[Bug 1878955] Re: resolved dhclient-enter-hook complains about an empty file

[Dan Streetman]

bionic:

root at lp1878955-b:~# dpkg -l systemd|grep systemd
ii  systemd        237-3ubuntu10.43 amd64        system and service manager
root at lp1878955-b:~# dhclient -i ens8
cmp: EOF on /tmp/tmp.poVVjvvwPp which is empty


root at lp1878955-b:~# dpkg -l systemd|grep systemd
ii  systemd        237-3ubuntu10.44 amd64        system and service manager
root at lp1878955-b:~# dhclient -i ens8
root at lp1878955-b:~# 


** Tags removed: verification-needed verification-needed-bionic verification-needed-focal
** Tags added: verification-done verification-done-bionic verification-done-focal

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https://bugs.launchpad.net/bugs/1878955

Title:
  resolved dhclient-enter-hook complains about an empty file

Status in systemd package in Ubuntu:
  Fix Released
Status in systemd source package in Bionic:
  Fix Committed
Status in systemd source package in Focal:
  Fix Committed

Bug description:
  [impact]

  When starting/using `dhclient`, it will often return an error such as:

      cmp: EOF on /tmp/tmp.yCyV6zBzhB which is empty

  [test case]

  run dhclient for the first time (for the current boot) on a
  bionic/focal system, or remove the file(s) in
  /run/systemd/resolved.conf.d/ starting with 'isc-dhcp-*', and then run
  dhclient.

  [regression potential]

  any regression would likely cause the DNS configuration that dhclient
  gets to not be properly reported to systemd-resolved, resulting in
  problematic/broken systemd DNS resolution.

  [scope]

  this is needed in b/f

  this hook was removed from systemd starting in g, and the hook was not
  yet added in x, so this change is needed only in b and f.

  [original description]

  When starting/using `dhclient`, it will often return an error such as:

      cmp: EOF on /tmp/tmp.yCyV6zBzhB which is empty

  This is due to the use of `cmp` in "/etc/dhcp/dhclient-enter-
  hooks.d/resolved"

  Because the $oldstate file can be empty, or different, it should use
  `cmp --quiet`

  This happens when "/run/systemd/resolved.conf.d/isc-
  dhcp-v*-$interface.conf" files do not exist, or when the content
  changes.

  This is very loosely related to
  https://bugs.launchpad.net/ubuntu/+source/systemd/+bug/1805183

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