- install  build-essential package

apt install build-essential

- download UNRAR source file

http://www.linuxfromscratch.org/blfs/view/svn/general/unrar.html

- extract source file into a new folder

- navigate to the new folder abd run the following command to create the libunrar.so file

# make -f makefile lib

- run the following command to install the libunrar.so file in /usr/lib/

# make install-lib
install libunrar.so /usr/lib
install libunrar.a /usr/lib

- open Double Commander and try to open RAR file

Vlastimil Pošmura, 2018