temperatures

Temperatures of a Linux, by SSH

Returns the temperature of each sensor the kernel exposes, and raises when a sensor crosses the thresholds it announces itself. A virtual machine has no sensor: the collector says so.

How it works

The collector reads with grep -s -H the files of /sys/class/hwmon: for each chip its name, and for each sensor its reading (temp*_input), its label, its high (max) and critical (crit) thresholds, in thousandths of a degree. Failing any sensor there, it reads the thermal zones of /sys/class/thermal (type and temperature), the only ones on some ARM boards.

• A sensor is named after its chip and its label (coretemp Package id 0), or its number when the driver gives no label (nvme temp1); two sensors of the same name each keep their own, the second carrying its chip.
• Thermal zones are not read beside hwmon: they often repeat its sensors.
• Portable: both trees are written by the kernel the same way on Alpine, Debian and Fedora; -s and -H are options of BusyBox as of GNU grep. Nothing is written on the target.

Prerequisites

• an SSH account for monitoring, without write rights;
• the fingerprint of the server's host key, set in protocol:ssh:fingerprint (not needed when the Security settings trust the first SSH fingerprint presented);
• the drivers of the sensors loaded (coretemp, k10temp, nct6775…): lm-sensors is not needed.

Outputs

Watches

Limits

• A machine without any sensor (a virtual machine, a container) stops the collector misconfigured.
• What is hot depends on the part: a laptop CPU at 90 °C is normal, a disk at 60 °C is not. The defaults of hot suit a server CPU; sensor-limit uses the part's own thresholds.
• A driver may announce no threshold, or a wrong one: sensor-limit then judges nothing, or too late.