Refer to https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=945437 for the removals.

$ sudo apt install gdebi-core

To add FSlint to Ubuntu 20.04 and Linux Mint Cinnamon 20:

Download or move into the Home > Downloads folder these three files:

$ wget http://old-releases.ubuntu.com/ubuntu/pool/universe/p/pygtk/python-gtk2_2.24.0-6_amd64.deb  
$ wget http://old-releases.ubuntu.com/ubuntu/pool/universe/p/pygtk/python-glade2_2.24.0-6_amd64.deb
$ wget http://old-releases.ubuntu.com/ubuntu/pool/universe/f/fslint/fslint_2.46-1_all.deb 

In the Terminal App run:

$ sudo apt-get update
$ sudo apt-get upgrade
$ cd Downloads 
$ sudo gdebi python-gtk2_2.24.0-6_amd64.deb
$ sudo gdebi python-glade2_2.24.0-6_amd64.deb
$ sudo gdebi fslint_2.46-1_all.deb
$ sudo reboot

Note: If preferred (thanks go to N0rbert for their post), sudo apt-get install ./*.deb installs all deb’s in a folder in one step, but for simplicity sake, albeit ironic as that may be, I am using gdebi on each deb one at a time. Heck, the antiquated MS Windows user in me may even reboot between installs for peace of mind.

And now FSlint can be used on Unbuntu 20.04 to find and remove duplicate files as well as across an entire QNAP NAS by tunneling to Files > Computer > nas_share in Ubuntu Linux Station 20.04 or also on a PC using Linux Mint 20.

Hopefully, FSlint is updated in 2021. The combo of Ubuntu Linux Station Ubuntu 20.04 and FSlint is a real time-saver on a QNAP, and while I’ve been using Windows and macOS for decades, my go-to operating system to get real GUI-based work done is Linux Mint. The free Open Source app pool available today is simply amazing.

Cheers :)
Jeffrey A. Nowak, Ph.D.

Thank you for this tool.