I ran into this bug, where Cantor can't find the sage backend if both are installed through the ubuntu package system. I can get around this bug if I know the path to the sage executable, but even after installing cantor-backend-sage I can't figure out where sage is located.
find both return loads of files called
message-something, and have been unhelpful.
which sage and
whereis sage return nothing.
Is there some way to figure out where apt-get installs everything in a package?