ostree

Ostree is a tool and core technology for managing bootable, versioned operating system trees. It stores the content of an OS as commits in a content-addressable repository. Each commit represents a complete snapshot of the filesystem at a point in time, and references a tree describing the exact layout and metadata such as parents and origins. Ostree is not a patch-based package manager; it builds and stores entire system states rather than applying in-place package updates.

The OSTree store contains objects such as blobs, trees, and commits, identified by cryptographic hashes. The design emphasizes content deduplication, offline operation, and efficient remote updates. Repositories can be synchronized between machines or networks, and updates are pulled as new commits rather than incremental file changes.

On a host, multiple deployments of the OS can coexist. The boot process selects a deployment to boot from, and the root filesystem is a checked-out copy of the selected commit. Upgrades create a new deployment pointing at a newer commit, and switching deployments is intended to be atomic. Rollbacks revert to a previous deployment by choosing an earlier commit at boot time.

OSTree is often used with a higher-level tool called rpm-ostree, which composes OS images by layering packages on top of base OSTree commits, and manages pulling updates from remote repositories. This approach underpins immutable OS distributions such as Fedora Silverblue and Fedora IoT, and supports custom deployments and streamlined, reliable upgrades. Ostree emphasizes reliability, atomic transitions, and the reuse of content across revisions, enabling simple rollbacks and predictable system state management.