Is there an async way of knowing a file has changed?

Question

I would like to asynchronously monitor a file for any changes. That is I would like to have a call back (possibly from kernel) in my program when the file has been modified/deleted. The file is just a plain text file. I know one can do this using a polling mechanism, but I am looking for an event based solution. I read about inotify, but looks like it needs patching of my kernel.

If the solution is POSIX compliant, its even better.

Answer 1

Inotify was merged to the Linux kernel way back in 2005, so unless you're in a very old system, you should be able to use it out of the box.

I don't think there exists a POSIX compliant solution for this. Mac OS X has FSEvents.

Also check the man page for inotify.

EDIT:

Don't know about your constraints and/or requirements, but there is also GFileMonitor if you use Glib (the C++ binding is glibmm) and QFileSystemWatcher is you use Qt. Those are probably more cross-platform friendly.

Answer 2

SGI's fam has been ported to several Unixes. There's also gamin.