Alert for Filesystem check does not work on CentOS 7

[Gergely Dudas]

Hi,

We would like to use monit's filesystem check on CentOS 7, but 
unfortunately it does not send any alert email.

Here is an example from monitrc what works on Ubuntu:

  check filesystem root_fs with path /
     if space usage > 80% for 1 times within 3 cycles then alert

What's wrong on CentOS 7?

monit-5.25.1-1.el7.x86_64
CentOS 7.5.1804

Thanks!

Regards,
Gergely Dudas