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Nt1310 Unit 5

Decent Essays

Interactions with Install, Recovery, and Update After new software is installed by chromeos-install (including device recovery), or automatic update, a reboot is necessary for the new software to take effect. The first reboot after installing new software triggers special handling, depending on the specific installation use case. Rollback Protection After Update If a catastrophic system failure manifests immediately after an automatic update, Chrome OS Core can detect the failure and roll back to the previously installed software. The mechanism relies on a three-way interaction with the update_engine service, the firmware, and the system application. Each kernel GPT partition on the boot disk contains three special attributes flags, which the firmware uses to select which kernel to boot. The flags are designated “priority”, “successful”, and “tries”. The firmware selects the kernel based on these flags; the full rules are described in the design document for the …show more content…

In this state, the partition will be selected by the firmware as the first kernel to boot. On each boot, the firmware decrements the “tries” setting for the new kernel in the GPT. If “tries” is decremented to 0 and “successful” is never set to 1, the firmware will roll back to the previous working software. To prevent the rollback, the system must mark the kernel as good by setting the “tries” count to 0 and the “successful” flag to 1 sometime after booting. Chrome OS Core does not automatically mark the kernel good immediately after boot. Instead, when the update_engine service starts, it sets a 45 second timer. When the timer expires, update_engine invokes a script called chromeos-setgoodkernel. That script marks the kernel as good, after which rollback is no longer

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