Overheating

The only incident in the game with a physical cause. A machine's cooling has failed, and no amount of software will talk the metal into cooling down.

What it does

On one machine, the temperature crosses the WARN threshold at 85 °C. At 95 °C it hits thermal shutdown: the machine goes DOWN and stays there for a full sixty seconds — the longest forced outage of any incident.

Temperature is clamped to a 40–120 °C band, so there is a real ceiling instead of a runaway to infinity. It does not need to run away; 95 °C is enough.

The log signature

The kernel logs that the temperature threshold was crossed and that the CPU is throttling; the hardware sensor may report that a fan has stopped:

05:14:03 web-03 kernel: nct6775 nct6775.656: fan1: alarm, input 0 RPM below min 600 RPM
05:18:30 web-03 kernel: CPU0: Core temperature above threshold, cpu clock throttled (total events = 312)
05:22:14 web-03 kernel: thermal thermal_zone0: critical temperature reached (105 C), shutting down

sensors shows temperatures and fan speeds, and journalctl -k shows kernel messages. Whether the fan line is there or not helps you tell whether the problem is hardware or load.

If you leave it alone

A guaranteed sixty-second outage on one machine, plus SLA debt if it stays open. On a small, early fleet, losing one of three web machines for a minute digs a serious hole in the shift average.

Heat is often a symptom

This is the incident most likely to be a consequence. Sustained load raises temperature, so a machine heating up during a flood may be reacting to the flood and not to a broken fan.

The way to tell: a real cooling failure is reported with a fan alarm and shows up on a single machine with no accompanying load story. Heat that follows saturation comes after the CPU is already pinned.

Two faces of intervention

Taking load off the heating machine can bring temporary relief; as long as the root cause stays in place, the temperature climbs again. You can read from the sensor output what a software intervention fixed and what it did not.

When it shows up