$ sudo apt-get update
$ sudo apt-get install rdiff-backup-fs 

rdiff-backup-fs is installed in your system.

Make ensure the rdiff-backup-fs package were installed using the commands given below,

$ sudo dpkg-query -l | grep rdiff-backup-fs *

You will get with rdiff-backup-fs package name, version, architecture and description in a table

rdiff-backup-fs package basic information: