an unknown filter was not added: includes 的解决办法

今天偶尔发现linode的服务器出现错误，致使apache2停止响应，代码如下：

[Tue Sep 11 23:55:05 2012] [error] an unknown filter was not added: includes
[Tue Sep 11 23:56:22 2012] [error] an unknown filter was not added: includes
[Tue Sep 11 23:56:58 2012] [error] an unknown filter was not added: includes
[Wed Sep 12 00:02:14 2012] [notice] caught SIGTERM, shutting down

在网上查了好久，发现需要启用apache2的include模块，挺怪的问题，以前没有遇到过
运行：

sudo a2enmod include

即可