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+gitnamespaces - Git namespaces
+Git supports dividing the refs of a single repository into multiple
+namespaces, each of which has its own branches, tags, and HEAD. Git can
+expose each namespace as an independent repository to pull from and push
+to, while sharing the object store, and exposing all the refs to
+operations such as linkgit:git-gc[1].
+Storing multiple repositories as namespaces of a single repository
+avoids storing duplicate copies of the same objects, such as when
+storing multiple branches of the same source. The alternates mechanism
+provides similar support for avoiding duplicates, but alternates do not
+prevent duplication between new objects added to the repositories
+without ongoing maintenance, while namespaces do.
+To specify a namespace, set the `GIT_NAMESPACE` environment variable to
+the namespace. For each ref namespace, git stores the corresponding
+refs in a directory under `refs/namespaces/`. For example,
+`GIT_NAMESPACE=foo` will store refs under `refs/namespaces/foo/`. You
+can also specify namespaces via the `--namespace` option to
+Note that namespaces which include a `/` will expand to a hierarchy of
+namespaces; for example, `GIT_NAMESPACE=foo/bar` will store refs under
+`refs/namespaces/foo/refs/namespaces/bar/`. This makes paths in
+`GIT_NAMESPACE` behave hierarchically, so that cloning with
+`GIT_NAMESPACE=foo/bar` produces the same result as cloning with
+`GIT_NAMESPACE=foo` and cloning from that repo with `GIT_NAMESPACE=bar`. It
+also avoids ambiguity with strange namespace paths such as `foo/refs/heads/`,
+which could otherwise generate directory/file conflicts within the `refs`
+linkgit:git-upload-pack[1] and linkgit:git-receive-pack[1] rewrite the
+names of refs as specified by `GIT_NAMESPACE`. git-upload-pack and
+git-receive-pack will ignore all references outside the specified
+The smart HTTP server, linkgit:git-http-backend[1], will pass
+GIT_NAMESPACE through to the backend programs; see
+linkgit:git-http-backend[1] for sample configuration to expose
+repository namespaces as repositories.
+For a simple local test, you can use linkgit:git-remote-ext[1]:
+git clone ext::'git --namespace=foo %s /tmp/prefixed.git'
+Anyone with access to any namespace within a repository can potentially
+access objects from any other namespace stored in the same repository.
+You can't directly say "give me object ABCD" if you don't have a ref to
+it, but you can do some other sneaky things like:
+. Claiming to push ABCD, at which point the server will optimize out the
+ need for you to actually send it. Now you have a ref to ABCD and can
+ fetch it (claiming not to have it, of course).
+. Requesting other refs, claiming that you have ABCD, at which point the
+ server may generate deltas against ABCD.
+None of this causes a problem if you only host public repositories, or
+if everyone who may read one namespace may also read everything in every
+other namespace (for instance, if everyone in an organization has read
+permission to every repository).