Project Atomic, a Red Hat sponsored project, features an interesting new update system for RPM-based Linux operating systems called OSTree (rpm-ostree) which has been developed by Colin Walters over the last couple of years. Evidently OSTree supports atomic updates to an OS although I am not sure how that actually works because there is a lot of marketing hype and buzz words associated with Project Atomic including Docker containers.

In the default model, the RPMs are composed on a server into an OSTree repository, and client systems can replicate in an image-like fashion, including incremental updates. However, unlike traditional Linus distribution update mechanisms, it automatically keeps the previous version of the OS and makes it available for rollback.

The goal of Project Atomic is more than a new update mechanism:

Project Atomic integrates the tools and patterns of container-based application and service deployment with trusted operating system platforms to deliver an end-to-end hosting architecture that’s modern, reliable, and secure.

Upgrading a system is as easy as simply invoking rpm-ostree upgrade. The utility checks the repository URL specified in /ostree/repo/config to check for an updated OS codebase. If a new version is found, it is first downloaded and then deployed. At that point, a three-way merge of configuration is performed, using the new /etc as a base, and applying your specific changes on top. You then have to reboot your system for the update to take effect.

If you boot into the new tree and determine something is wrong, you can rollback to a previous tree (operating system snapshot) via a bootloader menu entry and invoke rpm-ostree rollback to permanently remove the OS update.

OSTree supports the storing of multiple trees and easily switching between any of the trees.

Interestingly, OSTree functionality and use cases kind of remind me of Live Update in Solaris 10.

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