GIT_NAMESPACE=<namespace> git upload-pack GIT_NAMESPACE=<namespace> git receive-pack
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 git(1).
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 directory.
git-upload-pack(1) and 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 namespace.
The smart HTTP server, git-http-backend(1), will pass GIT_NAMESPACE through to the backend programs; see git-http-backend(1) for sample configuration to expose repository namespaces as repositories.
For a simple local test, you can use git-remote-ext(1):
git clone ext::'git --namespace=foo %s /tmp/prefixed.git'
The known attack vectors are as follows: