This is a list of open-source search systems available on the web:

• Beagle is GNOME's full-text search system. It is based on the .NET framework and uses DotLucene (a .NET port of Lucene) as as the underlying indexing system. It receives file system change notifications through inotify.
  
  
• Lucene is an indexing system, implemented in Java. Lucene and its ports to other languages are used by many search systems, such as Nutch and Beagle.
  
  
• Nutch is an open-source web crawler and web search engine based on Lucene.
  
  
• Zettair is an information retrieval system developed by the search engine group at RMIT University.
  
  

The following webpages provide information about Linux file system change notification. File system notification is crucial to efficient real-time file system indexing, as it is the only way to immediately react to file changes.

• dnotify is the file change notification system of the Linux kernel. One of its main shortcomings is that an application needs to have one open file descriptor for every directory it is watching. Of course, this makes it impossible to watch the entire file system. It will probably be replaced by inotify in the not-too-distant future.
  
  
• The new dnotify notification service is similar to the existing dnotify kernel facilities, but allows recursive watches and additional events not supported by the original dnotify.
  
  
• fschange is a patch for the 2.6 Linux kernel that offers an event notification service for a broad range of file system events. By reading data from a proc file, an application can monitor the entire file system, being notified of mounts, umounts, file changes, file deletions, and many more events. The fschange homepage also gives some discussion of the pros and cons of the different approaches to Linux file system notification.
  
  
• The inotify repository on the kernel.org website. Inotify aims to become the successor of the Linux kernel's current notification system, dnotify. Edoceo provides a brief description of inotify and an example Perl program that shows how to use inotify.