Hardware Monitoring
Problem
When running Linux, especially older 6.x kernels, you might find that there are no thermal/power sensors available.
Solution
I tried several different options, but the only thing that worked was CoreFreq. It has its own kernel module, daemon and console client. The installation is pretty straightforward, just follow the official installation guide (note that there is a separate instruction for Proxmox). Don't forget to enable the daemon afterwards with systemctl enable corefreqd.
If you need to access some individual values to be used elsewhere, corefreq-cli supports JSON output. For example, here's how you can get current CPU temprature and power limit:
corefreq-cli -j | jq -c "{cputemp: ([.Cpu[].FlipFlop[].Thermal.Temp] | add/length | round ), cpupower: (.Proc.State.Power[0] | round)}"