Question

I find the .Net FileSystemWatcher class really handy for writing utilities that automatically come to life when files show up in their watched folders. Is there any equivalent to this functionality in the *nix world that would allow me to watch a folder (and possibly all of its subdirectories)?

Edit: Preferably this will be something that doesn’t require kernel patches.

Answer 1

That would be Gamin the File Alteration Monitor or Inotify.

Edit: Mono does have Gamin bindings – in fact, its implementation of FileSystemWatcher uses Gamin. https://www.mono-project.com/docs/faq/technical/#what-are-the-issues-with-filesystemwatcher.

What are the issues with FileSystemWatcher?

The Mono implementation of FileSystemWatcher has a number of backends, the most optimal one, the one with fewer dependencies is the inotify-backend (available in Mono 1.1.17 and newer versions).

With this backend the kernel provides Mono with updates on any changes to files on the file system but it requires an inotify-enabled kernel, which only newer Linux distributions ship.

In older Linux systems, you must have installed FAM or Gamin (it will work with either one). You might need the -devel packets installed.

For the *BSD family, there’s a Kqueue based implementation that will be used when detected at runtime.

If none of the above work, Mono falls back to polling the directories for changes, which far from optimal.