I have installed a fresh install of Check MK 2.0.0p4.
At a certain point i noticed that all my hosts got the service error: Check_MK (null).
When i set the “Criticality” of a folder to “Do not monitor this host” (The folder contains 11 Hosts)
Everything starts working again and the Check_MK services returns valid input.
This problem looks similar to
My issue is fixed, i had to many hosts with invalid snmp credentials.
For some reason if to many hosts fail their discovery all hosts in checkMK stop working.
I fixed the SNMP Credentials of 10 hosts and all other hosts started working.
If you have this issue: Check if your hosts are setup correctly.
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