Due to tons of variations of Linux environment recently introduced native file system watcher for Linux may refuse to function properly. First step in finding out a reason is to activate logging for it and see what's happening.
fsnotifier utilizes "user" facility of syslog(3) - messages usually can be found in /var/log/user.log. Verbosity is regulated via FSNOTIFIER_LOG_LEVEL environment variable, possible values are: debug, info, warning, error, off.
By default logging is switched off. To activate it set FSNOTIFIER_LOG_LEVEL to appropriate value before starting IDEA, e.g.:
Warning: "debug" verbosity level produces really huge amount of messages - use with care.