E: Package 'gksu' has no installation candidate
I have the same installation problems with Linux Mint 19.3 Tricia base: Ubuntu 18.04 bionic.
As mentioned in the previous post, gksu has been removed from Debian, Ubuntu 18.04 and other newer Linux distribution versions. From all accounts gvfs admin should achieve similar functionality by adding admin:// prefix to the path when using terminal. So far no success as the installer still requires gksu.
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