# What is OSTree and RPM-OSTree OSTree is a tool for managing bootable, immutable, versioned filesystem trees. ## Photon RPM-OSTree Server During installation from Photon ISO you can select "Photon RPM-OSTree Server" option that will install Photon with RPM-OSTree components and a minimal repo from which RPM-OSTree Hosts could be created. On RPM-OSTree Server the repo is created at following location. ``` /srv/rpm-ostree/repo ``` Following is the base configuration file used to create the repo. ``` /srv/rpm-ostree/photon-base.json ``` ### Updating RPM-OSTree repo image You can add/remove package from photon-base.json file and then run following command to update the repo with new commit. ``` cd /srv/rpm-ostree rpm-ostree compose tree --repo=/srv/rpm-ostree/repo photon-base.json ``` Above command will create a new commit that will have your package related changes in it. ## RPM-OSTree Host OSTree host is the installation of Photon that retrieves the images from RPM-OSTree server during installation. It can get atomic updates from the same server in its life time. ## Upgrading the Host installations Host machines created from RPM-OSTree server can run following commands to upgrade their Host machine to the latest version from RPM-OSTree server. ``` > rpm-ostree upgrade > systemctl reboot ```