update-manager: missing dependency on libgtk2-perl for debconf frontend

The output in your dpkg upgrade log shows:

Processing triggers for shim-signed (1.17~14.04.1+0.8-0ubuntu2) ...
Use of uninitialized value $ret in string eq at /usr/share/perl5/Debconf/FrontEnd/Passthrough.pm line 212, <GEN0> line 22.
Use of uninitialized value $_[1] in join or string at /usr/share/perl5/Debconf/DbDriver/Stack.pm line 111, <GEN0> line 22.
Use of uninitialized value $_[1] in join or string at /usr/share/perl5/Debconf/DbDriver/Stack.pm line 111, <GEN0> line 22.
Use of uninitialized value $ret in string eq at /usr/share/perl5/Debconf/FrontEnd/Passthrough.pm line 212, <GEN0> line 29.
Use of uninitialized value $_[1] in join or string at /usr/share/perl5/Debconf/DbDriver/Stack.pm line 111, <GEN0> line 29.
[...]

This indicates a problem with the debconf prompting code. What program were you running to do the upgrade?

I think update-manager? One of the standard GUI updater things.

Here's a chunk of ps -AF --forest that might help:
alex 6365 1 0 84088 18916 2 Jul30 ? 00:00:00 /usr/bin/python /usr/lib/update-notifier/backend_helper.py show_updates
alex 6370 6365 0 173663 123028 2 Jul30 ? 00:00:11 \_ /usr/bin/python3 /usr/bin/update-manager --no-update
alex 7919 6370 0 17241 14224 2 Jul30 ? 00:00:00 \_ /usr/bin/perl -w /usr/bin/debconf-communicate
root 7180 1 0 76314 66688 2 Jul30 ? 00:00:04 /usr/bin/python3 /usr/sbin/aptd
root 7189 7180 0 76315 47888 3 Jul30 pts/3 01:13:37 \_ /usr/bin/python3 /usr/sbin/aptd
root 7916 7189 0 5261 10480 2 Jul30 pts/6 00:00:00 \_ /usr/bin/dpkg --status-fd 99 --configure shim-signed:amd64 dkms:all x11proto-randr-dev:all
root 7917 7916 0 17788 14340 0 Jul30 pts/6 00:00:00 \_ /usr/bin/perl -w /usr/share/debconf/frontend /var/lib/dpkg/info/shim-signed.postinst configure 1.17~14.04.1+0.8-0ubuntu2
--
[...]
alex 23733 1 0 84089 20524 3 20:54 ? 00:00:00 /usr/bin/python /usr/lib/update-notifier/backend_helper.py show_updates
alex 23738 23733 2 166574 182760 0 20:54 ? 00:00:02 \_ /usr/bin/python3 /usr/bin/update-manager --no-update

This is related to bug #1679435 and bug #1679784. Since those bugs are fixed, this bug is effectively masked right now, but this package should still have proper depends/recommends so that it doesn't accidentally crop up again later.

One way to get an error message out of update-manager about this is to remove libgtk2-perl, if it is already installed, and run update-manager via a terminal. When a package like software-properties-gtk is installed you'll see the following message in the terminal:

debconf: unable to initialize frontend: Gnome
debconf: (Can't locate Gtk2.pm in @INC (you may need to install the Gtk2 module) (@INC contains: /etc/perl /usr/local/lib/x86_64-linux-gnu/perl/5.24.1 /usr/local/share/perl/5.24.1 /usr/lib/x86_64-linux-gnu/perl5/5.24 /usr/share/perl5 /usr/lib/x86_64-linux-gnu/perl/5.24 /usr/share/perl/5.24 /usr/local/lib/site_perl /usr/lib/x86_64-linux-gnu/perl-base) at /usr/share/perl5/Debconf/FrontEnd/Gnome.pm line 91.)
debconf: falling back to frontend: Dialog

This bug was fixed in the package update-manager - 1:17.10.2

---------------
update-manager (1:17.10.2) artful; urgency=medium

  * Recommend libgtk2-perl be installed so we have a working debconf frontend.
    (LP: #1607929)

 -- Brian Murray <email address hidden> Tue, 18 Jul 2017 15:32:54 -0700

Hello Alex, or anyone else affected,

Accepted update-manager into xenial-proposed. The package will build now and be available at https://launchpad.net/ubuntu/+source/update-manager/1:16.04.8 in a few hours, and then in the -proposed repository.

Please help us by testing this new package. See https://wiki.ubuntu.com/Testing/EnableProposed for documentation how to enable and use -proposed. Your feedback will aid us getting this update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug, mentioning the version of the package you tested, and change the tag from verification-needed to verification-done. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed. In either case, details of your testing will help us make a better decision.

Further information regarding the verification process can be found at https://wiki.ubuntu.com/QATeam/PerformingSRUVerification . Thank you in advance!

Hello Alex, or anyone else affected,

Accepted update-manager into trusty-proposed. The package will build now and be available at https://launchpad.net/ubuntu/+source/update-manager/1:0.196.24 in a few hours, and then in the -proposed repository.

Please help us by testing this new package. See https://wiki.ubuntu.com/Testing/EnableProposed for documentation how to enable and use -proposed. Your feedback will aid us getting this update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug, mentioning the version of the package you tested, and change the tag from verification-needed to verification-done. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed. In either case, details of your testing will help us make a better decision.

Further information regarding the verification process can be found at https://wiki.ubuntu.com/QATeam/PerformingSRUVerification . Thank you in advance!

Hello Alex, or anyone else affected,

Accepted update-manager into zesty-proposed. The package will build now and be available at https://launchpad.net/ubuntu/+source/update-manager/1:17.04.5 in a few hours, and then in the -proposed repository.

Please help us by testing this new package. See https://wiki.ubuntu.com/Testing/EnableProposed for documentation how to enable and use -proposed. Your feedback will aid us getting this update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug, mentioning the version of the package you tested, and change the tag from verification-needed to verification-done. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed. In either case, details of your testing will help us make a better decision.

Further information regarding the verification process can be found at https://wiki.ubuntu.com/QATeam/PerformingSRUVerification . Thank you in advance!

I removed the package libgtk2-perl from my testing system, then I installed the version of update-manager (17.04.5) from zesty-proposed. While the package was installing I observed libgtk2-perl also being installed. Additionally, when I ran the new version of update-manager I did not see any error messages about being unable to initialize the Gnome frontend.

I removed the package libgtk2-perl from my testing system, then I installed the version of update-manager (16.04.8) from xenial-proposed. While the package was installing I observed libgtk2-perl also being installed. Additionally, when I ran the new version of update-manager I did not see any error messages about being unable to initialize the Gnome frontend.

I removed the package libgtk2-perl from my testing system, then I installed the version of update-manager (1:0.196.24) from trusty-proposed. While the package was installing I observed libgtk2-perl also being installed. Additionally, when I ran the new version of update-manager I did not see any error messages about being unable to initialize the Gnome frontend.

This bug was fixed in the package update-manager - 1:0.196.24

---------------
update-manager (1:0.196.24) trusty-proposed; urgency=medium

  * Recommend libgtk2-perl be installed so we have a working debconf frontend.
    (LP: #1607929)

 -- Brian Murray <email address hidden> Mon, 24 Jul 2017 17:43:27 -0700

The verification of the Stable Release Update for update-manager has completed successfully and the package has now been released to -updates. Subsequently, the Ubuntu Stable Release Updates Team is being unsubscribed and will not receive messages about this bug report. In the event that you encounter a regression using the package from -updates please report a new bug using ubuntu-bug and tag the bug report regression-update so we can easily find any regressions.

This bug was fixed in the package update-manager - 1:16.04.8

---------------
update-manager (1:16.04.8) xenial; urgency=medium

  * Recommend libgtk2-perl be installed so we have a working debconf frontend.
    (LP: #1607929)

 -- Brian Murray <email address hidden> Mon, 24 Jul 2017 17:40:35 -0700

This bug was fixed in the package update-manager - 1:17.04.5

---------------
update-manager (1:17.04.5) zesty; urgency=medium

  * Recommend libgtk2-perl be installed so we have a working debconf frontend.
    (LP: #1607929)

 -- Brian Murray <email address hidden> Mon, 24 Jul 2017 16:43:12 -0700