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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 But according to my (outdated?)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). –  HopelessN00b Mar 5 at 14:59

1 Answer 1

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. –  BlueCompute Mar 5 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. –  Nils Toedtmann Mar 5 at 14:24

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