git gc: no space left on device, even though 3GB available and tmp_pack only 16MB

So here is what I found out so far: I couldn't find any documentation about these hidden '.tmp-XXXX-pack' in the .git/objects/pack folder. All other threads I can find are about non-hidden files with tmp_ prefix in the same folder. The hidden ones are also clearly created during the repack action and it's possible that these get stuck as well. I can't confirm whether that's still possible in git 2.3.0 (which I've updated to since), but at least the disk space requirement doesn't seem to have changed in this newer version - it still can't complete gc/repack. By deleting these .tmp-files I was able to recover my last 4GB and git still seems to behave fine afterwards - your results may vary though, so please make sure you have a backup before doing this. Finally, even 4GB wasn't enough to repack with gc --agressive. My .git folder is 1.1GB after the cleanup, my entire repository is 1.7GB. So 2x the size of your repository is possibly not enough for git gc, even with the aggressive option (which should save space). So I had to recover more space from elsewhere first.

Finally, here is what I have in my cleanup script now (which I think might be a good idea to call from a cron job):

#!/bin/bash
set -e

#git gc or remove tmp if that fails (because out of disk space)
git gc --aggressive --prune=now || rm -f .git/objects/*/tmp_* && rm -f .git/objects/*/.tmp-*

Similar scenario (about 2.3G available), except git gc itself would also fail with fatal: Unable to create '/home/ubuntu/my-app-here/.git/gc.pid.lock': No space left on device

What worked was to git prune first, and then run the gc.