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At some point recently, my fan stopped working. I've confirmed it's not the hardware, because in the bios I can start and stop the fan. This is an ubuntu 17.10 desktop host.

I noticed that lm-sensors wasn't noticing the fan. With a bit of searching, I found that adding the it87 module to /etc/modules caused lm-sensors to display temperature. (I'm not convinced I believe it for every probe it shows -- a few are negative -- but many of them look reasonable and move up and down with system load.)

As system load increases, I start seeing a bunch of processes like kidle_inject/0, which I understand are related to the kernel trying to slow down the CPU to avoid overheating (injecting idle cycles). And, indeed, with increased load I used to hear the fan come on. But no longer.

Any suggestions on what to look at?

jma
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This is what I've learned, which has solved my problem:

  • In the BIOS, I was able to confirm that the fan works and then change the threshold temperature a bit lower, which clearly gives me more breathing space.
  • Also in the BIOS, I noticed that the machine was set to hibernate rather than sleep. Since that has been known to cause problems on linux on other machines I've had, this seemed worth changing to something less drastic.

Between those two, the problem has disappeared. The fan no longer comes on slowly, then faster, but just all at once, then shuts off. But it doesn't spend much time running, so I'm ok with that.

I noticed whilst playing about that the bios seems to have updated itself, as evidenced by a different graphic at boot before grub takes over. I don't know how this happened, and, quite frankly, I find it more than slightly disturbing that it could do this without my approval. That said, I suspect the change happened with the new bios, wherever that came from.

jma
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