That's so weird! There were little clues it used to work this way (well, test.sh really), but I didn't have context why it was changed. I haven't seen the exit behavior in my environment, which is Docker on Mac for Apple Silicon. I may have to do a bit of research. It's also worth exploring whether this was tied to a vsftpd version that has now automatically been superceded by Dependabot, which would be nice in terms of simple fixes (if true), but make it harder to confirm the original pathology. My best guess is that the problem is the "exec", and you might find a working approach that uses CMD but calls it as a subprocess in the entrypoint script, not as an in-place process replacement. That's my best explanation for why the patch you linked fixed the issue - it seemed really suspicious that hard coding the CMD would help, but calling vsftpd as a subprocess is a subtle difference that could actually affect child reaping semantics, and I think that's the part of the fix that really made the server work.