git relink [--safe] <dir>… <master_dir>
This will scan 1 or more object repositories and look for objects in common with a master repository. Objects not already hardlinked to the master repository will be replaced with a hardlink to the master repository.
Stops if two objects with the same hash exist but have different sizes. Default is to warn and continue.
Directories containing a .git/objects/ subdirectory.
Part of the git(1) suite