I don't know whether this is a userland or kernel issue or a layer 8 problem.
After running a customized kernel, I found a server powered down. The culprit turned out to be dbcool->envsys->powerd fabulating some temperature rose above limits. envstat -d dbcool0 says: Current CritMax WarnMax WarnMin CritMin Unit [...] r2_temp: 53.250 54.000 45.000 degC [...] sysctl hw.dbcool0 says: [...] hw.dbcool0.r2_temp.Tmin = 44 hw.dbcool0.r2_temp.Ttherm = 57 hw.dbcool0.r2_temp.Thyst = 2 If I read that correctly, it means that at 54 degC, it's time for emergency shut-down, while only at 57 degC, fans have to run at full speed. (Also, it seems to be threatning the hardware if that temp falls below 45.) I have no clue where that magic value of 54 degC comes from. It's not in any config file I can find, I don't find such a value in sys/dev/i2c/dbcool.c. Is it the BIOS writing that value into the IC? Is it a chip manufacturer default? The board is a Tyan S2882-D, in case that matters. (Btw., does anyone know what r2_temp on that board is?) I turned off powerd for now. Thanks for any hints.