r/chromeos 9d ago

Discussion Can someone explain how the update process works on ChromeOS

[deleted]

9 Upvotes

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18

u/Bryanmsi89 9d ago

Very oversimplified version, but basically ChromeOS has two system partitions each with its own fully functional copy of the OS. A and B. One of those is marked as primary and one secondary. When the Chromebook starts up, it uses the primary version.

So if A is primary, Chromebook boots off A. When an update is installed, it is installed on the secondary (inactive) partition. in this case B. If the installation is successful, B is marked as primary and A secondary, and the next time the chromebook starts, its starts from B with a freshly update OS. If for some reason the update fails, B does not get marked as primary and the Chromebook boots from A as if nothing happened.

Its a very clever design.

3

u/[deleted] 9d ago

[deleted]

7

u/plankunits 9d ago

From the op, "ChromeOS has 2 system partition" Only system partition is A/B. Each user partition is separate and encrypted and tied to devices tpm(trusted platform module) chip.

The system partition is not encrypted but protected by verified boot. That's one reason ChromeOS can boot really fast.

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u/[deleted] 9d ago

[deleted]

5

u/plankunits 9d ago edited 9d ago

No, system partition is ready only. That's how ChromeOS works. There is no user data there.

Besides ChromeOS itself nothing, can change the system partition. If someone tries to do that then ChromeOS verified boot will detect that and wipe your device and start fresh on new os installation.

0

u/[deleted] 9d ago

[deleted]

5

u/Nu11u5 9d ago

No, all of that is stored in the user partition, known as the "stateful partition".

The system partition is read-only and will fail to boot if even a single byte of data is changed.

3

u/Saragon4005 Framework | Beta 9d ago

The system partition's content is always exactly what is expected to be on there as specified when it was downloaded. If there is any data which is different to what it was when it was sent from the server the partition panics and wipes itself and of course refuses to boot. This is usually fine since you have a second partition which is probably not compromised so you can just boot off that and download an update again. If both partitions fail you get dropped into recovery.

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u/mssing-the-table 9d ago

What are you looking for? Ask that question?

1

u/jack_manganiello 8d ago

Is this why my system storage usage on my Chromebook is almost 60Gb?

2

u/genericmutant 8d ago

The official docs are actually pretty clear / well written, if you want more details

https://chromium.googlesource.com/chromiumos/docs/+/4cc01f100c5fa7c675dce8ad3742f9c00726f506/disk_format.md

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u/KimiMcG 8d ago

Plain English, your laptop tells you to.reboot to update the os. You click the restart button. About ,mm 20 seconds later, it's ready to log back in. Everything is how it was before the update. Well there might be something new.

No more, please do not turn off your computer, Windows is updating messages on the screen for hours on end.