Install unity-scope-manpages by entering the following commands in the terminal:
sudo apt update sudo apt install unity-scope-manpages
Description:
Manual pages scope for Unity
This package contains the "manpages" scope which allows Unity to search technical documents.
Homepage: https://launchpad.net/unity-scope-manpages
Version: 3.0+14.04.20140324-0ubuntu3
Section: universe/gnome