Verification for Groovy (246.6-1ubuntu1.5)

# Initial repro on groovy:

root@groovy:~# md5sum /etc/resolv.conf; stat -t -L /etc/resolv.conf 
6b21d96b644bdafc7a3094fe04ab4e88  /etc/resolv.conf
/etc/resolv.conf 729 8 81a4 102 104 8f 111 1 0 0 1625844827 1625844823 
1625844823 0 4096
root@groovy:~# ip link set eth0 down; sleep 1; ip link set eth0 up
root@groovy:~# md5sum /etc/resolv.conf; stat -t -L /etc/resolv.conf 
6b21d96b644bdafc7a3094fe04ab4e88  /etc/resolv.conf
/etc/resolv.conf 729 8 81a4 102 104 8f 111 1 0 0 1625844838 1625844837 
1625844837 0 4096

# Upgrading to -proposed

root@groovy:~# apt update && apt-get dist-upgrade -V
Get:1 http://security.ubuntu.com/ubuntu groovy-security InRelease [110 kB]
Hit:2 http://archive.ubuntu.com/ubuntu groovy InRelease 
Get:3 http://archive.ubuntu.com/ubuntu groovy-updates InRelease [115 kB]
Get:4 http://archive.ubuntu.com/ubuntu groovy-proposed InRelease [269 kB]
Get:5 http://archive.ubuntu.com/ubuntu groovy-updates/universe amd64 Packages 
[450 kB]
Get:6 http://archive.ubuntu.com/ubuntu groovy-proposed/restricted amd64 
Packages [100 kB]
Get:7 http://archive.ubuntu.com/ubuntu groovy-proposed/restricted 
Translation-en [14.7 kB]
Get:8 http://archive.ubuntu.com/ubuntu groovy-proposed/main amd64 Packages 
[83.6 kB]
Get:9 http://archive.ubuntu.com/ubuntu groovy-proposed/main Translation-en 
[22.3 kB]
Get:10 http://archive.ubuntu.com/ubuntu groovy-proposed/multiverse amd64 
Packages [11.6 kB]
Get:11 http://archive.ubuntu.com/ubuntu groovy-proposed/multiverse 
Translation-en [5,932 B]
Get:12 http://archive.ubuntu.com/ubuntu groovy-proposed/universe amd64 Packages 
[24.9 kB]
Get:13 http://archive.ubuntu.com/ubuntu groovy-proposed/universe Translation-en 
[12.8 kB]
Fetched 1,220 kB in 1s (840 kB/s)                                 
Reading package lists... Done
Building dependency tree       
Reading state information... Done
12 packages can be upgraded. Run 'apt list --upgradable' to see them.
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Calculating upgrade... Done
The following packages will be upgraded:
   libc-bin (2.32-0ubuntu3 => 2.32-0ubuntu3.2)
   libc6 (2.32-0ubuntu3 => 2.32-0ubuntu3.2)
   libgnutls30 (3.6.15-4ubuntu2 => 3.6.15-4ubuntu2.1)
   libnss-systemd (246.6-1ubuntu1.4 => 246.6-1ubuntu1.5)
   libpam-systemd (246.6-1ubuntu1.4 => 246.6-1ubuntu1.5)
   libsystemd0 (246.6-1ubuntu1.4 => 246.6-1ubuntu1.5)
   libudev1 (246.6-1ubuntu1.4 => 246.6-1ubuntu1.5)
   locales (2.32-0ubuntu3 => 2.32-0ubuntu3.2)
   systemd (246.6-1ubuntu1.4 => 246.6-1ubuntu1.5)
   systemd-sysv (246.6-1ubuntu1.4 => 246.6-1ubuntu1.5)
   systemd-timesyncd (246.6-1ubuntu1.4 => 246.6-1ubuntu1.5)
   udev (246.6-1ubuntu1.4 => 246.6-1ubuntu1.5)
12 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
Need to get 14.1 MB of archives.
After this operation, 3,072 B of additional disk space will be used.
Do you want to continue? [Y/n] 
Get:1 http://archive.ubuntu.com/ubuntu groovy-proposed/main amd64 libc6 amd64 
2.32-0ubuntu3.2 [2,680 kB]
Get:2 http://archive.ubuntu.com/ubuntu groovy-proposed/main amd64 libc-bin 
amd64 2.32-0ubuntu3.2 [628 kB]
Get:3 http://archive.ubuntu.com/ubuntu groovy-proposed/main amd64 
libnss-systemd amd64 246.6-1ubuntu1.5 [94.6 kB]
Get:4 http://archive.ubuntu.com/ubuntu groovy-proposed/main amd64 udev amd64 
246.6-1ubuntu1.5 [1,340 kB]
Get:5 http://archive.ubuntu.com/ubuntu groovy-proposed/main amd64 libudev1 
amd64 246.6-1ubuntu1.5 [69.2 kB]
Get:6 http://archive.ubuntu.com/ubuntu groovy-proposed/main amd64 systemd-sysv 
amd64 246.6-1ubuntu1.5 [10.3 kB]
Get:7 http://archive.ubuntu.com/ubuntu groovy-proposed/main amd64 
systemd-timesyncd amd64 246.6-1ubuntu1.5 [28.2 kB]
Get:8 http://archive.ubuntu.com/ubuntu groovy-proposed/main amd64 
libpam-systemd amd64 246.6-1ubuntu1.5 [179 kB]
Get:9 http://archive.ubuntu.com/ubuntu groovy-proposed/main amd64 libgnutls30 
amd64 3.6.15-4ubuntu2.1 [770 kB]
Get:10 http://archive.ubuntu.com/ubuntu groovy-proposed/main amd64 systemd 
amd64 246.6-1ubuntu1.5 [4,166 kB]
Get:11 http://archive.ubuntu.com/ubuntu groovy-proposed/main amd64 libsystemd0 
amd64 246.6-1ubuntu1.5 [274 kB]
Get:12 http://archive.ubuntu.com/ubuntu groovy-proposed/main amd64 locales all 
2.32-0ubuntu3.2 [3,879 kB]
Fetched 14.1 MB in 4s (3,313 kB/s)    
Preconfiguring packages ...
(Reading database ... 14742 files and directories currently installed.)
Preparing to unpack .../libc6_2.32-0ubuntu3.2_amd64.deb ...
Unpacking libc6:amd64 (2.32-0ubuntu3.2) over (2.32-0ubuntu3) ...
Setting up libc6:amd64 (2.32-0ubuntu3.2) ...
(Reading database ... 14742 files and directories currently installed.)
Preparing to unpack .../libc-bin_2.32-0ubuntu3.2_amd64.deb ...
Unpacking libc-bin (2.32-0ubuntu3.2) over (2.32-0ubuntu3) ...
Setting up libc-bin (2.32-0ubuntu3.2) ...
(Reading database ... 14742 files and directories currently installed.)
Preparing to unpack .../libnss-systemd_246.6-1ubuntu1.5_amd64.deb ...
Unpacking libnss-systemd:amd64 (246.6-1ubuntu1.5) over (246.6-1ubuntu1.4) ...
Preparing to unpack .../udev_246.6-1ubuntu1.5_amd64.deb ...
Unpacking udev (246.6-1ubuntu1.5) over (246.6-1ubuntu1.4) ...
Preparing to unpack .../libudev1_246.6-1ubuntu1.5_amd64.deb ...
Unpacking libudev1:amd64 (246.6-1ubuntu1.5) over (246.6-1ubuntu1.4) ...
Setting up libudev1:amd64 (246.6-1ubuntu1.5) ...
(Reading database ... 14742 files and directories currently installed.)
Preparing to unpack .../systemd-sysv_246.6-1ubuntu1.5_amd64.deb ...
Unpacking systemd-sysv (246.6-1ubuntu1.5) over (246.6-1ubuntu1.4) ...
Preparing to unpack .../systemd-timesyncd_246.6-1ubuntu1.5_amd64.deb ...
Unpacking systemd-timesyncd (246.6-1ubuntu1.5) over (246.6-1ubuntu1.4) ...
Preparing to unpack .../libpam-systemd_246.6-1ubuntu1.5_amd64.deb ...
Unpacking libpam-systemd:amd64 (246.6-1ubuntu1.5) over (246.6-1ubuntu1.4) ...
Preparing to unpack .../libgnutls30_3.6.15-4ubuntu2.1_amd64.deb ...
Unpacking libgnutls30:amd64 (3.6.15-4ubuntu2.1) over (3.6.15-4ubuntu2) ...
Setting up libgnutls30:amd64 (3.6.15-4ubuntu2.1) ...
(Reading database ... 14742 files and directories currently installed.)
Preparing to unpack .../systemd_246.6-1ubuntu1.5_amd64.deb ...
Unpacking systemd (246.6-1ubuntu1.5) over (246.6-1ubuntu1.4) ...
Preparing to unpack .../libsystemd0_246.6-1ubuntu1.5_amd64.deb ...
Unpacking libsystemd0:amd64 (246.6-1ubuntu1.5) over (246.6-1ubuntu1.4) ...
Setting up libsystemd0:amd64 (246.6-1ubuntu1.5) ...
(Reading database ... 14743 files and directories currently installed.)
Preparing to unpack .../locales_2.32-0ubuntu3.2_all.deb ...
Unpacking locales (2.32-0ubuntu3.2) over (2.32-0ubuntu3) ...
Setting up locales (2.32-0ubuntu3.2) ...
Generating locales (this might take a while)...
  en_AG.UTF-8... done
  en_AU.UTF-8... done
  en_BW.UTF-8... done
  en_CA.UTF-8... done
  en_DK.UTF-8... done
  en_GB.UTF-8... done
  en_HK.UTF-8... done
  en_IE.UTF-8... done
  en_IL.UTF-8... done
  en_IN.UTF-8... done
  en_NG.UTF-8... done
  en_NZ.UTF-8... done
  en_PH.UTF-8... done
  en_SG.UTF-8... done
  en_US.UTF-8... done
  en_ZA.UTF-8... done
  en_ZM.UTF-8... done
  en_ZW.UTF-8... done
Generation complete.
Setting up udev (246.6-1ubuntu1.5) ...
Setting up systemd (246.6-1ubuntu1.5) ...
Setting up systemd-timesyncd (246.6-1ubuntu1.5) ...
Setting up systemd-sysv (246.6-1ubuntu1.5) ...
Setting up libnss-systemd:amd64 (246.6-1ubuntu1.5) ...
Setting up libpam-systemd:amd64 (246.6-1ubuntu1.5) ...
Processing triggers for libc-bin (2.32-0ubuntu3.2) ...
Processing triggers for dbus (1.12.20-1ubuntu1) ...

# Config the fix worked:

root@groovy:~# md5sum /etc/resolv.conf; stat -t -L /etc/resolv.conf 
6b21d96b644bdafc7a3094fe04ab4e88  /etc/resolv.conf
/etc/resolv.conf 729 8 81a4 102 104 8f 124 1 0 0 1625844950 1625844924 
1625844924 0 4096
root@groovy:~# ip link set eth0 down; sleep 1; ip link set eth0 up
root@groovy:~# md5sum /etc/resolv.conf; stat -t -L /etc/resolv.conf 
6b21d96b644bdafc7a3094fe04ab4e88  /etc/resolv.conf
/etc/resolv.conf 729 8 81a4 102 104 8f 124 1 0 0 1625844955 1625844924 
1625844924 0 4096

Verification for Hirsute (247.3-3ubuntu3.2)


# Initial repro on hirsute:

root@hirsute:~# md5sum /etc/resolv.conf; stat -t -L /etc/resolv.conf 
1cd09c0cc2c017d30c3bdec6325176b1  /etc/resolv.conf
/etc/resolv.conf 738 8 81a4 101 103 83 131 1 0 0 1625844576 1625844570 
1625844570 0 4096
root@hirsute:~# ip link set eth0 down; sleep 1; ip link set eth0 up
root@hirsute:~# md5sum /etc/resolv.conf; stat -t -L /etc/resolv.conf 
1cd09c0cc2c017d30c3bdec6325176b1  /etc/resolv.conf
/etc/resolv.conf 738 8 81a4 101 103 83 131 1 0 0 1625844592 1625844591 
1625844591 0 4096

# Upgrading to -proposed

root@hirsute:~# apt update && apt-get dist-upgrade -V
Get:1 http://security.ubuntu.com/ubuntu hirsute-security InRelease [101 kB]
Hit:2 http://archive.ubuntu.com/ubuntu hirsute InRelease
Get:3 http://archive.ubuntu.com/ubuntu hirsute-updates InRelease [109 kB]
Get:4 http://archive.ubuntu.com/ubuntu hirsute-proposed InRelease [269 kB]
Get:5 http://archive.ubuntu.com/ubuntu hirsute-updates/main amd64 Packages [262 
kB]
Get:6 http://archive.ubuntu.com/ubuntu hirsute-updates/universe amd64 Packages 
[255 kB]
Get:7 http://archive.ubuntu.com/ubuntu hirsute-proposed/restricted amd64 
Packages [96.5 kB]
Get:8 http://archive.ubuntu.com/ubuntu hirsute-proposed/restricted 
Translation-en [13.9 kB]
Get:9 http://archive.ubuntu.com/ubuntu hirsute-proposed/main amd64 Packages 
[91.8 kB]
Get:10 http://archive.ubuntu.com/ubuntu hirsute-proposed/main Translation-en 
[25.5 kB]
Get:11 http://archive.ubuntu.com/ubuntu hirsute-proposed/multiverse amd64 
Packages [5,344 B]
Get:12 http://archive.ubuntu.com/ubuntu hirsute-proposed/multiverse 
Translation-en [4,720 B]
Get:13 http://archive.ubuntu.com/ubuntu hirsute-proposed/universe amd64 
Packages [31.3 kB]
Get:14 http://archive.ubuntu.com/ubuntu hirsute-proposed/universe 
Translation-en [16.2 kB]
Fetched 1,281 kB in 1s (918 kB/s)                                 
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
11 packages can be upgraded. Run 'apt list --upgradable' to see them.
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
Calculating upgrade... Done
The following packages will be upgraded:
   libapparmor1 (3.0.0-0ubuntu7 => 3.0.0-0ubuntu7.1)
   libnss-systemd (247.3-3ubuntu3.1 => 247.3-3ubuntu3.2)
   libpam-systemd (247.3-3ubuntu3.1 => 247.3-3ubuntu3.2)
   libssl1.1 (1.1.1j-1ubuntu3 => 1.1.1j-1ubuntu3.1)
   libsystemd0 (247.3-3ubuntu3.1 => 247.3-3ubuntu3.2)
   libudev1 (247.3-3ubuntu3.1 => 247.3-3ubuntu3.2)
   openssl (1.1.1j-1ubuntu3 => 1.1.1j-1ubuntu3.1)
   systemd (247.3-3ubuntu3.1 => 247.3-3ubuntu3.2)
   systemd-sysv (247.3-3ubuntu3.1 => 247.3-3ubuntu3.2)
   systemd-timesyncd (247.3-3ubuntu3.1 => 247.3-3ubuntu3.2)
   udev (247.3-3ubuntu3.1 => 247.3-3ubuntu3.2)
11 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
Need to get 8,337 kB of archives.
After this operation, 3,072 B of additional disk space will be used.
Do you want to continue? [Y/n] 
Get:1 http://archive.ubuntu.com/ubuntu hirsute-proposed/main amd64 
libnss-systemd amd64 247.3-3ubuntu3.2 [96.0 kB]
Get:2 http://archive.ubuntu.com/ubuntu hirsute-proposed/main amd64 libsystemd0 
amd64 247.3-3ubuntu3.2 [277 kB]
Get:3 http://archive.ubuntu.com/ubuntu hirsute-proposed/main amd64 
systemd-timesyncd amd64 247.3-3ubuntu3.2 [28.1 kB]
Get:4 http://archive.ubuntu.com/ubuntu hirsute-proposed/main amd64 systemd-sysv 
amd64 247.3-3ubuntu3.2 [10.3 kB]
Get:5 http://archive.ubuntu.com/ubuntu hirsute-proposed/main amd64 
libpam-systemd amd64 247.3-3ubuntu3.2 [181 kB]
Get:6 http://archive.ubuntu.com/ubuntu hirsute-proposed/main amd64 systemd 
amd64 247.3-3ubuntu3.2 [4,326 kB]
Get:7 http://archive.ubuntu.com/ubuntu hirsute-proposed/main amd64 udev amd64 
247.3-3ubuntu3.2 [1,366 kB]
Get:8 http://archive.ubuntu.com/ubuntu hirsute-proposed/main amd64 libudev1 
amd64 247.3-3ubuntu3.2 [70.3 kB]
Get:9 http://archive.ubuntu.com/ubuntu hirsute-proposed/main amd64 libapparmor1 
amd64 3.0.0-0ubuntu7.1 [34.5 kB]
Get:10 http://archive.ubuntu.com/ubuntu hirsute-proposed/main amd64 libssl1.1 
amd64 1.1.1j-1ubuntu3.1 [1,324 kB]
Get:11 http://archive.ubuntu.com/ubuntu hirsute-proposed/main amd64 openssl 
amd64 1.1.1j-1ubuntu3.1 [624 kB]
Fetched 8,337 kB in 3s (2,726 kB/s)
Preconfiguring packages ...
(Reading database ... 14885 files and directories currently installed.)
Preparing to unpack .../libnss-systemd_247.3-3ubuntu3.2_amd64.deb ...
Unpacking libnss-systemd:amd64 (247.3-3ubuntu3.2) over (247.3-3ubuntu3.1) ...
Preparing to unpack .../libsystemd0_247.3-3ubuntu3.2_amd64.deb ...
Unpacking libsystemd0:amd64 (247.3-3ubuntu3.2) over (247.3-3ubuntu3.1) ...
Setting up libsystemd0:amd64 (247.3-3ubuntu3.2) ...
(Reading database ... 14885 files and directories currently installed.)
Preparing to unpack .../0-systemd-timesyncd_247.3-3ubuntu3.2_amd64.deb ...
Unpacking systemd-timesyncd (247.3-3ubuntu3.2) over (247.3-3ubuntu3.1) ...
Preparing to unpack .../1-systemd-sysv_247.3-3ubuntu3.2_amd64.deb ...
Unpacking systemd-sysv (247.3-3ubuntu3.2) over (247.3-3ubuntu3.1) ...
Preparing to unpack .../2-libpam-systemd_247.3-3ubuntu3.2_amd64.deb ...
Unpacking libpam-systemd:amd64 (247.3-3ubuntu3.2) over (247.3-3ubuntu3.1) ...
Preparing to unpack .../3-systemd_247.3-3ubuntu3.2_amd64.deb ...
Unpacking systemd (247.3-3ubuntu3.2) over (247.3-3ubuntu3.1) ...
Preparing to unpack .../4-udev_247.3-3ubuntu3.2_amd64.deb ...
Unpacking udev (247.3-3ubuntu3.2) over (247.3-3ubuntu3.1) ...
Preparing to unpack .../5-libudev1_247.3-3ubuntu3.2_amd64.deb ...
Unpacking libudev1:amd64 (247.3-3ubuntu3.2) over (247.3-3ubuntu3.1) ...
Setting up libudev1:amd64 (247.3-3ubuntu3.2) ...
(Reading database ... 14886 files and directories currently installed.)
Preparing to unpack .../libapparmor1_3.0.0-0ubuntu7.1_amd64.deb ...
Unpacking libapparmor1:amd64 (3.0.0-0ubuntu7.1) over (3.0.0-0ubuntu7) ...
Preparing to unpack .../libssl1.1_1.1.1j-1ubuntu3.1_amd64.deb ...
Unpacking libssl1.1:amd64 (1.1.1j-1ubuntu3.1) over (1.1.1j-1ubuntu3) ...
Setting up libssl1.1:amd64 (1.1.1j-1ubuntu3.1) ...
(Reading database ... 14886 files and directories currently installed.)
Preparing to unpack .../openssl_1.1.1j-1ubuntu3.1_amd64.deb ...
Unpacking openssl (1.1.1j-1ubuntu3.1) over (1.1.1j-1ubuntu3) ...
Setting up libapparmor1:amd64 (3.0.0-0ubuntu7.1) ...
Setting up udev (247.3-3ubuntu3.2) ...
Setting up openssl (1.1.1j-1ubuntu3.1) ...
Setting up systemd (247.3-3ubuntu3.2) ...
Setting up systemd-timesyncd (247.3-3ubuntu3.2) ...
Setting up systemd-sysv (247.3-3ubuntu3.2) ...
Setting up libnss-systemd:amd64 (247.3-3ubuntu3.2) ...
Setting up libpam-systemd:amd64 (247.3-3ubuntu3.2) ...
Processing triggers for libc-bin (2.33-0ubuntu5) ...
Processing triggers for dbus (1.12.20-1ubuntu3) ...

# Config the fix worked:

root@hirsute:~# md5sum /etc/resolv.conf; stat -t -L /etc/resolv.conf 
1cd09c0cc2c017d30c3bdec6325176b1  /etc/resolv.conf
/etc/resolv.conf 738 8 81a4 101 103 83 84 1 0 0 1625844724 1625844700 
1625844700 0 4096
root@hirsute:~# ip link set eth0 down; sleep 1; ip link set eth0 up
root@hirsute:~# md5sum /etc/resolv.conf; stat -t -L /etc/resolv.conf 
1cd09c0cc2c017d30c3bdec6325176b1  /etc/resolv.conf
/etc/resolv.conf 738 8 81a4 101 103 83 84 1 0 0 1625844732 1625844700 
1625844700 0 4096

** Tags removed: verification-needed verification-needed-groovy 
verification-needed-hirsute
** Tags added: verification-done verification-done-groovy 
verification-done-hirsute

-- 
You received this bug notification because you are a member of Ubuntu
Touch seeded packages, which is subscribed to systemd in Ubuntu.
https://bugs.launchpad.net/bugs/1891215

Title:
  systemd-resolved re-creates /run/systemd/resolve/*resolv.conf for
  every IPv6 RA received

Status in systemd:
  Unknown
Status in systemd package in Ubuntu:
  Fix Released
Status in systemd source package in Bionic:
  New
Status in systemd source package in Focal:
  Fix Committed
Status in systemd source package in Groovy:
  Fix Committed
Status in systemd source package in Hirsute:
  Fix Committed

Bug description:
  [impact]

  networking changes, like RA events, can cause systemd-resolved to re-
  write the resolv.conf file, even if the contents didn't change,
  resulting in unnecessary increased amount of inotify events

  [test case]

  see original description for ipv6ra-related reproducer, or simple
  reproducer here:

  configure networkd with some config for (e.g.) eth0, but not a config
  that would result in /etc/resolv.conf changing when the interface goes
  up/down - for example, use static config with no DNS search domains.
  Then bring eth0 up/down while observing the md5sum (file content) does
  not change but the mtime does change.

  root@lp1891215-h:~# ip l set down dev eth0
  root@lp1891215-h:~# md5sum /etc/resolv.conf
  db23e80078515192c312e5f321ff0340  /etc/resolv.conf
  root@lp1891215-h:~# stat -t -L /etc/resolv.conf
  /etc/resolv.conf 740 8 81a4 101 103 fc 188 1 0 0 1625238218 1625238216 
1625238216 0 4096
  root@lp1891215-h:~# ip l set up dev eth0
  root@lp1891215-h:~# md5sum /etc/resolv.conf
  db23e80078515192c312e5f321ff0340  /etc/resolv.conf
  root@lp1891215-h:~# stat -t -L /etc/resolv.conf
  /etc/resolv.conf 740 8 81a4 101 103 fc 188 1 0 0 1625238227 1625238226 
1625238226 0 4096

  [regression potential]

  regressions would result in incorrect or missing data in the
  resolv.conf file, possibly resulting in dns failures or errors

  [scope]

  this is needed for h and eralier

  this is (potentially) fixed upstream by
  f3e1f00d03445911ee73729219cea88c8a70c612 which in first included in
  v248, so this is needed in hirsute and earlier

  [original description]

  # Issue description:

  On 2 Linode VMs that are used as lxd hosts, we noticed that
  /run/systemd/resolve/*resolv.conf were re-created quite frequently (~
  once per second). We noticed because of the log noise from lxd's
  dnsmasq instance using inotify to watch the target of /etc/resolv.conf
  (which points to the stub-resolv.conf in our case). This was (wrongly)
  reported as a lxd bug (https://github.com/lxc/lxd/issues/7765) until
  it became apparent it was more likely to be a problem with
  systemd(-resolved)?.

  The log noise is the observable problem that would be nice to see
  addressed:

    root@lxd02:~# uptime
     17:55:48 up  9:52,  1 user,  load average: 0.18, 0.11, 0.05
    root@lxd02:~# journalctl -b0 | grep -cF dnsmasq
    158609

  Upon further investigation, it seems that systemd-resolved re-creates
  the resolv.conf and stub-resolv.conf files whenever an IPv6 RA is
  received.

  1) One can observe that by setting systemd-resolved's service in debug
  mode:

  $ sudo systemctl edit systemd-resolved

  and in the editor that is opened, add and save this content:

  [Service]
  Environment=SYSTEMD_LOG_LEVEL=debug

  then restart systemd-resolved and watch the logs scroll by with:

  $ journalctl -fu systemd-resolved

  3) In another terminal, watch the files be recreated with:

  watch -d -n 0.1 stat /run/systemd/resolve/stub-resolv.conf

  3) In yet another terminal, run a packet capture and watch "ICMP6,
  router advertisement" messages come by:

  sudo tcpdump -ni eth0 icmp6

  You will see that every time a RA packet comes in, resolved's journal
  will log this:

    Aug 11 17:33:55 lxd02 systemd-resolved[15368]: Sent message
  type=signal sender=n/a destination=n/a path=/org/freedesktop/resolve1
  interface=org.freedesktop.DBus.Properties member=PropertiesChanged
  cookie=244 reply_cookie=0 signature=sa{sv}as error-name=n/a error-
  message=n/a

  And the stat monitoring terminal will blink to highlight the new inode
  and timestamps of the freshly replaced stub-resolv.conf file.

  # Additional information:

  root@lxd02:~# lsb_release -rd
  Description:  Ubuntu 20.04.1 LTS
  Release:      20.04

  root@lxd02:~# apt-cache policy systemd
  systemd:
    Installed: 245.4-4ubuntu3.2
    Candidate: 245.4-4ubuntu3.2
    Version table:
   *** 245.4-4ubuntu3.2 500
          500 http://archive.ubuntu.com/ubuntu focal-updates/main amd64 Packages
          100 /var/lib/dpkg/status
       245.4-4ubuntu3 500
          500 http://archive.ubuntu.com/ubuntu focal/main amd64 Packages

  root@lxd02:~# uname -a
  Linux lxd01 5.4.0-42-generic #46-Ubuntu SMP Fri Jul 10 00:24:02 UTC 2020 
x86_64 x86_64 x86_64 GNU/Linux

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