Control: reassign -1 passwd
I'm sorry for the delay. As far as Debian Unstable goes, I cannot
reproduce the issue on a clean VM, so it may be limited to Stretch as
you said. In any case, this part:
> root@debian:~# deluser foo
> Removing user `foo' ...
> Warning: group `foo' has no more members.
> userdel: user foo is currently used by process 4892
> /usr/sbin/deluser: `/usr/sbin/userdel foo' returned error code 8. Exiting.
shows that the error is coming from userdel. deluser issued the command
`/usr/bin/userdel foo` and userdel gave you this message. I'm therefore
reassigning this ticket to the passwd package, which is where userdel
comes from. You should hear from its maintainers as a result.
Afif Elghraoui | عفيف الغراوي