I am currently running Debian Jessie with the Xfce DE.
I recently decided to replace the Xfce window manager with i3. Running
sudo apt-get remove xfcwm unfortunately caused a lot of very necessary software to be listed as "no longer required" because they were installed automatically with xfcwm; reinstalling xfcwm did not fix the issue.
I would like to know how I can list these packages as "required", or at least as not automatically installed. I tried using
sudo apt-mark unmarkauto, but this only seems to work one package at a time, and there are simply too many packages for this to be a convenient solution.