LWN has had a number of articles on immutable distributions, such as Bluefin and Bazzite, in recent years. These distributions have taken a variety of approaches, including using rpm-ostree, filesystem snapshots, and bootable container (bootc) images. But those approaches, especially the latter, lead to extra complexity for a user attempting to install new software, instead of just using the existing package manager. AshOS (Any Snapshot Hierarchical OS) is an experimental AGPL-3-licensed “meta-distribution” that tried a different approach more in line with traditional package management. Although the project is no longer updated, it remains usable, and can still shed some light on a potential alternate path for users worried about adopting bootc-based approaches.

There are a few reasons to find immutable distributions appealing. The fact that updates can be applied and rolled back atomically is probably chief among them, but they also make it easier to reproduce a corresponding installation from a small set of configuration files. Immutability means that changes to the configuration are cleanly separated out, so it’s easy to see how a long-lived immutable system has been changed, and to reproduce a new system from those changes. The question, as always, is whether these benefits are worth the disk usage of A/B updates, build times of any custom images, complexity, and inconvenience. AshOS was an attempt to change the balance of that tradeoff by making it possible to add immutability onto an existing distribution, while keeping the existing distribution’s package manager in control.