when a damaged rar file doesn't open

Sometimes a damaged rar file won't open using nautilus native extractor.
First you can test the file by

unrar t filepart1.rar

When the files prove right you can

unrar e file.part1.rar

The recovery mode seems only to work using unrar.

Btw under Debian Linux, you need to type apt-get as follows to install unrar program:
# sudo apt-get install unrar