[Bug 1745463] Re: Disabling systemd-resolved breaks dhclient resolvconf integration

[Steve Langasek]

Nothing in your bug report explains why you have taken the initial step
to disable systemd-resolved on your system.  If it is simply that it is
"unwanted", that is insufficient justification for us to support a
configuration that involves disabling a component that the Ubuntu
development team has selected for inclusion in the core Ubuntu
experience.

The most likely resolution of this bug for 18.04 will be to remove the
resolvconf package from the Ubuntu archive, and force its removal from
systems on upgrade via Conflicts: from another relevant package (such as
systemd).

If there are specific inadequacies in the behavior of resolved when it
*is* enabled, please report these issues against the systemd package in
launchpad, so that they can be resolved for the benefit of all users of
Ubuntu 18.04.

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https://bugs.launchpad.net/bugs/1745463

Title:
  Disabling systemd-resolved breaks dhclient resolvconf integration

Status in resolvconf package in Ubuntu:
  New
Status in systemd package in Ubuntu:
  New

Bug description:
  To reproduce, mask resolved:
  sudo systemctl mask systemd-resolved.service

  ...then disable network-manager for ifupdown interfaces:
  $cat /etc/NetworkManager/NetworkManager.conf              
  [main]
  plugins=ifupdown,keyfile
  dns=default
  rc-manager=resolvconf

  [ifupdown]
  managed=false

  [device]
  wifi.scan-rand-mac-address=no

  ...and reboot.

  You'll note that resolvconf integration with dhclient is now broken.
  Interfaces listed in /etc/network/interfaces or
  /etc/network/interfaces.d/* will not provide DNS configuration in
  /etc/resolv.conf and /run/resolvconf/interfaces/.

  This is because /etc/dhcp/dhclient-enter-hooks.d/resolvconf defines
  "make_resolv_conf()" as a valid function for the BOUND case, but
  /etc/dhcp/dhclient-enter-hooks.d/resolved undefines it (who's nasty
  now, eh?) even though resolved is masked.

  The file existence check in the beginning of /etc/dhcp/dhclient-enter-
  hooks.d/resolved should be more thorough, i.e. it should ensure that
  resolved is enabled, rather than simply look for the existence of
  /lib/systemd/systemd-resolved. This works for me:

  -if [ -x /lib/systemd/systemd-resolved ] ; then
  +if [ -x /lib/systemd/systemd-resolved ] && systemctl -q is-enabled systemd-resolved ; then

  Arguably, /etc/dhcp/dhclient-enter-hooks.d/resolvconf should implement
  a similar check, looking for /run/resolvconf/enable-updates as a
  condition for meddling with DNS settings. If desired, I'll file a
  separate bug for that package.

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