How does a reboot work?

[Anonymous user]

With the help of apcupsd, the computer can safely be turned off. In this case, does it count as a power failure? I mean, the online documentation says that, by setting BIOS, you can reboot your computer when the power is back on. However, I can't agree that the aforementioned case is a candidate, since the computer itself would regard it as a normal shutdown. Then, how can I accomplish the reboot?

[BillP]

Hi,

The BIOS should have 3 states

ALWAYS ON: When power is cycled on, the computer will automatically turn on and boot up.

ALWAYS OFF: When power is cycled on, the computer will stay off until the user manually hits the On/Off soft switch.

LAST STATE: When power is cycled on, the computer will either come on or stay off depending on whether it was On or Off when the power was lost.

The computer if set to always on or last state should power back on automatically when AC is restored. If it does not you should contact the computer manufacture as the BIOS is the computer manufactures responsibility.   

[Anonymous user]

Suppose that BIOS was set to ALWAYS ON, and with the help of apcupsd the computer was safely turned off prior to the power loss.

1. If the state ALWAYS ON means that the computer must stay on at any time, the computer immediately boots as soon as it's powered off, and this cycle would continue until a total power loss, or
2. If the state ALWAYS ON means that the computer must be turned on only after a power loss, it won't boot up. This is because the computer was safely turned off, so it won't count as a power loss.

In either case, the expected behavior won't happen. Can you tell me what I'm missing here?

[BillP · Accepted solution]

Hi,

On 11/6/2018 6:44 AM, Il-seob said:

If the state ALWAYS ON means that the computer must stay on at any time, the computer immediately boots as soon as it's powered off, and this cycle would continue until a total power loss, or

No. Always on will only power cycle once AC has been cut. When the UPS switches to battery APCUPSD will command the OS down and can be configured to send a shutdown signal to the UPS. If the shutdown signal is not sent the UPS will remain running on battery until AC is restored or the battery drains. For the BIOS to restart the OS it must see AC cut. So if the UPS does not cut AC after APCUPSD tell the OS to power down it will remain down until a user intervenes.