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Context: We rent unmanaged server hardware. The hoster's web dashboard offers a "automatic hardware reset" command (next to a "send ctrl-alt-del" command), but it fails to reboot the machine when the Linux kernel has panicked. The hoster's support insists that their "hardware reset" feature is "wired just like a Desktop PC's reset button" as opposed to a Desktop PC's power switch.

They also claim, that reset switches sometimes don't work in case of a frozen system. Is that correct?

I know that a mainboard's ATX power switch is only triggering a ACPI event that needs to be handled by the operating system. If that is frozen, nothing happens. But according to my (outdated?) memories, a mainboard's reset switch does not rely on the OS in any way, and restarts the computer, regardless on the state of the OS.

I have a feeling that this might be less a technical question, but a question about naming conventions. Maybe when the hoster says "like a PC's reset switch" they don't actually mean "wired to the mainboard's reset pins"?

Edit 1: i am talking about standard Intel x64 commodity hardware.

Edit 2: Maybe it's clearer if i split my issue up into three separate, smaller questions:

  1. What exactly happens when i short-cut the reset pins on a motherboard? ("It behaves as if power was cut" does not qualify as answer)
  2. Is it possible that short-cutting the reset pins on a motherboard does not lead to a reboot, e.g. in case of a completely frozen OS?
  3. What else could the my hoster mean with "... behaves exactly like the reset button of a Desktop PC", if not the reset pins on the motherboard?

PS: The hoster is Hetzner.de, their "Dedicated Root Server" line.

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  • They also claim, that reset switches sometimes don't work in case of a frozen system. Is that correct? Sounds like bullshit to me. I've never seen a hardware reset switch fail to kill power (rebooting the system). Mar 5, 2014 at 14:59

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AFAIK a reset button just shorts out 2 pins on the board to kill the power, then when it's reset it's like you've switched it off and on again. Effectively all it does.

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  • I agree, you can restart the power supply by shorting the black and green wires of the ATX power connector with a paperclip and that's essentially what the hard-reset switch does. The state of any OS should be immaterial. Mar 5, 2014 at 13:41
  • I know that the reset pins behave as if power was cut. But is the motherboard actually cutting its own power( or shortcutting ATX power connectors)? Sounds unlikely to me. Mar 5, 2014 at 14:24

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