I attempted to download, and install the official 64-bit .deb package for Unity3d on a system with Ubuntu 15.04. Unfortunately, when I attempted to open the deb package in the Ubuntu Software Center, I received this error: “Cannot Install ‘lib32stdc++6’”
Any suggestions? I had successfully installed the Unity3d deb package on an Ubuntu 14.04 system, but now with 15.04 it doesn’t seem to be working.
Did you try using a terminal? Just open up a terminal by pressing Ctrl+T, cd to your Downloads folder (assuming the deb is in there) and use this line: sudo dpkg -i #FILENAME OF DEB#. This will manually install your deb package.
The installer will probably fail due to some missing libraries. In this case, all those c++ libraries you need. If that happens, use this line: sudo apt-get install -f which will install all missing libraries and automatically presumes the installation of unity.