# 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
 ```