OSTree is a tool for managing bootable, immutable, versioned filesystem trees.
During installation from the Photon OS ISO, you can select the Photon RPM-OSTree Server option to install Photon OS with the RPM-OSTree components and a minimal repository from which RPM-OSTree Hosts can be created.
On RPM-OSTree Server the repo is created at the following location:
/srv/rpm-ostree/repo
Here is the base configuration file that creates the repo:
/srv/rpm-ostree/photon-base.json
You can add or remove packages from the photon-base.json file and then run following commands to update the repo with a new commit:
cd /srv/rpm-ostree
rpm-ostree compose tree --repo=/srv/rpm-ostree/repo photon-base.json
The command above creates a new commit that contains your package-related changes.
OSTree host is an installation of Photon OS that retrieves the images from RPM-OSTree server during installation. It can get atomic updates from the same server during its lifecycle.
Host machines created from RPM-OSTree server can run the following commands to upgrade their host machine to the latest version from the RPM-OSTree server:
rpm-ostree upgrade
systemctl reboot