Package systems versus image systems

Broadly speaking, software update systems for operating systems tend to fall cleanly into one of two camps: package-based or image-based.

Package system benefits and drawbacks



Image benefits and drawbacks



How rpm-ostree provides a middle ground

rpm-ostree in its default mode feels more like image replication, but the underlying architecture allows a lot of package-like flexibility.

In this default mode, packages are composed on a server, and clients can replicate that state reliably. For example, if one adds a package on the compose server, clients get it. If one removes a package, it's also removed when clients upgrade.

One simple mental model for rpm-ostree is: imagine taking a set of packages on the server side, install them to a chroot, then doing git commit on the result. And imagine clients just git pull -r from that. What OSTree adds to this picture is support for file uid/gid, extended attributes, handling of bootloader configuration, and merges of /etc.

To emphasize, replication is at a filesystem level - that means things like SELinux labels and uid/gid mappings are assigned on the server side.

On the other hand, rpm-ostree works on top of any Unix filesystem. It will not interfere with any filesystem or block-level snapshots or backups such as LVM or BTRFS.