Today I would give my original Banana Pi (A20 / 1GB Ram) a new life/work and installed for testing armbian Bionic dev with kernel 4.17 (for not trashing my normal Pihole -  a OPi PC2 with armbian stretch)   After installing armbian bionic I did try to install Pihole via curl -sSL | bash but it "crashes" while starting dnsmaq - because it seems to collide with resolved at Port 53 see as reference :    After this reference I did edit /etc/systemd/resolved.conf and inserted DNSStubListener=no as a active line. (at the webpage above in some messages it says "DNSStubHandler=no" but doesnt work / isnt recognized)   After that restart resolvd:
sudo systemctl reload-or-restart systemd-resolved   and check that they doesnt collide anymore at port 53 and do start successfully:
sudo systemctl status dnsmasq.service systemd-resolved   After they do start successfully restart the Pihole-installation with: pihole -r and the installation will complete:
    At the end you could set a password for the WebUI with:
pihole -a -p