1. IDS filesystem baseline integrity checker. The fcheck utility is an IDS (Intrusion Detection System) which can be used to monitor changes to any given filesystem. Essentially, fcheck has the ability to monitor directories, files or complete filesystems for any additions, deletions, and modifications. It is configurable to exclude active log files, and can be ran as often as needed from the command line or cron making it extremely difficult to circumvent. From Debian 3.0r0 APT