Using unattended-upgrades on Ubuntu 16.04 (and previous versions) set up to install updates on shutdown, flashplugin-installer always failed when downloading the new version. The reason probably is that on shutdown, the Internet connection is not available anymore. Up to now, I always updated flashplugin-installer manually. But today, I found a nice and simple solution:
Just get rid of the installer! In the Cononical partner repository, there is a package that directly contains the flash plugin. First, make sure you include the partner repository in your /etc/apt/sources.list, e.g. for xenial:
deb http://archive.canonical.com/ubuntu xenial partner deb-src http://archive.canonical.com/ubuntu xenial partner
Then, update, get rid of the flashplugin-installer, and install the adobe-flashplugin instead:
sudo apt-get update sudo apt-get remove flashplugin-installer sudo apt-get install adobe-flashplugin
Hope this helps someone who also has problems with unattended upgrades and falshplugin-installer.