When trying to extract a .rar file with 7zip I encountered an error about an unsupported method. The directory contents of the file were listed, however it wouldn’t extract the files. After alittle reserach I discovered you required the following apparently unreleated plugin: p7zip-rar

sudo apt-get install p7z-rar

after installation, re-run your 7zip command and it will work fine

7z x filename.rar

This applies to 7-zip on Ubuntu and Debian distributions. It may also work for other distributions, however it has not been tested.

Install the full version of 7zip with the rar extensions

To install the full version of 7zip, including the p7zip-rar package to solve the unsupported method error when extracting .rar files use the following command:
sudo apt-get install p7zip-full p7zip-rar