Hi,

Linux Mint Debian Edition (LMDE) does not include libunrar.so, this means you cannot open RAR files with Double Commander.
If you have seen the annoying "Cannot open existing file" when trying to open RAR files, but other unpackers work correctly, here's how to fix UNRAR.You need to build libunrar.so yourself. Do not despair, it's easy once you know how.
This fix should work in other dists as well.

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Thanks!