Created
November 15, 2018 05:37
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dnsmasq workaround to prevent systemd-resolved from overwriting my DNS
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| #!/bin/bash | |
| # place as your /etc/NetworkManager/dispatcher.d/dnsmasq and make executable | |
| INTERFACE=$1 | |
| ACTION=$2 | |
| DNSMASQ_RESOLVCONF=/run/dnsmasq/resolv.conf | |
| SYSTEMD_RESOLVCONF=/run/resolvconf/interface/systemd-resolved | |
| if [ "$ACTION" = "up" ]; then | |
| ( | |
| if [ "$DHCP4_DOMAIN_NAME" ]; then | |
| echo search $DHCP4_DOMAIN_NAME | |
| fi | |
| for ns in $IP4_NAMESERVERS $DHCP4_DOMAIN_NAME_SERVERS $IP6_NAMESERVERS $DHCP6_DOMAIN_NAME_SERVERS; do | |
| echo nameserver $ns | |
| done | |
| ) | tee $DNSMASQ_RESOLVCONF $SYSTEMD_RESOLVCONF >/dev/null | |
| fi |
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Under Ubuntu 18.04, if you want advanced local DNS behavior, you may opt to disable the default
systemd-resolvedand install/customize/enablednsmasq. However, naively doing so leads to a problem: dnsmasq WILL look for the systemd resolver, which, since you disabled it, it won't find, thus your system's Internet breaks. Manually editing your resolv.conf (either /etc/resolv.conf or /run/dnsmasq/resolv.conf) will not help as it will be overwritten on each restart / reconnection.This is because the default dnsmasq behavior is to look for DNS entries under
/run/resolvconf/interfaceand basically merge / create a resolv.conf file from there, which dnsmasq can then read. The problem, however, is that systemd installs a record there pointing to its own resolver,127.0.0.53, which remains there even ifsystemd-resolvedis off. In other words, every restart, network change, etc will cause resolvconf to overwrite your dnsmasq resolver entries with the systemd entry.This is not systemd's fault per se, but an inevitable consequence of having multiple local resolvers on your machine, as each one basically wants to tell "all other programs" to use IT as the resolver. This would be helped greatly if systemd removes the resolvconf entry when systemd-resolved itself is down (though I'm not sure what creates the resolvconf entry).
Above is my workaround to get advanced behavior using dnsmasq after disabling systemd-resolved. It is a network-manager dispatcher script that overwrites the systemd-resolved entry upon network start. I discovered this issue while disabling systemd-resolved as noted here (systemd/systemd#10779).