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Spørsmålet
SuperUser-leser FrozenKing vil vite hvordan datamaskinen vet når den har krasjet eller på annen måte hatt en feilaktig nedleggelse. Han skriver:
Actually, this question struck me because of power cuts in my house. When there is a power cut, there is a sudden loss of power from the computer.
How does the computer know that the shutdown was not properly done?
Det er et interessant spørsmål; klart moderne operativsystemer er godt klar over at noe har gått galt, men med hvilken mekanisme blir de oppmerksomme?
Svarene
SuperUser-bidragsyter David Schwartz tilbyr et generelt svar og innsikt i forskjellige operativsystemer:
For non-Windows based PCs, the detection is usually done on a per-filesystem basis. When a filesystem is mounted in read/write mode, an entry is written to the filesystem marking it dirty. When the filesystem is unmounted, an entry is written marking it clean. On startup, the operating system checks if its core filesystems are marked dirty, and if so it knows there wasn’t a clean shutdown - at least of those filesystems.
En annen bidragsyter, ChrisF svarer mer spesifikt til Windows-operativsystemet:
When powered off as normal, the bit is switched off. However, in case of power outage or improper (forced) shutdown, the bit will still be on the next time the PC is started.
This means that Windows can suggest remedial action – such as booting into Safe Mode.
In addition a Windows based PC will write an entry into event log detailing when and why (if known) it was shut down. It also writes an event when the PC starts up.
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