Quick note if anyone else are installing Unity from Linux: You won’t find a Linux installer on the big installer page. Instead, install with an AppImage for Unity Hub. With Unity Hub, you authenticate and install the version you want.
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Sign up for a Unity ID
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Download the latest Unity Hub AppImage from the forum. Latest as of 2019-05-10 is Unity Hub 1.6.2
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Make the AppImage executable
chmod +x UnityHubSetup.AppImage - 
Then run it.
./UnityHubSetup.AppImage