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+# 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.

+

+### Changing the RPM repo

+Following is the rpm repo file being used for fetching RPMs by the rpm-ostree command to create the ostree repo. Change this file to point to different rpm repo than the default Photon repo.

+

+```

+/srv/rpm-ostree/photon-ostree.json

+```

+

+## RPM-OSTree Host

+

+OSTree host is the installation of Photon that retrives 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.

+

+```

+> ostree pull photon tp2/x86_64/minimal

+> rpm-ostree upgrade

+> systemctl reboot

+```