For once I feel a little out of touch after I took a bit of a break from following the news to focus on studying, and suddenly everyone is talking about immutable distributions. What are they exactly? What are the benefits and the disadvantages of immutable systems?
Have you used Android? Has it ever failed an update or break due to an app install in a way that can’t be fixed by uninstalling it or factory resetting? Android is an immutable Linux OS. Its system files are stored on a read-only partition. They’re only mounted read-write during update. (That’s a lie, this is no longer the case, but it used to be, these days there are two partitions and the whole inactive partition is written during an update, or a volume snapshot pretending to be a partition is created and then merged, but functionally it’s consistent with the lie.) Apps are also stored in read-only form. One implication of this is that upon update, the partition/files you want to update are always in a predictable, unchanged state. That guarantees successful updates. It also allows trivial diff updates. The other implication of these facts is that you can always delete the mutable part of the OS, where your data and the apps’ data is stored, and you’ll always end up with a clean, working OS in a factory state. On Android you can also do this per-app by tapping “Clear data”.
Wouldn’t it be nice if you desktop or server behaved like this? Some folks think so and are trying to implement it.
There are few disadvantages beyond having to change how some systems work to accomodate this model. There’s typically more space wasted.
With tbis update system, I don’t understand why you can’t use your phone while doing it.
You can. Google pixel updates are just a reboot. Sadly many OEMs don’t do A/B updates, like samsung, so your phone can’t be used while updating the system partition
It’s worth mentioning that they often do this to reduce flash size, i.e. save 💰. Virtual AB was introduced to help with this but it’s relatively new. With it, there’s no need to reserve the space for 2x system partition. The needed extra space during update is taken from /data and released post success. There’s also a compressed virtual AB scheme now which helps reduce the space needed from /data to enable really space-crippled devices like CCwGTV and other Android TV things like Sony and other TVs.
