Un-Ubuntuing Ubuntu Redux
Ubuntu ships with the “main” and “universe” repos enabled, and the “multiverse” repo disabled. This is because there are legal or ideological reasons to not use the software in multiverse.
However, there are practical reasons to use the rar/unrar packages from multiverse over the unrar-free package in universe: unrar-free frequently doesn’t work, but unrar-nonfree does.
If you want your compression and decompression software to operate, rather than be ideologically compliant:
sudo apt-add-repository multiverse sudo apt-get update sudo apt-get install unrar rar