昨天我在博客上转贴了一篇关于“双系统上重装Windows之后恢复ubuntu启动”的文章。今天该文的原创作者就在我的转贴上留了评论“终于碰到转帖留地址的了”，哈哈！其实这只是举手之劳。我很理解原创文章作者对自己文章的感情，所以即使我最初看到的是未标明原创作者的转贴，我也会google到该文章的原创出处标明出来。

不过这让我有了一个疑问：原创作者是怎么知道我转贴了他的文章的呢？

我又打开了这篇文章，随后发现奥秘所在：在该文的末尾处，有一段“Trackbacks and Pingbacks:”，其中将我的转贴列了出来：

这让我很好奇。我以前只知道trackback，并不知道pingback。随后google之，这里是wikipedia对pingback的解释：

A pingback is one of three types of linkbacks, methods for Web authors to request notification when somebody links to one of their documents. This enables authors to keep track of who is linking to, or referring to their articles. Some weblog software, such as Movable Type, Serendipity, WordPress and Telligent Community, support automatic pingbacks where all the links in a published article can be pinged when the article is published. A number of more advanced content management systems support pingbacks through the use of addons or extensions, including Drupal and Joomla.

Essentially, a pingback is an XML-RPC request (not to be confused with an ICMP ping) sent from Site A to Site B, when an author of the blog at Site A writes a post that links to Site B. However, it also requires a hyperlink. When Site B receives the notification signal, it automatically goes back to Site A checking for the existence of a live incoming link. If that link exists, the pingback is recorded successfully. This makes pingbacks less prone to spam than trackbacks. Pingback-enabled resources must either use an X-Pingback header or contain aelement to the XML-RPC script.

原来如此：WP会在发布文章的时候，检查该文章中的链接并发出pingback请求。随后我在WP的“设置->撰写->远程发布”里面看到“启用 WordPress、Movable Type、MetaWeblog 和 Blogger 的 XML-RPC 发布协议”这个选项，估计这个就是控制pingback到其他支持pingback网站(如http://www.aitilife.com/)的选项。

不过还有一个问题：我的转贴里面其实有两个链接分别指向了该网站的两篇文章，但是只有第一篇被成功pingback了，第二篇没有。这是否意味着在一篇文章里面有多个链接时，只有第一个将被pingback？