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+# libostree
+{: .no_toc }
+
+1. TOC
+{:toc}
+
+This project is now known as "libostree", though it is still appropriate to use
+the previous name: "OSTree" (or "ostree"). The focus is on projects which use
+libostree's shared library, rather than users directly invoking the command line
+tools (except for build systems). However, in most of the rest of the
+documentation, we will use the term "OSTree", since it's slightly shorter, and
+changing all documentation at once is impractical. We expect to transition to
+the new name over time.
+
+As implied above, libostree is both a shared library and suite of command line
+tools that combines a "git-like" model for committing and downloading bootable
+filesystem trees, along with a layer for deploying them and managing the
+bootloader configuration.
+
+The core OSTree model is like git in that it checksums individual files and has
+a content-addressed-object store. It's unlike git in that it "checks out" the
+files via hardlinks, and they thus need to be immutable to prevent corruption.
+Therefore, another way to think of OSTree is that it's just a more polished
+version of
+[Linux VServer hardlinks](http://linux-vserver.org/index.php?title=util-vserver:Vhashify&oldid=2285).
+
+**Features:**
+
+ - Transactional upgrades and rollback for the system
+ - Replicating content incrementally over HTTP via GPG signatures and "pinned TLS" support
+ - Support for parallel installing more than just 2 bootable roots
+ - Binary history on the server side (and client)
+ - Introspectable shared library API for build and deployment systems
+ - Flexible support for multiple branches and repositories, supporting
+   projects like [flatpak](https://github.com/flatpak/flatpak) which
+   use libostree for applications, rather than hosts.
+
+## Operating systems and distributions using OSTree
+
+[Endless OS](https://endlessos.com/) uses libostree for their host system as
+well as flatpak. See
+their [eos-updater](https://github.com/endlessm/eos-updater)
+and [deb-ostree-builder](https://github.com/dbnicholson/deb-ostree-builder)
+projects.
+
+Fedora derivatives use rpm-ostree (noted below); there are 3 variants using OSTree:
+
+ - [Fedora CoreOS](https://getfedora.org/en/coreos/)
+ - [Fedora Silverblue](https://silverblue.fedoraproject.org/)
+ - [Fedora IoT](https://iot.fedoraproject.org/)
+
+Red Hat Enterprise Linux CoreOS is a derivative of Fedora CoreOS, used in [OpenShift 4](https://try.openshift.com/).
+The [machine-config-operator](https://github.com/openshift/machine-config-operator/blob/master/docs/OSUpgrades.md)
+manages upgrades.  RHEL CoreOS is also the successor to RHEL Atomic Host, which
+uses rpm-ostree as well.
+
+[GNOME Continuous](https://wiki.gnome.org/Projects/GnomeContinuous) is
+where OSTree was born - as a high performance continuous delivery/testing
+system for GNOME.
+
+[Liri OS](https://liri.io/download/silverblue/) has the option to install
+their distribution using ostree.
+
+## Distribution build tools
+
+[meta-updater](https://github.com/advancedtelematic/meta-updater) is
+a layer available for [OpenEmbedded](http://www.openembedded.org/wiki/Main_Page)
+systems.
+
+[QtOTA](http://doc.qt.io/QtOTA/) is Qt's over-the-air update framework
+which uses libostree.
+
+The [BuildStream](https://gitlab.com/BuildStream/buildstream) build and
+integration tool supports importing and exporting from libostree repos.
+
+Fedora [coreos-assembler](https://github.com/coreos/coreos-assembler) is
+the build tool used to generate Fedora CoreOS derivatives.
+
+## Projects linking to libostree
+
+[rpm-ostree](https://github.com/projectatomic/rpm-ostree) is used by the
+Fedora-derived operating systems listed above.  It is a full hybrid
+image/package system.  By default it uses libostree to atomically replicate a base OS
+(all dependency resolution is done on the server), but it supports "package layering", where
+additional RPMs can be layered on top of the base.  This brings a "best of both worlds""
+model for image and package systems.
+
+[eos-updater](https://github.com/endlessm/eos-updater) is a daemon that implements updates
+on EndlessOS.
+
+[flatpak](https://github.com/flatpak/flatpak) uses libostree for desktop
+application containers. Unlike most of the other systems here, flatpak does not
+use the "libostree host system" aspects (e.g. bootloader management), just the
+"git-like hardlink dedup". For example, flatpak supports a per-user OSTree
+repository.
+
+## Language bindings
+
+libostree is accessible via [GObject Introspection](https://gi.readthedocs.io/en/latest/);
+any language which has implemented the GI binding model should work.
+For example, Both [pygobject](https://pygobject.readthedocs.io/en/latest/)
+and [gjs](https://gitlab.gnome.org/GNOME/gjs) are known to work
+and further are actually used in libostree's test suite today.
+
+Some bindings take the approach of using GI as a lower level and
+write higher level manual bindings on top; this is more common
+for statically compiled languages.  Here's a list of such bindings:
+
+ - [ostree-go](https://github.com/ostreedev/ostree-go/)
+ - [ostree-rs](https://gitlab.com/fkrull/ostree-rs/)
+
+## Building
+
+Releases are available as GPG signed git tags, and most recent
+versions support extended validation using
+[git-evtag](https://github.com/cgwalters/git-evtag).
+
+However, in order to build from a git clone, you must update the
+submodules.  If you're packaging OSTree and want a tarball, I
+recommend using a "recursive git archive" script.  There are several
+available online;
+[this code](https://github.com/ostreedev/ostree/blob/master/packaging/Makefile.dist-packaging#L11)
+in OSTree is an example.
+
+Once you have a git clone or recursive archive, building is the
+same as almost every autotools project:
+
+```
+git submodule update --init
+env NOCONFIGURE=1 ./autogen.sh
+./configure --prefix=...
+make
+make install DESTDIR=/path/to/dest
+```
+
+## Contributing
+
+See [Contributing](docs/CONTRIBUTING.md).
+
+## Licensing
+
+The licensing for the *code* of libostree can be canonically found in the individual files;
+and the overall status in the [COPYING](https://github.com/ostreedev/ostree/blob/master/COPYING)
+file in the source.  Currently, that's LGPLv2+.  This also covers the man pages and API docs.
+
+The license for the manual documentation in the `doc/` directory is:
+`SPDX-License-Identifier: (CC-BY-SA-3.0 OR GFDL-1.3-or-later)`
+This is intended to allow use by Wikipedia and other projects.
+
+In general, files should have a `SPDX-License-Identifier` and that is canonical.