cannot install miniupnpd in a minimal ubuntu installation

[mai ling]

when you install a minimal impish, nft binary is not installed (iptables-nft is installed)

later on if you want to install miniupnpd, apt chooses miniupnpd-iptables which delivers /etc/miniupnpd/iptables_init.sh

the existence of this script and some other conditions are then checked by /usr/libexec/miniupnpd-startstop-helper.sh in ExecStartPre section of the systemd service, which fails when kernel filtering backend is nft but the userspace utilities are iptables-nft

later on when user learns from miniupnpd systemd service log that miniupnpd-nftables must be installed as well as the nftables package, miniupnpd-nftables cannot be installed because the apt utility attempts to autoconfigure miniupnpd too early, a step of reconfiguration is to start the service, which fails because installing miniupnpd-nftables only removes miniupnpd-iptables package but does not purge it, so /etc/miniupnpd/iptables_init.sh file remains on disk and misleads /usr/libexec/miniupnpd-startstop-helper.sh

the exit from this insane anti-user loop is to dpkg -P miniupnpd-iptables and reattempt installation of miniupnpd-nftables. or complete purge of miniupnpd and manually explicitly ask for miniupnpd-nftables and nftables packages when installing miniupnpd.

[mai ling (ml35)]

so to summarize:

apt install miniupnpnd DOES NOT WORK on a minimal impish setup and leaves user in an unfinished configuration of apt.