has not been installed");
    }
    return $gameTable;
}

我重新安装lua就好了，但是还不知道原因在哪里，下次会不会再次出现