unbound: use ipv4 on older ubuntu

SpamHaus rejects queries from ipv6.
unbound does not work on ipv6 only servers without do-ip6: true
prefer-ip4 only works on ubuntu 24

this leads to a situation that we cannot support ipv6 only servers with
older ubuntu

setup/start.sh

@@ -94,10 +94,12 @@ systemctl restart systemd-journald
 usermod -a -G adm ${USER}
 
 log "Setting up unbound"
+rm -f /etc/unbound/unbound.conf.d/prefer-ip4.conf # old config file
 cp -f "${script_dir}/start/unbound/unbound.conf" /etc/unbound/unbound.conf.d/cloudron-network.conf
-unbound_version=$(unbound -V | sed -n 's/^Version \([0-9.]*\)/\1/p')
-if vergte "${unbound_version}" "1.19.2"; then
-    cp "${script_dir}/start/unbound/prefer-ip4.conf" /etc/unbound/unbound.conf.d/cloudron-prefer-ip4.conf
+if [[ "${ubuntu_version}" == "20.04" || "${ubuntu_version}" == "22.04" ]]; then
+    # on older ubuntu, prefer-ip4 option does not exist. do-ip6 has to be disabled because SpamHaus rejects IPv6 queries
+    # this means we cannot support IPv6 only servers on older ubuntu
+    sed -e 's/do-ip6: yes/do-ip6: no/' -e 's/prefer-ip4:/# prefer-ip4:/' -i /etc/unbound/unbound.conf.d/cloudron-network.conf
 fi
 rm -f /etc/unbound/unbound.conf.d/remote-control.conf # on ubuntu 24
 

setup/start/unbound/prefer-ip4.conf

@@ -1,6 +0,0 @@
-# Prefer IPv4 outbound queries. Spamhaus often rejects queries from IPv6 addresses
-# This setting is in a separate file since it only works from Ubuntu 24 , unbound 1.19.2
-
-server:
-    prefer-ip4: yes
-

setup/start/unbound/unbound.conf

@@ -6,11 +6,17 @@ server:
         interface: 127.0.0.150
         interface: 172.18.0.1
         ip-freebind: yes
-        do-ip6: yes
         access-control: 127.0.0.1 allow
         access-control: 172.18.0.1/16 allow
         cache-max-negative-ttl: 30
         cache-max-ttl: 300
+
+        # Prefer IPv4 outbound queries. Spamhaus often rejects queries from IPv6 addresses
+        # without this, unbound does not start on IPv6 only servers
+        do-ip6: yes
+        # this setting only works with ubuntu 24 and unbound >= 1.19.2
+        prefer-ip4: yes
+
         # enable below for logging to journalctl -u unbound
         # verbosity: 5
         # log-queries: yes