As I mention every time I teach FOR577, I have been a big fan of file integrity monitoring tools (FIM) since Gene Kim first released Tripwire well over 30 years ago. I've used quite a few of them over the years including tripwire, OSSEC, samhain, and aide, just to name a few. For many years, I used the fcheck Perl script (by Michael A. Gumienny) that was available as an apt package on Ubuntu because it was lightning fast. Unfortunately, sometime between Ubuntu 16.04 and Ubuntu 20.04 (my memory fails me as to exactly when), it slowed down on many of the systems I managed to the point where instead of being able to run it 4-6 times a day, it would now sometimes take more than 24 hours to run. And that was just running it on select directories, not the entire system, the way I run tools like…