Comment 10 for bug 1902955

Verified 2.31-0ubuntu9.2 in Bionic->Focal upgrade:

The upgrade fails later, due to the broken perl:

Preparing to unpack .../locales_2.31-0ubuntu9.2_all.deb ...
Unpacking locales (2.31-0ubuntu9.2) over (2.27-3ubuntu1.4) ...
Preparing to unpack .../libc6_2.31-0ubuntu9.2_amd64.deb ...
Checking for services that may need to be restarted...
Checking init scripts...
Checking for services that may need to be restarted...
Checking init scripts...

Name Service Switch update in the C Library: post-installation question.

Running services and programs that are using NSS need to be restarted,
otherwise they might not be able to do lookup or authentication any more
(for services such as ssh, this can affect your ability to login).
Note: restarting sshd/telnetd should not affect any existing connections.

The services detected are:
        rsync cron atd

If other services have begun to fail mysteriously after this upgrade, it is
probably necessary to restart them too. We recommend that you reboot your
machine after the upgrade to avoid NSS-related troubles.

Do you wish to restart services? [Y/n]
Stopping some services possibly affected by the upgrade (will be restarted later):
  cron: stopping...done.

Unpacking libc6:amd64 (2.31-0ubuntu9.2) over (2.27-3ubuntu1.4) ...
Selecting previously unselected package libcrypt1:amd64.
Preparing to unpack .../libcrypt1_1%3a4.4.10-10ubuntu4_amd64.deb ...
Unpacking libcrypt1:amd64 (1:4.4.10-10ubuntu4) ...
Setting up libcrypt1:amd64 (1:4.4.10-10ubuntu4) ...
Setting up libc6:amd64 (2.31-0ubuntu9.2) ...
/var/lib/dpkg/info/libc6:amd64.postinst: 17: exec: /usr/share/debconf/frontend: not found
dpkg: error processing package libc6:amd64 (--configure):
...

With perl not being broken do-release-upgrade succeeds as usually.