git version 2.19.1 steps to reproduce: # start in a brand new repo git init # create lots of unreachable loose objects for i in {1..10000}; do git commit-tree -m "$(head -c 12 /dev/urandom | base64)" "$(git mktree <&-)" <&-; done # this prints a lot of output and takes a minute or so to run # trigger git gc to run in the background git fetch # Auto packing the repository in background for optimum performance. # See "git help gc" for manual housekeeping. # trigger it again git fetch # Auto packing the repository in background for optimum performance. # See "git help gc" for manual housekeeping. # error: The last gc run reported the following. Please correct the root cause # and remove .git/gc.log. # Automatic cleanup will not be performed until the file is removed. # # warning: There are too many unreachable loose objects; run 'git prune' to remove them. # to manually fix this, run git prune: git prune # note that `git gc` does not fix the problem, and appears to do nothing in this situation: git gc According to the `git fetch` output, the `git help gc` docs, and the `git help prune` docs, I don't think I shouldn't ever have to run `git prune` manually, so this behavior seems like a bug to me. Please correct me if this is expected behavior. In case anyone's wondering why I'm creating unreachable loose objects, here's the usecase: https://stackoverflow.com/a/50403179/367916 . I would love a first-class solution to obviate that workaround, but that is probably a separate issue. Josh