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
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 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: (Can't locate Gtk2.pm in @INC (you may need to install the Gtk2 module) (@INC contains: /etc/perl /usr/local/
debconf: falling back to frontend: Dialog