I think you have some movement of the flooring/support under the linoleum which is causing the crack. I repaired a crack in my linoleum which was about an 1nch long and was caused by a Corian table top smashing onto it. First thing I did was to use a dental explorer tool to lift the cut edges up so that the white foam underside wasn't showing and then carefully applied a heavy bodied crazy glue to the crack. I then immediately wiped the top surface with a crazy glue remover so the there would be a minimal amount of shiny material from the crazy glue. Worked really well so far.