Read-Only File System: What is it?

[justsoup]

I have heard a lot of information about Ubuntu Touch's read-only filesystem, but I don't really understand how it works. Is it the same as an immutable distribution, and if so, how do updates actually work on a technical level?

Also, how is Ubuntu adapted to fit this read-only model?

[AppLee]

Hi @justsoup
The read only filesystem is just the result of a decision to create a stable system partition that the user is not suppose to modify.
It has several advantages, one them being that updates can be pushed as an image and incremental updates can be used.

Of course the user should have access to storage for installing apps, personal data and configuration files.
So basically what is considered the core of the system is on RO partitions and there is a user partition dedicated to user data.

Ubuntu as all Linux distros can accommodate for RO partitions, the limitation is that when a process requires to write something "permanently" (not in RAM) the file path should be configured into the user data partition.
This can be done using symlinks or custom paths and because it's all open source, it all can be done.

Also an operating system defines how the partitions and storage will be used, it also defines a way to install apps and the UI as well as default software and settings. Ubuntu Touch being intended primarily for phones and tablets, narrowing the possibilities was the option to give the user a product that just works. After installation, it just works as intended.
Of course the user can still choose to mess with the OS, but at their own risk.
Messing with the RO filesystem means that it may break the update system and force one to reinstall from scratch...

I hope it clarifies things a bit for you and don't mind some over simplifications

[justsoup]

@AppLee Thanks for the response! If I understand you the Ubuntu Touch OS is split between a system and userdata partition, with click apps modifying the userdata partition while system updates modify the system partition.

[AppLee]

@justsoup
Yes, I guess this is a good summary.