Refs

Like git, OSTree uses "refs" to which are text files that point to particular commits (i.e. filesystem trees). For example, the gnome-ostree operating system creates trees named like gnome-ostree/buildmaster/x86_64-runtime and gnome-ostree/buildmaster/x86_64-devel-debug. These two refs point to two different generated filesystem trees. In this example, the "runtime" tree contains just enough to run a basic GNOME system, and "devel-debug" contains all of the developer tools.

The ostree supports a simple syntax using the carat ^ to refer to the parent of a given commit. For example, gnome-ostree/buildmaster/x86_64-runtime^ refers to the previous build, and gnome-ostree/buildmaster/x86_64-runtime^^ refers to the one before that.