sudo apt-get install inotify-tools

inotify-wait /path/to/directory --recursive --monitor

-m, --monitor
   Instead of exiting  after  receiving  a  single  event,  execute
   indefinitely.   The default behaviour is to exit after the first
   event occurs.
-r, --recursive
   Watch all subdirectories of any directories passed as arguments.
   Watches will be set up recursively to an unlimited depth.   Sym‐
   bolic  links  are  not  traversed.  Newly created subdirectories
   will also be watched.